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Forward and inverse modelling of potential field data

1. XX C XY C YY C ZX C YZ C ZZ C Trace ie zero invariant C N ie first invariant C DETERMINANT ie 12 MAX eigenvalue MID eigenvalue MIN eigenvalue Ratio ie 12 11 Strike ie atan I2 l1 Octahedral Normal Octahedral Shear Cube Root Determinant Square Root First Invariant Scaled Moment Phase Modulo OK 2 te fe fe fe fe fe fe fe fe fe fe Cancel z P Intrepid Visualisation o 6 File Line Display Point Display Grid Display Polygon Display Window Help ay E AEDH calculated_Gravil LINE PNT POLY Ten XX lt x Line FID1 FID2 Dist m Z Value Km Zoom In 2 daak Zoom Previous Mouse Mode Query C Zoom or Trace OOBE B BBE z 7 Now select YZ gt OK The tensor derivative grid of the gravity gradient in the composite directions z and y is displayed Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Tensor Query Options for Tensor Grid Dataset C XX C XY C YY DX NZ EC 22 C Trace ie zero invariant C 11 ie first invariant C DETERMINANT ie 2 C MAX eigenvalue Tutorial case study E Forward and inverse modelling of potential field data 95 lt 4 Back gt Fl Intrepid Visualisation File Line Display Point Display Grid Display Polygon Display Window Help B boe calculated_Gravil LINE PNT POLY Ten YZ x Y Line F
2. Parameters _ ____________ __ _ Parameters Law simulation wal 2 9 0 2 30 Mode 1 Mode 2 y OK X Cancel Tutorial case study E Forward and inverse modelling of potential field data 29 lt 4 Back gt 2 Set each component in turn Use the slide bar for the first component to set 70 of the population The other 30 will automatically assign to the 2nd population 3 Choose OK 3D GeoModeller updates property definitions in the table with the revised mean standard deviation and percentage values Finalise density and magnetic susceptibility properties Steps Even though the first exercise forward modelling is for gravity only we will also finalise the magnetic susceptibilities for all 3 geological formations in our model ready for our later joint inversion exercise Densities eee e toa tego o Sereno 29 o2 nomar arcomon Magnetic Susceptibilities we will not be setting Remanent Magnetization Series2 Host_rock 0 002 0 0001 LogNormal 1 Ensure all of the values in the above tables are entered and then Save 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Formation Density g cm E Cover Normal 2 2 0 1 100 HB Host rock Log normal 3 1 0 1 70 Normal 2 9 0 2 30 Normal 2 8 0 1 100 General Parameters Densit
3. Ep Project Zone P Help wi OK Xx Close 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 20 Contents Help Top Contents Help Top q Back gt View the modelled geology To see the modelled geology we need to interrogate the model equations We can 3 Plot the modelled geology on any section in the model Create a new section and plot the modelled geology on it Build the 3D shapes of the modelled geology and view in the 3D Viewer Select C3 section in the 2D Viewer click the window amp a tick appears in the top left corner From the Model toolbar choose Plot the model settings or press ctrl D In the Plot the model settings dialog box Check all 3 Show Fill and Show Lines Choose OK rJ Plot the Model Settings Number of Nodes u Direction 50 v Direction 50 Node Spacing u 252 1 v 40m More L J Select All Deselect All Invert Select All Deselect All Invert Select A eselect A alata ne ee eee x The fill and lines of the modelled geology are plotted on the vertical 2D Section C3 4 5 Repeat these steps and plot the modelled geology on some of the other sections Save your project From the main menu choose Project gt Save or from the toolbar choose Save or press ctrl
4. Percentage of Population 0 50 100 Description Unit ST Law simulation Log normal 2e 005 1 006 100 30 25 i ii 204 ap 154 104 fs Ji a5 5 g0 0 00000 0 00001 200007 Susceptibility 1 Mode 1 Help a OK Cancel 2 OK toclose and save the new Mn and SD values Staying in the Magnetics tab note the 3 fields below the IGRF Calculator where you can enter ambient field properties Total magnetic field Declination and Inclination Ideally use the IGRF calculator to automatically fill these 3 fields based on the model location known from the Projection System Project amp height datum of the project See Project gt Properties But as this project uses a Local system we must enter them manually 3 The BuriedGranite model is fictitious but nominally located in northern South Autralia in WGS 84 zone 54S Our geophysics surveys were acquired on 1st Jan 2010 Therefore please enter Total magnetic field nT Declination degrees Inclination degrees Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 27 Contents Help Top 4 4 Back gt EZ Physical Properties Gravity Magnetic Thermal Advection seismic Formation Susceptibility SI Remanent Magnetization A4 m Cove
5. Back gt quantity normally measured in an aeromagnetic survey Gravity Tensors and the following 6 separate components Gxx etc and Magnetic Tensors and the following 9 separate components Mx etc are the gravity and magnetic field gradients in the x y and z directions correspond to east north and up See Tutorial E6 for further details and a demonstration exercise Below is an image of the observed gravity 10km x 10km 7 6 to 18 8 mGal Linear colour stretch Contour spacing 1 mGal gt gt gt File Line Display Point Display Grid Display Polygon Display Window Help m Intrepid Visualisation Observed Gravin LINE PANT POLY signal koi Y Line FID 1 FID 2 Dist m Z Walue Em 400CH foom Previous Fdouse Mode C Query C Zoom or Trace The aim of our forward modelling exercise is to achieve a close fit of the gravity response from our current geology model compared with the observed response above The observed response is the unknown geology which is our target and that which we seek to discover during the course of this tutorial Our investigation is typical of an exploration approach adopting geophysical inversion Our starting geology model begins as a best guess at the true sub surface geology which in nature is never known with complete certainty As more geological data can be added to the model through drilling sampling and mapping and or potential field geop
6. Contents Help Top lt 4 Back gt compare your model response calculations to what might be given to you from an airborne geophysics contractor grid Choose NEXT Select 3D FFT method Set the vertical expansion to 1200 O CO NOA Accept the default values for x y and z of the Voxet Properties Accept all the remaining defaults in the remaining part of this window r 3 Create Forward Case Voxet Properties Set voxet resolution and processing options Voxet extents and resolution Xmin 0 Xmax 10000 dX 500 nX Ymin 0 Ymax 10000 dY 500 nY Zmin 2000 Zmax 0 dz 100 nz Processing Options 5 Spatial e satio 3D FFT Expansion Method Mirror UseLanczos Taper Save Response Voxet Expand vertically by 1 200 Save Expanded Voxet Memory requirements 12 MB amp Accuracy Estimate lt Bak Next gt 20 20 Reset extents 10 Choose NEXT series NEWgranite may also appear in this list 3 Create Forward Case Lithology Physical Properties Type Formations property Value ensi Log normal 0 1 100 General Indude Border Effect Reference density Above topo density Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 92 Contents Help Top 4 Back
7. Modification rejected Modification accepted lie Continue Finish At the beginning of an iteration 3D GeoModeller makes a small change to a boundary between different formations to physical properties or to both It assesses the suitability of the change against criteria such as whether this has preserved the network of interconnections between formations the topology of the model If the change fails the test 3D GeoModeller rejects it and concludes the iteration If it passes the forward potential field response of the modified model is calculated 3D GeoModeller applies a second set of tests favouring acceptance of models that reduce the misfit between the predicted and observed response It does not however completely exclude the possibility of accepting a change that increased this misfit This important aspect of the algorithm enables us to explore many different model configurations If the modified model passes all tests the changes are accepted The modified model becomes the input for the next iteration This loop continues until 3D GeoModeller has reached the maximum number of iterations specified or you stop the program This is not a deterministic solver the misfit does not determine when the solver will stop but rather when the solver has converged to a starting point where all subsequent models will fit the data with the same likelihood and from which point statistical records and movies can sta
8. tops of the MostProbable Geology as a point cloud and then re import them as primary geology constraints new granite 1 From the Main menu open Geology gt Formations Create or Edit 2 Select a colour and type a name say NewGRANITE No spaces gt Add Geology Formations Mi Cover _ p E Host_rock I Create Geology Formation Name Pad Pe Bow Elo E 3 Select Yes Start Stratigraphic Pile editor New formationis have been created They have not yet been added to the Stratigraphic Pile Do you wish to do this now Don t show this again pune No Do it later Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 80 Contents Help Top 4 Back gt 4 Select gt New Series Create or Edit Geology Series and the Stratigraphic F Reference SS Bottom TE Format Relatio E New Series Cover Onlap lt Series_2 Host_r k Onlap BR Eat a Move up V Move down TEJ Export Fd close 5 Highlight gt NEWgranite gt Commit gt Close gt Close TB creare Geology Serie i it Se Properties Name of the Series NEWgranite_Series Relationship Onlap w Contents Available Formations Dykes Formations Dykes in Series a Remo
9. _ 5750 0 E 4760 0 gt 3750 0 2750 0 1750 0 750 0 250 0 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m Misfit Regional Trend 2 368742 lt v lt 1 992231 Observed_Gravimetry_BuriedGranite 4 8750 0 8750 0 8750 0 7750 0 7750 0 7750 0 6750 0 6750 0 6750 0 _ 5750 0 5750 0 5750 0 E 4760 0 E 4760 0 E 4760 0 gt 3750 0 gt 3750 0 gt 3750 0 2750 0 2750 0 2750 0 1750 0 1750 0 1750 0 750 0 750 0 750 0 250 0 250 0 250 0 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m X m X m Cs 01 02 03 04 10 1 1 15 1 20 15 10 O5 00 05 10 15 Regional Settings Degree 0 Constant w Regional 0 367898 Apply 3D GeoModeller displays several images and some basic statistics when the forward model calculations have been completed The images are Top Left the observed grid Top Centre the response of the current model that you have calculated Top Right the current misfit or difference in response between the response of the current model and the observed grid e Bottom Left is the result of choosing a DC shift and asking the tool to solve for a best fit degree The surface is horizontal so no grid is apparent here The solved degree is displayed on bottom bar in Regional field e Bottom Middle is the computed response with the DC sh
10. 15 Step 1 of 4 Select Tops NEWgranite cvs gt Open gt Next g CSV Data Import 3D Interfaces Oa St i Select data type to import Step 1 of 4 1 Select data type to import File to Load 2 Parse CSV file PEN E in a h D TEMP_PDAC_Tutorial_E TutorialE5 E5Completed Project Tops_NEWgranite csv Lookin E5Completed_Project eH di Casel J MeshGrids ra Tops_NEWgranite csv File name Tops_NEWgranite csv Network Files of type Al Acceptable Files 16 Step 2 of 4 Observe 3 separate columns are recognised for x y and z gt Next F V Text qualifiers Decimal separator E Ls Semicolon F C Comma E 7 Double Quote E Dot Map cams objects in Other E C Single Quote E L Comma File reading parameters Data start at row Preview entire file 50 E Fixed columns Treat consecutive delimiters as one Skip leading spaces E E 2250 000000 _ z750 000000 4500 000000 id 3250 000000 1500 000000 3 3750 000000 1500 000000 2250 0 00000 4250 000000 1500 000000 2250 0 00000 4750000000 1500 000000 2750 000000 4250 000000 1400 000000 2750 000000 4750 000000 1400 000000 Column Size Auto Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Tutorial case study E Forward and inverse modelling of potential fiel
11. Appearance gt Display mode Wireframe gt Apply gt Close Compute a New Field for viewing granite by post burn in density distribution 1 In Explore select Meshes and Grids gt Hide all Views 2 With SummaryStats_400000_500000_Threshold_90_super vo selected right click gt Compute new Field All fields to be computed must be within the same grid Functions such as Merge Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd lt 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 78 Contents Help Top 4 Back gt this grid with Another can assist manipulation Calculator Expression to evaluate Eg if Density nan 2 7 Density nb seperator is Jif MostProbable 1 MeanDensity nan Field Name GraniteBYDensitycontrast List signal Functions Keyboard excensty tt mnths ut ml ta StaDevDensi F j enn iia a aaa a a Ge E E i a sh cosh im tanh am asinh aos atanh a a 3 Inthe Grid Computer type select If MostProbable 1 THEN MeanDensity OTHERWISE null and close the bracket 4 From EXPLORE select 3D Geology gt Hide 5 Give the new field a name top right of Calculator say GraniteBY Densitycontrast 6 Evaluate then Save and exit 7 From EXPLORE select Summarystats_400000_500000_Threshold_90_super vo gt Hide all Views of this mesh egrid 8
12. Density field of the same initial voxet Repeat Steps 5 6 and 7 Note the spikes in the histogram occur because only mean values of density per lithology were used in forward modelling gravity 3D View a mig X Histogram of Density xa g O bg Statistics Histogram of Density P Val 5 000 roperty alue 00 arso Mota eooo n Effective 8000 55 4 ia in Nulls t 4 250 Nulls 0 50 4 000 Min 0 47 i Max 0 37 3 45 370 Mean 0 115585 pasoo Std Deviation 0 363822 40 3250 Kurtosis 1 041232 L300 gt iSkewness 0 915462 Mean 0 115585 Sigma 0 36 3 000 po E 35 naati Variance 0 132366 a re t2750 9 aes D a t2500 gt Q a0 D 2 250 3 sal 2 000 s 1 750 20 t 1 500 15 t 1 250 t 1 000 750 t 500 5 250 o lt gt d4 g 05 0 4 03 0 2 0 1 0 0 0 1 0 2 03 0 4 a Density Set Clipping Parameters of the 3D voxet To slice and interrogate a voxet you can clip the 3D view in the directions x y and z 1 First ensure only one voxet Density is in the 3D viewer by right clicking Initial gt Lithology gt Hide Field from all views 2 Select the Set Clipping Parameters 3D tool on the bottom of the right hand side 30 View n BDE aS E E 3 a o m s Set Clipping Parameters Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Bac
13. Forward and inverse modelling of potential field data 84 Contents Help Top q Back gt e They are currently committed to a new geology object NEWGranite and included in the geological pile g 3D view m i Ed Re comuting the 3D granite iso surface in the model with post inversion constraints e In this step we modify the initial geology model replacing of the old granite contact points with the NEWeranite contact points The first step 1s to add some orientation data for NEWeranite as a rule both orientation amp points data are required to compute a surface 1 From Main menu select Model gt Project Data onto Sections in 2D Viewer Select Section C2 Select NEWegranite Type Maximum Projection distance 500 gt OK With Section C2 active tick in the top left select the Create tool from the 2D toolbar pencil tool 6 Guidance for the shape of the NEWeranite is needed on Section C2 oF N Use the Create tool to click in 2 places and select gt Create Geology Orientation data from the top toolbar Menu 7 For each of the 3 orientations check NEWegranite is selected gt Create bottom Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 85 Contents Help Top 4 Back gt wf amp C2 LOIT Seation 4iui ae Create Geol
14. From EXPLORE select the new field GravityBYDensitycontrast 9 Right click gt Field Visualisation Manager 10 Select View grid in 3D gt OK 33 SummaryStats_125000_200000_Threshold_90_super 14 ChangeCount i Entropy EE MeanDensity EE stdDevDensity EE MeanSusceptibility StdDevSusceptibility MostProbable EE MostProbableThresholded Prob_AboveTopo Prob_Cover EN Prob_Granite ap Iso values 3D Grid 3D View Sections View Sections View on Section View on Section in 3D All W MNT Ci C2 m f ws Parameters Display Color Table Contouring Edit Colours and Clips Lv vo sey Eco 11 The View below opens in 3D Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 79 Contents Help Top 4 Back gt iia Color Table ee ee bag ee oe A P o Si ont wjt a i 5 a n Di Ae ggo Doon HATH 6000 0 05 GraniteBYDensity ae YF anno 0 00 pao 771500 doo 1 Aditionally you can open the colour table from EXPLORE gt Grids and Meshes gt GranitB YDensitycontrast gt Display Colour Table E5 Stage 9 Create 3D points of inversion driven geology Export Shells cvs A key method for re importing the post inversion geology geometry is demonstrated in this section First we export the
15. Point Dataset LINE Load Poly Dataset PNT Load Grid Dataset aan Load Ternary Grid Dataset x Y Map Line Save 3 Band Image aie i Load Options meee Save Options Km Quit Zoom In Zoom Previous Mouse Mode C Query C Zoom or Trace 3 Browse to D CaseStudyE TutorialE6 E6Beginning Project Case3 Run1 calculated_ GravityTensors_l ers 4 The computed full tensor gravity grid is visualised same as the top middle Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 94 4 Back gt grid of the previous Results Explorer summary figure above This visualisation is available to us through a Cube Root Determinant function FI Intrepid Visualisation BAHAN gg bo la faa File Line Display Point Display Grid Display Polygon Display Window Help calculated_Gravii LINE PNT POLY Ten default_quer Y Line FID1 FID2 Dist m Z Value Km Zoom In Zoom Previous Mouse Mode C Query C Zoom or Trace TROBE 5 Within the small Intrepid Visualization window open Grid Display gt Tensor Query bottom of the list 6 Select XX gt OK The tensor derivative grid of the gravity potential purely in the x direction is displayed 5 Tensor Query Options for Tensor Grid Dataset
16. S Explore model plotting options Experiment with other options in the Plot the model settings dialog box Check Show Trend Lines Choose Apply to All to render the 3D model on all open 2D sections For Show Trend Lines or Show Fill select or de select various combinations of formations Choose Show Trend Lines in combination with Show Lines amp or Show Fill Modify the Plotting resolution from the default u 50 v 50 to say 100 x 100 Experiment with the three plot buttons in the Model toolbar Model gt Plot the model settings or press ctrl d 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 21 Contents Help Top 4 Back gt e Model gt Plot the model on the current section e Model gt Plot the model on all sections 7 Experiment with the Section display parameters Right click on the background of an active 2D section e Choose for example C3 gt Display parameters This allows you to toggle between different views which are already rendered For example Model geology gt geology lines tick OR geology fill tick i C3 MNT F4 Fr Section 400 Explore the 3D Viewer Build the model in 3D 8 From the Model toolbar choose Build 3D Formations and Faults i Build 3D Formation and Fault Shapes 3D Shape Parameters Type and Mesh Res
17. X DIRECTION a Daa T Y DIRECTION Gzy 2 YH This is the horizontal gradient xz of the vertical component xy of the gravitational acceleration S7 Z DIRECTION 3 Now press NEXT and go to the next page of the wizard Forward Model Parameters Unlike our previous forward modelling tutorial E2 we will not browse for load an observed reference Gravity Tensor grid This will be included in the extension tutorial currently being prepared Choose a calculation surface The choice is open since we are not matching the metadata of a reference grid 4 Choose Constant elevation 0 m This is the default and assumes the data was collected at sea level Co feats Lower Forward Model Parameters Set parameters for field 1 of 1 GravityTensors Observed Grid Specify an Observed Grid From External Resource Band Calculation Surface Drape gt Terrain dearance gt Drape Load from dataset Alternatively you can create a calculation surface which mimics the shape of your DEM but for a set terrain clearance height e The final option allows you to load an external drape grid that you want your model response estimated upon This is the closest option to being able to Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 91
18. about the mapping and inversion modules in 3D GeoModeller Aurore Joly T Campbell McCuaig Leon Bagas 2010 The importance of early crustal architecture for subsequent basin forming magmatic and fluid flow events The Granites Tanami Orogen example Precambrian Research 182 1 2 pg 15 29 Bosch M 1999 Lithologic tomography from plural geophysical data to lithology estimation J Geophys Res 104 749 766 Bosch M Guillen A Ledru P 2001 Lithologic tomography an application to geophysical data from the Cadomian belt of northern Brittany France Tectonophysics 331 197 228 Calcagno P Courrioux G Guillen A Chiles J P 2008 Geological modelling from field data and geological knowledge Part I Modelling method coupling 3D potential field interpolation and geological rules Physics of the earth and planetary interiors 171 147 157 Chiles J P Aug C Guillen A Lees T 2004 Modelling the Geometry of Geological Units and its Uncertainty in 3D From Structural Data The Potential Field Method Proceedings of Orebody Modelling and Strategic Mine Planning Perth WA 22 24 November 2004 AusIMM 313 320 Guillen A Calcagno P Courrioux G Joly A Ledru P 2008 Geological modelling from field data and geological knowledge Part II Modelling validation using gravity and magnetic data inversion Physics of the Earth and Planetary Interiors 171 158 169 Guillen A Courrioux G Cal
19. all results in attributed voxets 8D grids for a post burn in phase of your choice Inversion Completed Do you want to compute the Summary Voxets now Mo Cancel Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 64 Contents Help Top 4 Back gt 1 Choose Yes to immediately compute the Summary Voxets If you decline the first time or wish to calculate SSS for a different burn in point you can return to accepting this request through a misfit screen by opening Geophysics gt 3D Geophysics gt Summary Voxets from Inversion 2 Choose a burn in point of 400 000 and type it in the From box lower left This is where the misfit becomes more or less constant at 1 1 as shown by the graph below Your burn in point may be different if different settings have been applied Note the mouse 1s interactive with the misfit plot to display a label Setting the burn in gives the starting iteration for statistical analysis of that portion of the inversion corresponding to simulations that are all equally plausible usually through to and including the last iteration Burn in is judged by observing where the misfit becomes more or less constant despite best efforts to perturb the model 3 Choose OK to create a summary statistics mesh grid voxet for re compile
20. data 51 Contents Help Top 4 Back gt Tutorial E4d Prior Only Inversion fixed properties geology only inversion The aim of this tutorial is to walk through a simple practical example of how to set up a Prior Only geophysical inversion designed to improve your knowledge about the geology geometry and the rock properties of your project The reference manual contains further references and detailed explanations E4 Introduction Parent topic Our last main objective before running the joint inversion which will explore both Tutorial case properties and geology space is to calibrate the tightness or looseness of geological study E S l boundaries explored during an inversion This is best done while the properties are Forward and inverse fixed delli f See cia Forward modelling E2 demonstrated that a reasonably close fit to the observed data gravity potential field was achieved from our initial 3D geology model Further refinements to the properties was achieved in Tutorial E3 through Property Optimization We are now reasonably confident of the assigned physical properties of the geological units in our 3D model lets say through a combination of Property Optimization and because drilling and sampling has provided direct data for densities and magnetic susceptibility values Therefore we have confidence to soon proceed to a litho constrained inversion but first we need to perform prior only in
21. geology model using measured or assumed physical property values for each geology formation is strongly recommended This way you can compare the predicted with observed gravity and magnetic responses and manually make changes to your 3D GeoModeller model or changes to the assigned physical properties if these are not known with high level certainty Forward geophysical modelling followed by revisions to the geology model geometry and physical properties densities and magnetic susceptibilities may need to be repeated to achieve a close starting model These are considered to be the gross scale necessary modifications to complete carefully before embarking on inversion Strategies for achieving successful inversions of geophysical data Parent topic Introduction to Case Study E Contents Help Top Overall strategy for building robust 3D geology models Sequential evolution This section describes a recommended strategy for achieving successful inversions of geophysical data directly from 3D geology models Whilst not required to complete all of the following cases in sequential order the following list gives ideal cases which if carried out and verified separately gives the user the best possible chance of achieving a desired inversion that will be robust from all points of view good convergence realistic geology outcomes tight statistics etc 1 Forward Model Propose a start model e compute gravity response T
22. gt 11 Density property per lithology can be altered entries here will dominate the settings of those in the Physical Properties table No changes necessary 12 As we are creating a Free Air anomaly the appropriate settings for Reference density and Above topo density are both zero Change the values to 0 in this window 13 Now choose NEXT 14 Finally choose the default of Interactive mode 15 The number of CPU s available for this computation is displayed You can accept the full availability or choose to reduce this value to allow other processes to continue Note this will result in slower computation times 3P Create Forward Case so gt B 3 e a J Runtime Settings Interactive E Batch Use profile local Edit Set as defaults Number of Cores 16 Choose FINISH Summary images of the full tensor response for gravity 3D GeoModeller displays the images of the response of our gravity forward calculation of the full tensor in the Results Explorer window This Forward Viewer can be returned to at a later time Geophysics gt 3D Geophysics gt Results Explorer BS Forward Viewer D TEMP_TUT_E Projects Tutoria Completed_Project inversion xm _ e File Help H B case1 Gravity data W Case2 calculated_GravityTensors_1 5 BB Cases Observed 0 lt v lt 0 Computed 36 274 lt v lt 89 774 Misfit 89 774 lt v lt 36 274 Common paramete
23. section In Explore right click on the grid name then gt Hide all views of this field GA Drilholes E g 3D Geology u Grids and meshes e a calculated_Gravimetry_1 a T calculated_Gravimetry_1 8 Finally to see a colour table for the loaded grid Select Calculated_Gravimetry_1 in the Explorer tree Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top 9 Right cick gt Display Colour Table Color Table O NM ww Fann co oO hark dw hd meer Elo calculated_Gravimetry_1 RAW Tutorial case study E Forward and inverse modelling of potential field data 42 lt 4 Back gt Remember that interpolated geology boundaries lines can be switched on off in this view to aid interpretation Right click in the background of the 2D window display parameters This MTN surface geology section is dominated by the Cover unit hence only the fault iso line is rendered in blue lower right Next we will view a histogram of the forward modelled gravity grid 2D 1 In Explorer choose calculated_Gravimetry_1 below Grids and meshes 2 Right click and choose Histogram The y axis is in mGal Is Histogram of calculated_Gravimetry_1 Histogram of calculated_Gravimetry_1 y1 7 Mean in oO calculated_Gravimet N on Pro 619734 Sigma 5 574406 IL calculated_Gr
24. simplest regional trend 2 linear a more complex regional trend type For this case study select 0 Constant 2 Next select Solve bottom right hand side Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 38 lt 4 Back gt p caset Common parameters Forward Viewer D TEMP_PDAC_Tutorial_E TutorialE2 E2Completed_Project inversion xml File Help bobas cavity data calculated_Gravimetry_1 Observed 7 400869 lt v lt 18 51615 Observed_Gravimetry_BuriedGranite 8750 0 7750 0 6750 0 5750 0 4750 0 3750 0 2750 0 1750 0 750 0 250 0 Y m 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m 0 2 0 0 2 0 10 0 12 15 0 1 Regional Trend 0 367898 lt v lt 0 367898 calculated_Gravimetry_1 Computed 6 142409 lt v lt 18 44286 calculated_Gravimetry_1 8750 0 7750 0 6750 0 _ 5750 0 E 4760 0 gt 3750 0 2750 0 1750 0 750 0 250 0 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m cay ne Ps x a Computed Regional Trend 6 510307 lt v lt 18 074962 calculated _Gravimetry_1 Misfit 2 736639 lt v lt 1 624333 Observed_Gravimetry_BuriedGranite 8750 0 7750 0 6750 0
25. to be close to the true models The algorithm generates a sequence of linked models that are similar to these starting models by 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 6 Contents Help Top lt 4 Back gt making small random changes to the lithological boundaries and physical properties After each change is made the likelihood of this combination of models is assessed by comparing the predicted potential field response to the supplied observations The proposal is then accepted or rejected The algorithm preferentially samples models that have greater likelihood It is however important for you during the monitoring stage of the inversion to decide if this likelihood equates to reproduction of the observations within a reasonable uncertainty envelope If this is not the case then you must make changes to one or more of the following The starting litho model The physical property distributions assigned to each formation e The uncertainty levels associated with the geophysical data You can run another inversion session using the modified inputs At the conclusion of an inversion session 3D GeoModeller carries out an analysis of the ensemble of models that was generated Although this analysis is restricted to models that reproduced the observations to an acceptable degree t
26. to the 3D distribution of physical properties If we can sensibly relate physical properties to the units used in the geological map then the potential field data can provide additional insight into the 3D distribution of the mapped units Potential field data are often readily available and uniformly sampled enhancing the value of these data The purpose of this tutorial is to show functionality available in the 3D GeoModeller geophysics modules so that you can apply this powerful technique to your own project In this section e Definitions and references e Interpretation phases e Overall strategy e The geological scenario and starting 3D litho model Introduction to litho constrained inversion of gravity and magnetics e Physical properties e Prior geological information e The need for a close initial 3D geology model e Strategies for achieving successful inversions of geophysical data Inversion analysis flowchart e Overview of steps for this case study 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 2 Contents Help Top 4 Back gt Definitions and references Parent topic Introduction to Case Study E Parent topic Definitions and references Contents Help Top In geophysics the term forward modelling refers to the process of calculating a response given a physical pro
27. values are shown as we have not set considered values yet Physical Properties Physical Properties Seismic Formation Density g cm armati Susceptibility 51 Remanent Magnetization Cover Normal 67 0 100 Normal 0 0 100 0 0 E Host_rock Normal 2 67 0 100 Normal 0 0 100 0 0 ee eae Normal 2 67 0 100 Normal 0 0 100 0 0 General Parameters General Parameters Density Magnetization Reference Density g cm 2 07 E IGRF Calculator Total Magnetic Field nT 50000 Declination degrees 0 Incination degrees 90 eo Eee va Ea In each of the five tabs of the dialog box the top section contains a table of physical properties for each formation in the geological pile Double click within the appropriate cell to view or modify the parameters In the lower half of each tab of the dialog box you can set parameters that apply to all formations in the model In the Gravity tab use the Reference density to convert absolute density values from the table to relative density for the calculations The reference density is often but not always related to the density used for the Bouguer or terrain corrections applied to gravity data The standard density used for this purpose is 2 67 g cm No changes to be made here yet In the Magn
28. voxel adopted for the majority of the iterations between burn in and the last iterations Most Probable Thresholded As above but rather than majority the voxel location must have adopted a single lithology identity for equal to or greater than the threshold number of iterations between burn in and the end of iterations Otherwise a zero is recorded instead of a lithology integer A higher value requested will return a greater level of geological certainty per formation but less of the model will be designated to any formation and zeros of uncertainty will fall between creating a wide geological boundary Probability Cover For every part of the model space the probability of finding Cover in any given cell is given between 0 and 100 This is usually then displayed in a black grey white colour scale Probability_Granite For every part of the model space the probability of finding Granite in any given cell is given between 0 and 100 This is usually then displayed in a black grey white colour scale Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 74 Contents Help Top 4 Back gt File s Description Probability_Host_rock For every part of the model space the probability of finding Host_rock in any given cell is give
29. 0 c l Adjust Color Curve MostProbableThresholded SummaryStats_400000_5001 o Data Clip Data Limits Visibility Clip Custom Colour J Model Pile Transformation Mode Pile 12 Apply amp Close 13 Next ensure that section C2 is open in the 2D Viewer G B Faults L E Sections i oF eee E Ps Open 2D Viewer kia Grids Shading al Dy Appearance 3 i ie Reset View a ae i Export Ed 2 ee p Copy E f Delete a Delete Data d a ke Properties 14 Again with MostProbableThresholded selected right click gt Field Visualisation Manager 15 Select View on Section C2 3D Grid 30 View 30 Points E view Isosurfaces in 3D sections View View on Section View on Section in 30 E E Oo K Farameters Display Color Table Edit Colours and Clips Lo 16 The image below is a 2D rendering of the 3D voxet for MostProbableThresholded Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 76 Contents Help Top 4 Back gt geology at 90 confidence limits an inversion outcome for the granite This is directly compared in the 2D Viewer with the data which constrained the shape of the granite in the initial starting model In accordance with the volume results a WYO SG Visualising the 3D Voxet for Mos
30. 013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 66 4 Back gt E5 Stage 6 View the final 2D grids for magnetics and gravity quality check The reason for this stage comparing observed with final geophysics grids is to evaluate that inversion drove geometry and rock properties changes to achieve a close fit as expected Ifthe geology tests had been too tight e if the initial geology model was not a good close enough fit e if the understanding of rock properties was poor and was not improved by property optimisation THEN poor matches between observed and final computed grid will probably occur On the other hand good agreement between observed and final computed grids does not guarantee that the inversion regime was appropriate or has necessarily given us good results Before concluding this we must also discover and analyse the changes that were driven in terms of the property arrays and geology geometry Load the summary final geophysical grids via EXPLORE Similar to the Forward Modelling tool Tutorial E2 Inversion also creates and stores summary results which can be viewed by going to Geophysics gt 3D Geophysics gt Results explorer The left hand panel provides a data explorer for all the cases you may have created The convention is to use GREE
31. 5750 0 4750 0 3750 0 2750 0 1750 0 750 0 250 0 8750 0 7750 0 6750 0 5750 0 4750 0 3750 0 2750 0 1750 0 750 0 250 0 Misfit 38 425386 lt v lt 24 967243 Observed_Magnetism_BuriedGranite 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m Misfit Regional Trend 38 425386 lt v lt 24 967243 Observed_Magnetism_BuriedGranite 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 67 Contents Help Top 4 Back gt 3D GeoModeller displays several grid images including calculated misfit grids The images are Top Left the observed grid Top Centre the computed response of the final inversion iteration Top Right the misfit or difference between the observed response minus the response of the litho model proposed in the final iteration Bottom Left is the result of choosing to solve and remove a regional trend No de trending is applied in this case Bottom Middle is same as Top Middle in this case Bottom Right is same as Top Right in this case Note that the colour scales are arbitrary and typically different for each of the images as they are the result of a linear colour mapping between the minimum and maximum values in the range for each grid 1 2 Toggle the Gravity data Ma
32. A Stratigraphic Pile Viewer Rela rence Top Senet 3 Onlap Loner Seres_2 Orlap Hoel rock Serres 1 Orlap Grane Save CSV Fie Fd Close 8 Next save the project with a new name in the folder you are using for your own tutorial materials It is important to progressively Save and Save As as you progress with the exercises From the main menu choose Project gt Save As OR From the Project toolbar choose Save As kJ OR Press CTRL SHIFT S Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 18 Contents Help Top 4 Back gt E1 Stage 2 Examine the project meta data Parent topic E1 Stage 2 Steps Tutorial El Ravinnthe 1 menu choose Project gt Properties existing geology ae Examine the project meta data For this project the dimensions and Coordinate System are e Projection _ Local Height Datum_ Local e Extents C Minimum Maximum Range fae Project Properties Name New_Project Version 1 0 Location 0D TEMP_PDAC_Tutorial_E TutorialE1 E1Beginning_Project Browse Authors Date 4 5 2005 15 25 49 Description Inversion Tutorial E Projection Local Unit im Precision Height Datum Local Dynamic Selection in Viewers Project Limits XMin 0 0 XMax 10000 0 YMin 0 0 YMax 10000 0 Min 2000 0 Max 0 0 ES Some furth
33. GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 1 Contents Help Top 4 Back gt Tutorial case study E Forward and inverse modelling of potential field data Parent topic User Manual and Tutorials Authors Phil McInerney Intrepid Geophysics Antonio Guillen BRGM Richard Lane Geoscience Australia Ray Seikel Intrepid Geophysics Helen Gibson Intrepid Geophysics Des Fitzgerald Intrepid Geophysics In this case study Introduction to Case Study E e Tutorial E1 Review the existing geology model Pages 15 23 Tutorial E2 Potential field forward calculation Pages 24 48 e Tutorial E38 Property optimization Pages 49 50 Tutorial E4 Prior only inversion Pages 51 52 e Tutorial E5 Joint gravity magnetics litho constrained inversion Pages 53 87 Tutorial E6 Forward calculation of full tensor gravity grids Pages 88 96 Introduction to Case Study E Parent topic Tutorial case study E Forward and inverse modelling of potential field data Contents Help Top Why are we interested in potential field data as an aid to geological mapping There are generally insufficient geological observations to unambiguously construct the boundaries between formations to form a 3D geological map Observations are generally in short supply at depth and relationships between formations may be unclear Variations in potential field response are related
34. Grad Ampilit OK Cancel You will note a number of 2D grids ers grid files 3D grids vo voxet files Also as we have used the FFT method rather than a spatial method a task file is also present that captures the process used to do the 3D FFT forward model This is typically called vfilt_GravityTensor task Geomodeller has spawned this separate process as a batch process 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 96 Contents Help Top 4 Back gt File Description calculated_GravityTensors_l ers 2D full tensor grid computed by FFT forward modelling 6 bands final_GravityTensors vo Resulting 3D grid 6 attributes one for each tensor component initial vo Initial 8D grid 2 attributes one each for Lithology density Observed_GravityTensors_1l ers empty grid as we did not use a supplied or reference grid vfilt_GravityTensors task The FFT process captured ready for batch or multi threading environments CONCLUDING NOTE This tutorial is currently under extension to include demonstration exercises of inversion referencing observed full tensor potential field data The functionality is in place and the GUI is fully enabled for this work Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt
35. ID1 FID2 Contents Help Top s Dist m Z Value C MID eigenvalue MIN eigenvalue C Ratio ie 12 11 C Strike ie atan I2 l1 C Octahedral Normal C Octahedral Shear C Cube Root Determinant Km Zoom In Square Root First Invariant C Scaled Moment gt JOON C Phase Zoom Previous C Modulo Mouse Mode Ai Query OK Cancel C Zoom or Trace You can slso examine the completed project folder as stored in your project directory GeoModeller tutorial CaseStudyE TutorialE6 Completed_project Case 3 Run1 Creating a FALCON tensor forward model The convention for a Falcon tensor grid comes from wishing to preserve the same 6 band BIL scheme that is used for FTG while indicating in a systematic way that the data is reflecting the duplicate A and B readings of the horizontal tensor gradient that is the Falcon s signature The spreadsheet tool in Intrepid has a simple function to convert the FTG forward model grid created above into a form that is compatible with an observed Falcon tensor grid This process must be followed before proceeding to any visual comparison of an observed Falcon gridded dataset and the response from your model The options for visualizing a Falcon tensor grid are also adapted to what is available from the measured data Tensor Query Options for Tensor Grid Dataset Falcon options A t B OC Average C UY ie HY ie Y C MAX eigenvalue C Difference OCO MIN eigenvalue tC Phase tC Curve
36. N arrows to indicate Forward model result cases and RED arrows to indicate inversion cases The other main function available here is the ability to delete cases that are of no further interest Forward Viewer D TEMP_PDAC_Tutorial_E TutorialE5 E5Completed_Project inversion xml File Help Contents Help Top case1 Q Case2 Common parameters iran Gravity data Magnetic data an Observed 34 394973 lt v lt 57 975132 Observed_Magnetism_BuriedGranite 8750 0 7750 0 6750 0 5750 0 4750 0 Y m 3750 0 2750 0 1750 0 750 0 250 0 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m 20 20 7 o 20 0 s 50 Regional Trend 0 0 lt v lt 0 0 final_ Magnetism_2 8750 0 7750 0 6750 0 5750 0 4750 0 Y m 3750 0 2750 0 1750 0 750 0 250 0 4 X m Regional Settings Computed 13 136177 lt v lt 50 44141 Y m Y N i rs Y Computed Regional Trend 13 136177 lt v lt 50 44141 Y m 8750 0 7750 0 6750 0 5750 0 4750 0 3750 0 2750 0 1750 0 750 0 250 0 8750 0 7750 0 6750 0 5750 0 4750 0 3750 0 2750 0 1750 0 750 0 250 0 final_Magnetism_2 Y m 250 0 1250 0 2750 0 4250 0 5750 0 7250 0 8750 0 X m final_Magnetism_2 Y m X m Degree 0 Constant w Regional 0 Apply Solve 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 8750 0 7750 0 6750 0
37. Standard deviation is half the range in other words the limits of the distribution are Mean value Standard deviation A Poisson distribution is completely defined by the Mean value in other words the Standard deviation is not required An Equal Plus distribution is an equal distribution where the Mean value is the minimum value and the Standard deviation is the range An Equal Minus distribution is an equal distribution where the Mean value is the maximum value and the Standard deviation is again the range At present the properties are initialised when performing either a forward or inverse Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 28 Contents Help Top q Back gt calculation using the mean value This is the reason for having three different ways of defining an equi probable distribution that is where the distribution is defined with a mean that relates to the central minimum and maximum values respectively for the equal equal plus and equal minus distributions Supply Density values in units of g em Supply Magnetisation values in SI units We assume that the magnetisation is entirely induced 3D GeoModeller obtains the orientation from the ambient field information 1 cgs or emu unit of susceptibility 4 z SI units of susceptibility ma
38. The mapping module is used to compile boundary and orientation information into a 3D map that shows the geometrical arrangement of boundaries between the formations Physical property measurements are assigned to formations and statistical methods are then used to determine the characteristics of these properties at the scale of the elements used in the inversion phase Overall strategy Parent topic These tutorials guide you through practical demonstrations beginning with a forward Introduction to modelling exercise and progressing to a litho constrained joint inversion of gravity Case Study E and magnetic datasets Put simply see illustration below the idea is to begin with a starting 3D geology model that honours all geology observations somewhere in green space Then use the observed gravity and magnetic data sets to drive an inversion result to deliver only 3D geology models which also honour the gravity and magnetic data 1 e in the Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 4 Contents Help Top 4 Back gt overlapping space between red green and blue 3D GeoModeller uses the principles of statistical sampling to drive the inversion process so the approach can be thought of as a Monte Carlo Markov Chain simulation For more details see Forward modelling and inversi
39. Top lt 4 Back gt 20 A report on the importing of points 1s given Information Formation Fault Description Points Imported NEWgranite Formation Fault 95 Total 95 0 entries ignored 10 outside Project Bounding Box 10 entries unmapped 21 From the Main menu View gt 3D Viewer gt Show interface data cic 0E ort Export Window Help A 4 20 Viewer G h OA EE Y Ro B 30 Viewer 14 Show Interface Data Ed amp S Show Orientation Data Vertical Exaggeration iW Show Drillholes Formations Edit All Appearances Load Surface Mesh Dykes Edit All Appearances Faults Edit All Appearances Show Information HUD Presentation Background Colour Bo Wao Point Acquisition Parameters le 2 Points List Visualisation Save Image As Select NEWgranite gt OK n P Show Interface Data in 3D To show geology interface data in the 3D Viewer select the Formations and Faults that you wish to display and press OK or Apply Geology Data E Cover f i l i Select All Deselect All Invert i Parameters i Radius 141 421 m Thickness 70 711 m Ez unG inlets aE The points viewed below define the top of the MostProbable granite body as an outcome of the joint geophysical inversion 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E
40. TutorialE2 Data Observed_Magnetism_BuriedGranite ers gt Open Ensure a grid is registered for both Fields check by toggling between Gz and TMD Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 56 4 Back gt 3 Create Inversion Case Model Settings Voxet Extent Fields to Compute 4 Gz Vertical Gravity Gravity Tensors TMI Total Magnetic Intensity Magnetic Tensors Mx Xmin 0 Xmax Ymin 0 Ymax Zmin 2000 Zmax 10000 dX 500 nX 20 10000 dY 500 nY 20 gt 0 dz 100 nz 20 Observed Grid TMI Total Magnetic Intensity Observed Grid bserved_Magnetism_BuriedGranite ers Modelling Uncertainty 0 1 Match Trend Degree 1 Rate 0 Output Trends Observation Surface Constant elevation 0 Drape gt Terrain dearance Drape gt Load from dataset Vertical sampling interval 100 Memory requirements 1MB 12 Leave the other options as defaults and choose NEXT Before leaving this page note extra options available e Detrending the observed gravity grid Specifying the elevation surface to calculate the on going response on exactly the same as for Forward modelling e Specifying a vertical sampling interval on the topograph
41. User Manual Tutorial case study E Forward and inverse modelling of potential field data 15 Contents Help Top 4 Back gt Tutorial E1 Review the existing geology model BuriedGranite Parent topic In this tutorial Tutorial case study E e E1 Introduction Forward and inverse modelling of potential field uati e El Stage 3 Re compute and review the 2D and 3D views of the geology model E1 Introduction This simple 3D GeoModeller project model has already been created for you E1 Stage 1 Load and examine the BuriedGranite GeoModeller project E1 Stage 2 Examine the project meta data In this tutorial we will explore the existing 3D geology model using menus for viewing the project properties geolgical editing and visualisation without making changes to the model E1 Stage 1 Load and examine the BuriedGranite 3D geology project model Parent topic E1 Stage 1 Steps Tutorial El Review the ui geology 4 Launch the 3D GeoModeller software to reveal the splash screen H diardi nada Emit ate e ata aeda eA ani mid Aa a WaGSGaiw se xvoevi weer all Baog adle o a View the pre created 3D geology project in 3D GeoModeller u a S o UE See ee E 2 From the main menu choose Project gt Open OR From the Project toolbar choose Open amp OR Press CTRL O 3 Browse to the pre created 3D GeoModeller project GeoModeller tutorial CaseStudyE TutorialE1 E1lBeginning_ P
42. al observations Have a physical property distribution close to what you have assigned and e Obey the geology tests Next you will use a number of tools to visualise and analyse the inversion results These enable Viewing of the misfit evolution curve e Running of the super summary statistics collation amp analysis tool after first deciding the burn in point or earliest point of convergence during inversion Loading directly viewing and accessing the intial final and post SuperSummarystats output MeshGrids results voxet 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 14 Contents Help Top 4 Back gt Filtering slicing combining and computing with the MeshGrids results voxet as required For example To create histograms of the mean amp standard deviations of rock properties from the accepted proposals considering every single voxel cell grouped on a per lithology basis this could either be from the final iteration or say from all accepted proposals between burn in and the last iteration 9 Forward calculation of the gravity full tensor response using a Fast Fourier Transform in 3D Also visualisation of the component tensors Tutorial E6 Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller
43. appear on wizard pages 3 amp 4 E5 Steps overview 1 Set up the new Case and Run number select observed geophysical datasets Check associated physical property distributions for each formation Set the exploration bounds on geology boundaries to be explored during inversion Set iterations boundary conditions and the aspects of lithology that will be fixed o FF GW N Carry out a stochastic simulation exploring all allowed bounds of the geology gravity and magnetics data sets 6 When 3D GeoModeller has finished a misfit trend can be analysed to see the progression towards converged solutions You judge this by observing where the misfit becomes more or less constant despite best efforts to perturb the model 7 For the proportion of the inversion runs where the misfit was constant begin at Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 54 Contents Help Top 4 Back gt the burn in point request a Super Summary Stats voxet to be created This included all the results of the valid models of the simulation but excludes the beginning iterations before burn in 8 Next we view the final calculated geophysics grids the statistically compiled gveophysical results voxets the per lithology rock property distributions and thresholded surfaces of probabilit
44. ar A background or regional density can also be set Leave the reference density and above topo density as the defaults both 2 67 3 Create Forward Case Lithology Physical Properties Type Formations Property Value Me Cover E Gravity mn Density Log normal 3 1 0 1 70 Normal 2 9 0 1 30 General 7 Indude Border Effect Reference density Above topo density lt Back Next gt Choose NEXT as prompted to launch a Spatial method forward computation Note on the last page you are prompted for the number of CPUs to commit to this task You also have the option for an interactive session or a batch session in the background In this case the time to compute 1s small so interactive is OK 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 36 Contents Help Top 4 Back gt Choose FINISH Runtime Settings Monitoring the forward calculation Information The program discretises the geological model extracts the lithology at the centre of each cell To make the forward model calculations tractable especially as 3D GeoModeller uses the forward model calculation many millions of times during inversion we must discretise the geological model This means that we need to convert the continuous form of the geological model created in the mapping m
45. ation Manager T Grids and meshes T 2 calculated_Gravimetry_1 gt Appearance a r calculated_Gravimetr is Edit Colours and Clips Display color table Z Contouring id Histogram Visual Filter id Gutenberg Richter Plot Polynomial approximation Cross plot with Ere Multi crossplot with Multifield analysis Delete amp Properties 6 Check the Field Visualization Manager Also you can see all available mechanisms for displaying colour table matching statistical analysis cross plots contouring and general manipulation of fields within any grid or surface Special purpose geophysical options are also available for micro seismic analysis Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 41 Contents Help Top 4 Back gt 7 Check View on section for MNT Grid Sections view Sections View on section View on Section in 30 Contours on Section Contours on Section 30 Parameters i Display color table Contouring Edit Colours and Clips e E pue m The calculated grid of gravity is now geolocated in the 2D map section of the current geology model Note the observed_Gravimetry_1 can be loaded in addition Repeat steps 5 6 and 7 above Toggle between different 2D grids on the
46. avimetry_1 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 SUOIEAASO JO JaquUiNN Statistics Property Value n Total 400 n Effective 400 n Nulls 0 Nulls 0 Min 6 142409 Max 18 44286 Mean 7 619738 Std Deviation 5 574406 Kurtosis 0 275256 Skewness 0 799628 Variance 31 073998 ALL v You can also examine the completed project folder to view the grid files directly as stored in your project directory Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 43 Contents Help Top 4 Back gt GeoModeller tutorial CaseStudyE TutorialE2 Completed_project C asel Runl Description Observed _Gravimetry_1 A copy of the supplied grid 3D GeoModeller may have resampled the observed grid and trimmed its extent if the supplied grid was not wholly within the plan view extent of the current project calculated _Gravimetry Response grid of the starting geology model using 1 the density values set in the physical properties table 3D GeoModeller writes results from the forward model calculation to standard ERMapper geophysical grids Load the initial lithology amp density 3D voxet and view histograms The process of running a forward model requires that a Case or initial lithology voxet is created at the c
47. bution 0 1 Pr TES NO ested each geophysica dataset End af Run YES ore proposals to YES consider Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 13 Contents Help Top Overview of steps for this case study Parent topic Introduction to Case Study E Contents Help Top q Back gt Review the existing geology model Tutorial E1 1 To understand the geological scenario and familiarize ourselves with the starting geology model you will load the already built 3D geological project without making any changes Using the menus for geological editing and viewing you will explore the geological data constraining the model repeat the model compute run the 3D interpolators to build surfaces and visualise 2D and 3D aspects of the model and geological pile Forward modelling Tutorial E2 2 Firstly associate physical property distributions with each geology formation required for both forward and inverse modelling Next carry out a gravity forward calculation using a spatial method to see whether the combination of the geological model and the choice of physical properties produces a response that broadly corresponds with the measured geophysical observations Access a results viewer then also view the geophysical response grid
48. cagno P Lane R Lees T and McInerney P 2004 Constrained gravity 3D litho inversion applied to Broken Hill Extended Abstract ASEG 17th Geophysical Conference and Exhibition August 2004 Sydney 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 3 Contents Help Top q Back gt Lajaunie C Courrioux G Manuel L 1997 Foliation fields and 3D cartography in geology principles of a method based on potential interpolation Mathematical Geology 29 4 571 584 Forward modelling and inversion with 3D GeoModeller a 3D GeoModeller reference manual Interpretation phases Parent topic The flowchart shows the basic phases for production of an integrated interpretation of Introduction to _ geological physical property and geophysical data Operations that you can carry out Case Study E i using 3D GeoModeller are shown in cyan Gegagica Physica property Leon sical observations Measurements observations Geometry ol Histogram amp Pre process gnc formation spata comelaion continue to plane Preliminary compiled into a 3D determined tor upward continue interpretation each formation remove regional inversion Inversion Integrated Interpretation Following acquisition geological observations are assessed and assigned to categories formations
49. ck on the Grids and Meshes item or from the main menu open the Import gt grid and mesh gt 2D grid oe 7 bes ET Drillholes f 3D Geology El JB serie F1 Wl Grids ar 1 DESE ES a Meshes and grids O No meshes or grids Create grid with zero walue field Import Grid or Mesh pees es se 3D Grid Voxels Triangulation al eS Observations ASCI Observations i 2D Grid 3 Browse to TutorialE2 gt Completed_Project gt Case1 gt Runt For this E2 training exercise the file to load is calculated_Gravimetry_1 ers 4 Ensure your 2D section called MNT is open and active green tick will show Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 40 Contents Help Top 4 Back gt wa Gplre i Wc aLe seal 3 GS New Project P Formations en TH Dykes H ii Faults z is Drillholes H 3D Geology 5 fg Grids and meshes Sje z calculated _Gravimetry_i i 7 r calculated_Gravimetry_1 5 Expand the symbol which has appeared next to Grids and meshes in the Explorer until you can select and then right click on calculated_Gravimetry_1 qi calculated_Gravimetry_1 wf is MNT 3 amp GE MA Drilholes J Hide all views of this field H 30 Geology a Field Visualis
50. d results and settings captured between 400 000 amp 500 000 iterations ie Summary Statistics from Inversion Result Case Runi 47 4 6 45 445 43 42 4 1 4 0 a9 a8 a7 fale m 3 6 35 34 33 3 2 3 1 100 000 150 000 200 000 250 000 300 000 350 000 400 000 450 000 500 00 Iterations Joint Gz TMI From 400000 To 500000 Threshold 30 aff OK Fd cose Note that we left the default Threshold at 90 This 1s a percentage measure of geological uncertainty to be recorded in the statistical summary See E6 Stage 7 below and the Table therein for further details When the Summary Voxet calculations are finished you will see the following pop up Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 65 Contents Help Top 4 Back gt Information The Voxet oD TEMP_PDAC_Tutorial_E TutorialE5 ESCompleted_Project Case2 Runl SummaryStats_400000_500000_Threshold_90_super vwo has been created and ts available for Import View the list of your joint inversion output files Here is a summary of the inversion output files which now exits in your project directory folder Case2 gt Runt File s Description misfit csv Numeric rec
51. d Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 37 Contents Help Top 4 Back gt We create these copies by reflecting the model about the vertical sides of the model and performing a double reflection to produce the corner tiles This strategy results from the thought that the region adjacent to the volume under consideration is most likely occupied by material similar to that of the model volume 3D GeoModeller calculates the forward model response of the entire padded model at grid points above the core model volume This simple strategy reduces the need to remove the effect of sources adjacent to the model volume However we still need to exclude the response of material below the model volume from the observed data before comparing these data with the forward model response Lateral padding of model Plan view of i j Lie lu Me k Plan view of padded litho model arrangement used in the forward model response calculation Summary images of the response for gravity forward calculation 3D GeoModeller displays the images of the response of our gravity forward calculation in the Results Explorer window 1 To remove a DC shift or regional trend from your calculated response go to the bottom left hand corner select a degree from the regional settings available O Constant is a DC shift 1 linear is the
52. d data 82 q Back gt 17 Step 3 of 4 Sorts the columns Geological Formation Project NEWeranite X A Y B Z C gt Next fm CSV Data Import 3D Interfaces Steps Map CSV colums to data structure Step 3 of 4 Parse CSV file Map CSV colums to data structure Map geologic objects in project data 2250 000000 2750 000000 1500 000000 2250 000000 3250 000000 1500 000000 2250 000000 3750 000000 1500 000000 2250 000000 4250 000000 2250 000000 4750 000000 2250 000000 5250 000000 2250 000000 5750 000000 2750 000000 2750 000000 2750 000000 3250 000000 2750 000000 3750 000000 Auto EA EC Ce Reset g Y bagl bad Rie kai ba Fa bad Ld ha of 18 Step4 of 4 Lastly merge to existing Formation called NewGRANITE green 19 gt Finish Map geologic objects in project data Step 4 of 4 Geological Objects Mapping structure Map geologic objects in project data Merge To NEWoranite NEWoranite Do not import Import Create Formation Create Fault Merge to Existing Formation Merge to Existing Fault 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt Contents Help Top GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 83 Contents Help Top Contents Help
53. e statistical arrays for densities and magnetic susceptibilities e Load the SummaryStats voxet and visualise most probable geology Visualise most probably thresholded geology Load the final voxet 3D grid to the 3D geology workspace 1 From the Explore tree select Grids amp Meshes 2 Right click Import gt 3D Grid Voxels 3 Browse to and Open final vo in your results directory For example CaseStudyE TutorialE5 E5Beginning_ Project Case2 Run1 final vo amp Explore lem C2 alias New Project m E Formations ee it Faults P E sections W Drilholes 2 30 Geology g a Meshes and grids J Hide all views Create grid with zero walue field Import Grid or Mesh lb Intrepid Mesh or Grid Delete uy 3D Grid Voxels Triangulation a Observations ASCI Observations 2D Grid L ma Recent Items Desktop E My Documents n a final wo A initial wo 7 reference vo 7 SummaryStats_ 400000_500000_Threshold_90_super wo Computer a File name gt Tutorial_E TutorialES E5Completed_Project Case Run1 Network Files of type All Acceptable Files Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 70 Contents Help Top 4 Back gt 4 Inthe Explore tree a symbol
54. e the Model Interpolate Geology and Structural Da Geology and Structural Data Faults to Interpolate 10000 m Use Points 10000 m Use Points Use Points ey Project Zone Explore the 3D Viewer Build the model in 3D 3 From the Model toolbar choose Build 3D Formations and Faults Build 3D Formation and Fault Shapes 3D Shape Parameters Type and Mesh Resolution Build Formations Faults Type Volume I coum amp Surface Draw Shapes after Building Resolution 9 Low Medium Render Quality More In the Build 3D Formation and Fault Shapes dialog box Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 87 Contents Help Top 4 Back gt Check Build Formations Check Build Faults Select Type Volume Check Draw Shapes after building Adjust the Resolution Render quality to Medium 4 Choose OK The full model in built in the 3D Viewer but let s now reveal the NEW granite 5 From Explore gt Expand the 3D Geology 6 Expand Series3 gt Volume Cover gt Hide 7 Expand Series2 gt Volume Host_rock gt Hide 3D View D E oes DOR x 2000 NY 4no0 N 4000 2000 N Conclusion the inversion outcomes for the NEW granite body are now fully integrated in the re
55. ea All six tensor components will automatically select too Use Project Use Lithology Voxet New case name Fields to compute The six separate components of the Gravity Tensors Select the components to calculate during forward modeling tutorial CaseStudyE TutorialE6 E6Beginning_Project E6Beginning_Project xml Case3 0 Create a new case Clone an existing case Gz Vertical Gravity Gravity Tensors Gxx Vlcy Gxz WwiGyy Gyz Gz CITMI Total Magnetic Intensity Magnetic Tensors Mx CM Mz Myx of oka E Saa Gxx second derivative of the gravity potential purely in the x east direction Gxy or Gyx second derivative of the gravity potential in the composite directions x and y Gxz or Gzx second derivative of the gravity potential in the composite directions X and z Gyy second derivative of the gravity potential purely in the y direction Gyz or Gzy second derivative of the gravity potential in the composite directions z and y Gzz second derivative of the gravity potential purely in the z depth direction 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 90 Contents Help Top 4 Back gt NINE COMPONENTS OF GRAVITY GRADIENT TENSOR Gxx Gyx Gzx Gxy Gyy Gzy Example Gxz Gyz Gzz Gyx Gxy
56. ell size defined in Create Forward Case gt Voxet Properties See page 34 Other attributes of the initial case are stored in the same voxet such as densities The voxet files can be viewed directly in Windows in the path containing your tutorial project TutorialE2 Completed_Project Casel run1 initial vo 1 In Explore choose Grids and meshes and click right 2 Choose import gt 3D Grid Voxels 3 Browse to TutorialE2 Completed_Project Casel run1 initial vo i Explore YQ New_Project P Formations ah Dykes i Faults i Sections iW Drillholes 30 Geology gi j and h Pi i Grids mnd manhan yy Meshes and grids ate an aia MNT kj Create grid with zero value field Import Ie 20 Grid Delete SS 3D Grid Voxels gt 2D 3D Observations al Triangulation 4 In Explore an expandable voxet item Initial will appear and will further reveal Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 44 Contents Help Top fie Histogram of Lithology Volume Geological Model 100 Lithology Volume m3 95 Cover 5 3975E10 0 Host rock L22211 Granite 2 31E10 BO 4 75 704 65 m 61 462 B 604 u 55 5 N 50 Ea U 45 a D 40 al 35 MU 26 988 25 204 S 15 11 55 10 S U Granite Host_rocl Covel Lithology Ss C
57. ely different distribution to the observed response The average starting mis fit is more than 200 mGal and far too much to consider inversion sot Anh 200 400 Left is observed right is calculated units in mGal 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 9 Contents Help Top 4 Back gt Taking the example case here of having an observed gravity grid and a forward model of the gravitational response from your model above figure you should immediately examine the two grids for a spatial comparison and also on a statistical basis In the case shown the likelihood of your starting position migrating to the required observed position while also honouring the known constraints 1s very low One extra complication here is the issue of detrending a regional response What this can mean is that your observed grid of geophysics data contains a contribution from a much larger and deeper volume than what you are modelling You can either high pass filter your grid to remove a regional or allow geomodeller to detrend the observed grid in an automatic way thus also removing the regional By analogy it is very important to build an initial 3D geology model that 1s as close as possible to the real situation To check this forward modelling of the gravity and magnetic responses of your initial
58. er comments about the 3D GeoModeller project work space e X Kast Y North and Z Elevation positive upwards are a standard coordinate framework according to a right hand rule gt X Y Z are all in the same units meters they cannot be degrees of latitude or longitude e Xand Y would typically be real world projected coordinates but could be a local grid this is the case for the BuriedGranite model e Zis elevation and is positive upwards It also would typically use a real world vertical datum such as mean sea level e You can and should define the Projection actually a Coordinate System consisting of a Datum and Projection Geolocation of your project is essential if you are to properly create and integrate with geoscientific data from many sources Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 19 Contents Help Top lt 4 Back gt All data must be within the 3D project limits Data outside of the limits will be ignored when importing a report will be given listing them as excluded e Likewise all modelled results geology lines polygons and surfaces reside within those limits When you create your own project make the project dimensions large enough to e include all your data include a margin above your highest point of your topog
59. erence Velocity Vp 1500 of 0K Fd close 3 Now choose Geophysics gt 2D geophysics 4 At the top choose section C2 as this will be the vertical section on which to show a predicted seismic response 5 Toggle to the Seismic tab The Physical Properties status is shown as Defined 6 The Time Space and Frequency sampling parameters allow you to adjust the resolution of the predicted response Change the From Frequency sampling to just 2 Hz 7 At the top tick Compute Seismic and 8 atthe bottom select Compute The following results pop up shows the section C2 through geology model together with its 2D synthetic seismograph 9 Finally Save as Image Example name C2 seismic in Case 1 Run Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 48 Contents Help Top 4 Back gt Seismic on C2 iofi amp Seismic cross section X m 0 600 01200 0 2400 0 3600 0 4800 0 6000 0 7200 0 8400 0 9600 0 0 253 3 506 7 760 0 Time s 1013 3 1266 7 1520 0 1773 3 mmm 0175 0150 0125 0100 0075 0050 D025 0 000 o o 0o75 Amplitude Geology Cross Section Depth m 600 01200 0 2400 0 3600 0 4800 0 6000 0 7200 0 8400 0 9600 0 Distance m Cover W Granite H
60. erminant function and some basic statistics The images are e Top Centre the response of the current model that you have calculated Top Right the current misfit meaningless without an observed grid e Bottom Middle is the computed response no detrending applied Bottom Right is the redone misfit plot meaningless without an observed grid It is not applicable to alter the Region Settings or detrend as no observed grid is available for comparison in this case Note that the colour scales are typically different for each of the images as they are the result of a linear colour mapping between the minimum and maximum values in the range for each grid 1 Use File gt Exit to leave this tool 2 Project gt Save All grids are saved in a folder within the GeoModeller project folder called Case3 E6 Stage 3 Visualisation of the component tensor grids Viewing one of the tensor component grids requires dynamic re sampling of the full tensor grid This 1s done using Spherical Linear Interpolation SLERP along the rows and down the columns As you zoom into an area of interest the full tensor is calculated at all points The required component is then passed to the view window 1 Open Geophysics gt Examine Geophysical Grids 2 Open File gt Load Grid Dataset D Intrepid Visualisation J ago File Line Display Point Display Grid Display Polygon Display Window Help Load Line Dataset GRID Load
61. etic tab note that the Total field nT Declination and Inclination are default values This is due to a local co ordinate system being set in this project see Main Menu Project gt Properties A real world co ordinate system for the model would result in appropriate fields being automatically filled here Just provide the date of the observed geophysics survey using the IGRF calculator and these will adjust accordingly Alternatively you can manually enter the Total field nT Declination and Inclination from independent sources No changes to be made here yet Set single mode mean magnetic susceptibility properties Steps 1 Inthe menu tab for Magnetic gt Susceptibility SI double click on the value field Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 26 Contents Help Top 4 Back gt for Cover to display details of the current magnetic susceptibility for Series3 Cover Enter change them to the values below Series Mean Standard Statistical Percentage of Susceptibility Deviation Law Population ie Susceptibility Susceptibility Law Definition Definition of the mode component Parameters Mean 0 00002 SI Modes Standard deviation 0 000001 Mono modal Bi modal Statistical law Tri modal Peet Normal Log normat Equal Poisson Equal Plus Equal Minus
62. ey observations Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 72 Contents Help Top 4 Back gt E5 Stage 8 Analyse 2D amp 3D composite views of resulting geology geometry 1 From the Explore tree select Grids amp Meshes 2 Right click Import gt 3D Grid Voxels 3 Browse to and open final vo in you results directory CaseStudy E TutorialEK5 E5Beginning_ Project Case2 Run1l Summarystats _400000_500000_Threshold_90_super vo 4 Select SummaryStats_400000_500000_Threshold_90_super vo Look in t he bis Recent Items Desktop E final vo a initial wo E reference vo a SumrmaryStats_400000_500000_Threshold_90_super vo TS File name gt Tutorial_E TutorialE5 E5Completed_Project Case2 Run1 Open a Files of type All Acceptable Files Cancel 5 In the Explore tree a symbols appears next to the Grids and Meshes expand this directory twice to reveal 12 different property fields of the attributed 3D grid Explore S GR New_Project g J Formations g bt Faults n a Drillholes g 3D Geology Sia Grids and Meshes g ea Observed_Gravimetry_BuriedGranite ee we SummaryStats_400000_500000_Threshold_90_super bss 14 ChangeCount EE Entropy Ml MeanDensity bo EN lt tdDevDensity bo TE MeanSusceptibil
63. gnetic data menus to show similar summary images for Gravity Use File gt Exit to leave this tool All grids are saved in a folder within the GeoModeller project folder called Case2 Load the 2D geophysics grids observed amp final to the 3D geology workspace A N S 8 Contents Help Top Ensure your MNT Section is open in the 2D Viewer From the Explore tree select Grids amp Meshes Right click Import gt 2D Grid Browse to CaseStudyE TutorialE5 E5Beginning_Project Case2 Run1 final_Gravimetry_ l ers In the Explore tree Expand the for final_Gravimetry_l ers with the grid selected right click Field Visualisation Manager Tick MNT versus View on Section i 3P Iso values 2D Grid Sections View Sections View on Section View on Sectionin 3D Contours on Section Contours on Section 3D All MNT v Parameters Display Color Table Contouring Edit Colours and Clips e a Eda Display Colour Table gt OK The grid will immediately geo locate in the MNT 2D 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 68 Contents Help Top 4 Back gt Viewer AND display the Colour Table Or Click on the same grid in Explore and right click gt Display Colour Table vam BN x MA Drillholes 2D Geology Wa Grids and Meshes Ee 4 Ob
64. gnetisation susceptibility x field_intensity H magnetisation susceptibility x induction B uo Hence if you know the susceptibility suse in SI 10 and the ambient field amb in nT then the magnetisation 1s susc 10 amb 107 4 rn 107 Multi modal options The multi modal options enable you to define complex distributions as a random mixture of samples from populations that are defined by simple uni modal distributions Specify the proportions for each mode Since these are constrained to add up to 100 3D GeoModeller automatically assigns the proportion of samples for one of the modes based on the proportions specified for the other modes Set bi model mean density properties Steps Parent topic E2 Stage 1 Enter physical properties Contents Help Top Create a bi modal distribution with 70 30 proportions 1 In the Gravity gt Mean density properties dialog box for Host_rock select Bi modal from the Modes option buttons Set the parameters as shown in this table Components Mean Standard Statistical Percentage of of series 2 Density Deviation Law Population 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Contents Help Top Contents Help Top Description Unit g cm Log normal 3 1 0 1 70 Norm Definition of the mode component Definition of the mode component
65. gy tests limit totally random variations to the initial geology model In 3D GeoModeller five inversion control commands are currently provided in respect of varying the geometry of geology units in the initial or reference model These are Movable Commonality Commonality Volume Shape Ratio and Volume Ratio From previous studies it has been found that in most cases Commonality and Shape Ratio are the only commands typically required to launch a robust inversion This tutorial demonstration 1s no exception NOTE You will need to choose each Lithology unit in turn when applying the geology tests A highlight box is drawn around the chosen unit Starting from the top right hand side 3 mechanisms are available per lithology Fix lithology frontier basically freeze the geometry of this unit you might have good near surface seismic control of this layer e Constraints to modify the rules for how a lithology unit s shape and volume is confined as it changes with successive proposals Note these are the test settings the test on off buttons are later in the RUN page of the wizard gt Always above these lithologies also known as Preserve Younging Direction Allows disallows overturning of the younging direction in your geology sequence This requires your geological knowledge but is often known For example Thrust faulting is absent in our Basin Setting hence units will always appear in depth order as per the stra
66. here may be many millions of models involved We use statistical methods to distil and simplify the information contained within these models It is important to recognise the difference between statistical entities such as the most probable model from the models that were actually sampled during the inversion The statistics highlight general features of the samples but do not necessarily represent a true configuration of lithologies and properties Physical properties Parent topic Introduction to Case Study E Contents Help Top It is unrealistic given our knowledge of the real world to assign a single constant physical property to each geological formation It is also well known that the bulk properties of rocks vary considerably from those measured in a laboratory on a small scale or say from a sample gathered in a borehole We tend to measure the properties of the most durable portion of the population and ignore the more friable fraction Every formation shows some degree of heterogeneity We simulate this in the inversions by defining a distribution or spread of physical properties for each formation Our convention for recording the spread is to ask you to define a probability distribution function or PDF In the simplest of cases this can be a Normal population with a mean and standard deviation In a forward model the mean is adapted for the single run Before spending time on inversion we recommend you
67. hysics can be interpreted through forward and inverse techniques as demonstrated in this tutorial then the starting geology model will be driven toward the reality and better matches to the observed geophysics will be possible Select Specify an Observed Grid Browse for and load the observed Gz grid file GeoModeller tutorial CaseStudyE TutorialE2 Data Observed_Ground_Gravity_BuriedGranite ers Choose a calculation surface that best describes the same surface as your grid of observed responses Choose Constant elevation 0 m This assumes the data 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd lt 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 33 Contents Help Top lt 4 Back gt was collected on a constant elevation which is on the zero height datum eg sea level This will ignore terrain effects in the response Alternatively you can create a calculation surface which mimics the shape of your DEM but for a set terrain clearance height The final option allows you to load an external drape grid that you want your model response estimated upon This is the closest option to being able to compare your model response calculations to what might be given to you from an airborne geophysics contractor grid Choose NEXT f p anA Forward Case Forward Model Parameters Set parameters for field 1 of 1 Gz Ob
68. iate to shapes not properties The advantage of Weibul is that it is a very conservative PDF The probability of a radical change at any one step is minimized whereas for a Normal distribution there is always a 50 50 chance of a larger change 3 For Granite leave Volume Ratio on the default value of 0 25 0 25 equates to 75 of the volume stays the same as the reference model By definition Volume Ratio is the extent to which the total volume of a formation s voxels remains the same as the total volume of that formation s voxels in the reference initial model Both of these laws are explained in detail in the Reference Manual Forward modelling and inversion with 3D GeoModeller v2 2012 4 Choose Next Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 62 Contents Help Top 4 Back gt E5 Stage 4 Enter run control parameters Here you control the specifics of the inversion run number of iterations how to influence convergence and switches for geology constraint tests set but not on yet Create Inversion Case Run Settings Iterations sooboa Geological Likelihood Criteria Allow Formation Geometry Tests Y Allow Commonality Test none Allow Shape Ratio Test none Indude Above Topo Faces in Shape Ratio Include Outside Topo Faces in Shape Ratio Allow Vo
69. ift added e Bottom Right is the redone misfit plot to see if this extra regional has improved the misfit to the observed Note that the colour scales are typically different for each of the images as they are the result of a linear colour mapping between the minimum and maximum values in the range for each grid 3 Use File gt Exit to leave this tool All grids are saved in a folder within the GeoModeller project folder called Casel 4 Use Project gt Save 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 39 Contents Help Top 4 Back gt You can return at any time later to see these results again by going to Geophysics gt 3D Geophysics gt Results explorer The left hand panel provides a data explorer for all the cases you may have created The convention is to use the GREEN arrow to indicate Forward model result cases and RED arrows to the left to indicate inversion cases Analyse the forward calculation Steps Parent topic E2 3D GeoModeller saved the results of the forward gravity calculation in the project ais folder in Case1 gt Runt You can examine the grids in more detail by viewing the files orwar calculation Load 2D grids to 2D sections of the geology model 1 Back in the 2D viewer of the main GeoModeller workspace go to the Explore Window 2 Left cli
70. ill core or hand specimen measurements 1s averaged out when considering the variability between samples having large volumes This issue of estimating the variability between samples with different volumes is analogous to the problem of estimating the grade for a mine stope from assays of drill core samples The variability in the grades for stopes is always much less than the variability observed in small volume samples Unfortunately it is very difficult to estimate the correct variability spread of values for specifying in 3D GeoModeller without measurements from a large number of samples from many locations within the project area However if you have some confidence in the volumes of the main units Property optimization E2 can help Prior geological information Parent topic Introduction to Case Study E Contents Help Top Prior to commencing forward or inverse modelling methodical investigation of all available datasets 1s crucial to building a realistic starting 3D geology model The following illustration shows progressive investigation of gravity and magnetic data via a range of interpretation methods In combination with all available geological observations surface and sub surface completing some or all of these methods can provide best available knowledge for building your starting 3D geological model 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial ca
71. ints middle 4 sections Leave defaults for Cover and Host_rock e Constraints middle 4 sections For Granite we want to maintain the integrity of this proposed 3D intrusive but need to allow it to shift and expand more than the Cover or Host_rock units These requirements are met by setting For Granite set Commonality to a Weibull PDF of 0 4 by clicking on the pencil at the right hand side 0 4 equates to 70 similarity with the reference model that is more freedom than the default of 0 2 which equates to 84 similarity with the reference model By definition Commonality is the extent to which formation voxels remain tn common with that formation s voxels in the reference initial model Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 61 Contents Help Top 4 Back gt 3 Definition Description Definition of the mode component simulation Parameters roof A Scale Shape Statistical law Rayleigh Weibull Log normal ga 05 10 14 20 25 30 35 40 45 EI Weibull 0 4 1 0 100 a EETTE a 2 AN gt b E Pay a O Qi 100 80 60 40 20 0 same as the reference model Viewing modifying the Weibull PDF is the same as for lithology properties except there is no provision for multi populations The PDF s you choose are appropr
72. ion Case 3 Model Settings Voxet Extent Xmin 0 Xmax 10000 dX 500 nX 205 Ymin 0 Ymax 10000 dY 500 nY 205 Zmin 2000 Zmax 0 dZ 100 nZ 20 Fields to Compute Observed Geophysics Grid Gz Vertical Gravity Observed Grid Gravity Tensors ling Us Gxx Gxy T Gxz Gyy te Gyz Gzz TMI Total Magnetic Intensity Observation Surface Magnetic Tensors Mx Dra T f My Dyr Mz i Mxx e Mx y i requir B Mxz Myy Myz Mzz Now we can choose voxet extents and cell size for the discretisation scheme of the Case For a rapid inversion accept the defaults The defaults are the geology model project space with a relatively coarse voxet cube size A lesser volume or the same volume can be selected for the x y z extents Cell dimensions for x y and z can each be a different length but a constant set of cell dimensions must apply throughout the voxel model The default discretisation scheme suggested 20 x 20 x 20 divisions in each direction This results in the cell dimensions x 500m y 500m and z 100m 5 9 10 11 Now we can decide which geophysical observational grid data type to use Fields to Compute In this case for a joint inversion tick both Gz and TMI Return the highlight to the first data type Gz Click on the Browse and navigate to TutorialE2 Data Observed_Gravimetry_BuriedGranite ers gt Open Highlight to the second data type TMI Click on the Browse and navigate to
73. ion identified or by 3D data e Sections names amp any associated geo located images e Drillholes ID and geology intercepts e 8D geology if a 3D model or 3D grid is built visualised in the 3D Viewer e Meshes and grids if one or more is loaded in the 3D Viewer Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 17 Contents Help Top q Back gt Explore Ry cs Ed Ry ci EJ 2 MNT EJ Fr Section 400 Ed j New _Project T Formations Cc series a F Sections g i ie Drillholes rq H Series_3 Fa a Series 2 af c jia m EJ 7 am pa Series_1 7 o E z a Grids and Meshes i as P The image above shows contact interface data for the tops of 2 formations in our model this is an example of data type 2D They were added to the section using the pencil create tool from the 2D Toolbar 7 View the stratigraphic pile for the BuriedGranite 3D model From the main menu choose Geology gt Stratigraphic Pile Visualise Every aspect of the way the stratigraphic pile is set up will have an impact on the way that the interpolators will run and how the resulting geology shapes and lines will be built We call this rule based modelling It is intuitive for geologists and geophysicists and unique to 3D GeoModeller E
74. ity eos EE lt tdDevSusceptibility Lad MostProbable 2 BE MostProbableThresholded y Prob_AboveTopo ge Prob_Cover ge Prob_Host_rock Pa Prob_Granite The following table explains each property field of the 3D mesh grid We will only be analysng and or visualizing some of them in this tutorial Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 73 Contents Help Top 4 Back gt File s Description Change Count The number of times this particular voxel has had a change Entropy Relates the volatility or change degree of the particular voxel throughout inversion in respect of geometry changes Represented as a number from 0 low volatility to 1 high volatility Mean density The mean density as derived from the accumulated accepted inversion proposals models which occurred between burn in and the last iterations Standard Deviation Density Directly related to the above mean as derived through the PDF Mean Susceptibility The mean magnetic susceptibility as derived from the accumulated accepted inversion proposals models which occurred between burn in and the last iterations Standard Deviation Directly related to the above mean as derived Susceptibility through the PDF Most Probable For each voxel location this field records the lithology identity that the
75. k gt GeoModeller User Manual Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 46 lt 4 Back gt 3 Choose Axis Aligned XZ Choose Slice XY 4 Use the slider bar on Axis Aligned XZ to reveal the interior cells of the slice fae 2D Viewer Clipping Axis Aligned y 2000 0 1000 0 W XZ U 00 o 000 0 F E YZ j 0 0 5000 0 Slice Wx Flxz F Yz Contents Help Top 3D Viewer Clipping Axis Aligned y 2000 0 5 0 0 10000 0 iw XZ o i 10000 0 Reverse 2 000 0 0 3 900 F Panan ee subi 0 10000 0 Reverse Fix xz 4 close 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 47 Contents Help Top 4 Back gt E2 Stage 3 2D seismic calculation The first job is to set a seismic velocity for your geological formations 1 Dothis in the main menu by choosing Geophysics gt Define physical properties 2 Choose the Seismic tab Create velocity contrasts between the 3 geology units in our model by entering the values for a log normal distribution in the table below Enter by clicking on each number field we ae ao fn C E ba icine Formation Velocity m s E Cover Log normal 1200 20 100 E Host_rock Log normal 1800 20 100 Log normal 1500 20 100 General Parameters Velocity Ref
76. l case study E Forward and inverse modelling of potential field data 63 Contents Help Top 4 Back gt Execution of Environment Settings Just prior to running an inversion you must make a decision about where to run the job and how many CPU resources to request to do it The default is to use your local machine interactively You may have more than one CPU and an operating system is designed to allow you to continue to work interactively while number crunching continues in separate process es 1 Accept the default to run Interactively 2 Accept the default maximum number of cores to run on your computer this prioritises the inversion process If you need other processes to current concurrently choose a lesser number of cores to dedicate to the inversion task 3 Choose Finish r 3 Create Inversion Case mym Execution Environment Settings Edit Setasdefaults Number of Cores 4 Kea z mh E5 Stage 5 Monitoring the misfit and computing post burn in summary statistics Immediately when running interactively a progress bar in the form of a current misfit vs iterations graph pops up As the inversion gets underway a pop up graph shows us a high initial misfit which rapid settles lower and then constant When the 500 000 iterations are complete you will be asked if you wish to compute Summary Voxets also known as Super Summary Statistics SSS which collates
77. lour Refresh B gt Image Manager Save Image Section Data Hide Modelled Geology Polygons in 3D Viewer Show Modelled Geology Lines in 3D Viewer Erase All Model Geology h SO e 400 Properties 2000 15 Save your project From the main menu choose Project gt Save NOTE Managing the Geological Editor is not the main objective of Tutorial E and a brief overview has only been given here for this reason For further instruction on the Geological Editor functions of 3D GeoModeller go to Tutorial Case Study A in the Main Menu gt Help gt Manual amp Tutorial PDF Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 24 Contents Help Top 4 Back gt Tutorial E2 Potential field forward calculation Parent topic This tutorial takes the user through a typical sequence of tasks for forward modelling ay case of potential field data directly from 3D geology models study Forward and In this tutorial inverse modelling of e EK2 Steps Overview potential field data e E2 Stage 1 Enter physical properties E2 Stage 2 Forward calculation E2 Stage 3 2D Seismic calculation E2 Steps overview 1 2 The first task whether we are going to carry out forward or inverse modelling will be to associate physical property distributions with each for
78. lume Ratio Test LocalAbundance hi E Allow Commonality Volume Test rane Geophysical Criteria Allow Geophysical Misfit Tests Advanced Tuning Options speed of initial solver For this tutorial 1 Change the number of Iterations to 500 000 500 000 iterations is enough in this exercise to get convergence to a uniform misfit between the model geophysics responses and the observed geophysics grids The further iterations past the initial convergence after Burn in allow for an exploration of all the equally probable models that follow Millions of equally probable models each with a small variation in a property or geology boundary can explain the observed data sets 2 Tick on Allow Formation Geometry Tests 3 Tick on Allow Commonality Test Weighting option to the right leave default as none 4 Tick on Allow Volume Ratio Test Weighting option to the right change to Local Abundance 5 Leave default on Allow Geophysical Misfit Tests 6 Choose Next Weighting options are explained in the Reference Manual forward modelling and inversion with 3D GeoModeller 2012 The advanced options are available for testing and for influencing the speed of the solver in the initial convergence stage For this tutorial leave Advanced Tuning Options unadjusted Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutoria
79. main GeoModeller menu choose Project gt Open OR From the Project toolbar choose Open amp OR Press CTRL O 3 Browse to and open the pre created 3D GeoModeller project GeoModeller tutorial CaseStudyE TutorialE6 E6Beginning_ Project E6Beginning_Project xml where GeoModeller is the location of your 3D GeoModeller installation for example C Geomodeller Geomodeller 4 From the main menu choose Geophysics gt Define physical properties Series Mean Standard Statistical Percentage Density Deviation Law of Lpopuuen Series3 Granite LogNormal amp NEWeranite i LogNormal 5 Ensure the above values are entered for densities We will only be creating a gravity full tensor grid so only densities need to be checked Note that NEWeranite is a geology object created for the purpose of tutorial E5 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top E6 Stage 2 Forward calculation of a gravity full tensor grid Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 89 lt 4 Back gt Now we will set up and compute a full tensor gravity field Free Air directly from the 3D geology model 1 From the main menu choose Geophysics gt 3D Geophysics gt Forward wizard 3D GeoModeller displays the forward calculation area of 3D Geophysics tool Choose Gravity Tensor in the Fields to compute ar
80. mation We then carry out a forward model calculation to see whether the combination of the geological model and the choice of physical properties produces a response that broadly corresponds with the measured observations You need to perform the following operations on the geophysical observations 3 10 3D GeoModeller expects the observations to form a regular grid and to be the response observed on a horizontal plane or a draped surface Especially with the spatial forward modelling algorithm we have added provision to reduce any aliasing of the response due to topography effects If this is insufficent you may wish to reduce aliasing effects by upward continuing the data For vertical gravity and TMI data types a terrain clearance of half to one vertical cell height respectively would be sufficient Make adjustments to the geophysical observations to remove the response of material that will not be considered during the inversion phase This process is generally called regional removal 3D GeoModeller inversion obtains formation and geological boundary information from the current project Enter the parameters that define the distributions of properties for each formation into a table in 3D GeoModeller Supply a grid containing processed geophysical data for each data type Run the forward modelling calculation either for magnetism gravimetry or both When 3D GeoModeller has finished you can view the observed geophy
81. misation The aim is to get your 3D geology model not only to be consistent with all the known geology observations but also to explain main features of regional geophysical datasets such as a Free Air gravity or a Total Magnetic Intensity grid To achieve this you need to specify rock properties If you are confident of your geology model and have an observed geophysical grid of observations then you can use property optimization to deduce bulk average rock properties needed to explain the observations How it works Spatial discretisation We provide a technology algorithm that can give you a bounded least squares optimi zation of the property estimates using your model with relative coarse cells in the XY and finer ones in the Z direction Response kernel A response kernel for each lithology is needed for property optimisation These are calculated automatically if you choose the Run Property Optimisation option in the forward wizard Once the response kernels have been calculated property optimi sation 1s run and a report file is displayed with the optimised property values Also to be effective it is best if there are at least 8 lithology units Bounds Additional to the standard Property Law such as Normal Distribution with a mean value and a Standard Deviation you also must provide two extra fields a LOWER and an UPPER bounds The purpose of these is to constrain the resulting estimates to be within bounds which are reaso
82. n between 0 and 100 This is usually then displayed in a black grey white colour scale 6 From the Explore tree select the MostProbableThresholded property field _ Explore b New _ Project cH fa Formations 2 i Po Dykes nE Ad Faults A Sections MA Drilholes por g 30 Geology i Ws Grids and Meshes mi z Observed_Gravimetry_BuriedGranite e 3 SummaryStats_400000 500000 Threshold _90_super 2 12 ChangeCount Hl Entropy BSS MeanDensity EN stdDewDensity MeanSusceptibility bee StdDev Susceptibility EE MostProbable EE MostProbableThresholded so BMG Prob_AboveTopo be BMS Prob _Cover ae Prob_Host_rock i EN prob_Granite 7 Select MostProbableThresholded gt right click gt Properties bottom of list 8 Chanee Alias to Lithology type aL Manage MeshGrid Field Properties Name MostProbableThresholded Type Real Units Lithology Alias i Description Elements 8000 Memory usage 62 5 Kb 9 OK 10 In Explore gt MostProbableThresholded right click gt Edit Colours amp Clips Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 75 Contents Help Top 4 Back gt 11 Select a Visibility Clip from 0 to 1 5 to isolate granite pink and the zero field white which represents cells which resided below the threshold of 9
83. nable If you find the estimated values are all at one end of the bounds or the other chances are that you do not have a good geology model or an understanding of typical rock properties to go further without doing more inves tigations Spike rejection To make sure you use representative values of observed data a maxAbsoluteObserved field is available to ignore outliers You may have a genuine very high observed reading in your data that would distort the general background properties for a unit so this allows you to limit the influence of an outlier observation Solver method The solver uses a weighted least squares approach over the whole 3D assembly of cells and properties to best fit the observed data and the response from each individual unit summed by its response kernels Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 50 Contents Help Top 4 Back gt Running a property optimization exercise for this case study Buried Granite THIS TUTORIAL IS UNDER DEVELOPMENT PLEASE CONTACT INTREPID GEOPGHYSICS FOR FURTHER INFORMATION AND TO ASK THE RELEASE DATE FOR TUTORIAL E3 Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field
84. nd changing the properties of a unit in any one iteration Property Only Case Probability of property change only 100 When you feel very confident about your geology model and you already may have got bulk physical properties that do a good job of reproducing the observed geophysical response from that model more subtle features may emerge in pockets if you allow a 100 probability of property change only run The reason for this is that a non deterministic exploration of probability space will show you the probability of coherent property anomalies at depth within various units You may also restrict which units to explore this way by setting the Standard Deviation to zero for those units you want to exclude from the study This way just one or two units are in play This approach which locks down the geology could be thought of as a sophisticated Property Optimisation Geology Only Case Probability of property change only 0 The other extreme is similar to the algorithms used in more traditional gravity mag inversions for solving depth to basement You hold all the properties constant and force geology boundary changes as the only way to reduce the misfit in the study Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 59 Contents Help Top 4 Back gt Conten
85. odule toa mesh or block model form We assume the lithology at all points within each mesh element to be the same as the lithology we calculated based on the continuous geological model at the centre of the cell 3D GeoModeller announces when it has started the re sampling operations required to discretise the model The time required for these calculations depends on the number of elements in the mesh The time may be only a few seconds for a mesh with a few tens of thousands of elements for example 40 x 40 x 20 cells or many minutes for a mesh with several million elements for example 200 x 200 x 100 cells 3D GeoModeller initialises the appropriate physical property model density for gravity calculations and magnetisation for magnetic calculations using the mean value for each formation 3D GeoModeller announces when the forward calculations are ready to start The forward calculation for a typical mesh for example 100 x 100 x 50 elements should take no more than a few minutes 3D GeoModeller displays the results in the 3D Gravity Forward modelling window Lateral padding of a model Information Contents Help Top The illustration below shows a plan view of padded litho model arrangement used in the forward model response calculation Before undertaking forward model calculation using either spatial or FFT methods we pad the model volume by surrounding it with 8 copies of the model 2013 BRGM amp Desmon
86. ogy gt and select Wireframe to change the displayed 3D volumes to wireframes Inthe Project Explorer right click 3D Geology gt and select Shading to toggle the 3D display of geology back to shaded 10 Change individual geology units of the model in the same ways as above In the Project Explorer click the plus symbol to expand the list within 3D Geology Again expand the plus symbols for each series in the model 11 For the series3 unit Right click on Volume Cover to gt Hide from the 3D viewer 12 For the series2 unit Right click on Volume Host rock to gt Wireframe 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 23 Contents Help Top 4 Back gt g 3D View oo 1 Pata 500 wn 120 ons et LL Wan Bo eS ta ie oo 2 000 To Show modelled geology polygons or lines in the 3D Viewer 13 Select a 2D section for example C3 ensure a green tick appears top left 14 Use the shortcut menu right click the background of the 2D viewer and choose Show Modelled Geology Polygons in 3D Viewer YR EJ ct mnt EJ 4 section 400 Ed E 3D View ia w Hide Shading Appearance B 907 Plot the Model on the Current Section Vertical Exaggeration E Reset View Display Parameters Presentation D Background Co
87. ogy Onentation Data Geological Formations and Faults NEWoranite Observation ID c2 Provenance Unspecified Coordinates x 8237 5381 Direction Dip Direction 210 439 Polarity Normal Reverse Overturn Automatically Re edit Automatically Update Coordinates Help Undo yf Create Guidance is also required for the shape of the NEWegranite surface as described on Section C3 1 Repeat Steps 1 to 7 above for Section C3 2 New orientation data in the approximate locations as show below are recommended Compute the 3D geology Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 86 Contents Help Top 4 Back gt Compute the 3D geology model for the project that we have loaded to be constrained by the geological data and pile we have reviewed 1 From the Model toolbar choose Compute or press ctrl M In the Compute the Model dialog box e Series to interpolate Select ONLY Series 2 and NEWegranite Series e Series 3 is Cover This will automatically generate between series 2 and the topographic surface We DO NOT wish to include Series1l original granite e Faults to interpolate Select All e Sections to take into account Select All e Faults only Clear therefore DO compute faults 2 Choose OK fag Comput
88. olution Build 4 Formations W Faults Type GP Volume i Column EF Surface 7 Draw Shapes after Building Resolution F Render Quality Low Medium lattes mi madison Ecce Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 22 Contents Help Top Contents Help Top lt 4 Back gt In the Build 3D Formation and Fault Shapes dialog box Check Build Formations Check Build Faults Select Type Volume Check Draw Shapes after building Adjust the Resolution Render quality to Medium Choose OK 20 View coat D I y Z ii k anny aes is i OLU a ern all will Use Project Explore to Manage the 3D Viewer View the model in 3D 3D GeoModeller computes the 3D shapes of the geology model as solid volumes defined by triangle mesh surfaces which it displays in the 3D Viewer Use the Project Explorer typically on the left side of your work space to manage the display of modelled objects in the 3D Viewer 9 Experiemt with change whole model appearances Inthe Project Explorer right click 3D Geology gt and select Hide to hide the entire modelled geology Inthe Project Explorer right click 3D Geology gt and select Show to show again the entire modelled geology Inthe Project Explorer right click 3D Geol
89. on team s task now is to build a starting 3D geology model for the focus area and adopt some appropriate physical properties for the geological formations based on locally accumulated data sets for density and magnetic susceptibility and generic published tables As a starting model your exploration team propose an elongated granite dome within a homogenous host formation two units in total Initially the team agrees the slab may have dimensions of 450m length x 150m width x 200 metres height and is buried 200 metres below the surface Introduction to litho constrained inversion of gravity and magnetics Parent topic Introduction to Case Study E Contents Help Top Because of the non uniqueness associated with both geological and potential field observations we cannot tell whether the 3D geological map in the current project and the estimates of the physical properties are a good approximation of the truth or not The most that we can say is that this combination of geometry from the 3D map and properties from the supplied distributions 1s one of many solutions that would be consistent with all of the observations However if this combination of inputs produces a response that is significantly different to the geophysical observations we can conclude that combination is extremely unlikely to be present The inversion method implemented in 3D GeoModeller begins with linked lithology and property models which we assume
90. on with 3D GeoModeller 3D maps supported 3D maps supported by the geological by the magnetic observations observations 3D maps supported by the gravity 3D map produced observations from the mapping module using the geological Most probable 3D observations map produced from the inversion module using the geological and geophysical observations The geological scenario and starting 3D litho model Parent topic Your exploration team has identified what they hope to be a swarm of volcanogenic Introduction to massive sulphide deposits from the initial airborne gravity survey More detailed Case Study E l surveys of gravity and magnetism have been flown in follow up exploration revealing many anomalies in both the gravity and magnetic signature Following image processing enhancements of the potential field data sets Kuler methods automatic depth determination and multi scale edge detection analysis have been carried out and your exploration geophysicists have singled out the location of one of the largest anomalies They recommend the team focus on this anomaly for higher resolution geological interpretation prior to planned drilling Their initial assessment of this anomaly is that it appears to reflect the presence of a rough granite body elongated in a north south orientation and buried at least 200 m below ground surface The setting may be part of a well developed rift with faulting on the edges of
91. ontents Help Top 4 Back gt two voxet properties Lithology and Density Explore l i s J ES New Project Browse the project s objects al P Formations A po Dykes 1 iTi Faults P E Sections i Drillholes pe g 30 Geology i Grids and meshes 2 Observed_Gravimetry_1 gt EA Observed_Gravimetry_1 4 calculated_Gravimetry_1 cw BN calculated_Gravimetry_1 3 BE inital Z EN ithology Bl Density 5 Choose the Lithology field then right click 6 Check the Field Visualization Manager and then View grid in 3D ia gt iso values EI a 3D Points 3D Volume 7 View gridin 3O View isosurfaces in 3D Sections view Sections View on section View on Section in 3D All The voxet appears in the wireframe of the 3D viewer If the interpolated 3D geology model is also in the same space go to Explore gt 3D Geology gt hide 7 Now in Explore check initial gt Litholgy gt Histogram The 3 units are shown as seen below left What you see left is the volumetric proportions of each geology unit in the lithology voxet model as created as Casel during forward gravity modelling 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 45 Contents Help Top 4 Back gt 1 To see the
92. ord of the misfit evolution Misfit degree for gravity and magnetics as a function of iteration number effects _Gravimetry_l ers 2D grid of the computed gravity response from the initial iteration of the inversion final_Gravimetry_1l ers 2D grid of the computed gravity response from the final iteration of the inversion effects Magnetism_2 ers 2D grid of the computed magnetic response from the initial iteration of the inversion final_Magnetism_2 ers 2D grid of the computed magnetic response from the final iteration of the inversion initial vo Initial voxet 8D grid 4 attributes initial lithologies fixed cells initial densities initial susceptibilities final vo Voxet 8D grid for the state of the model at the final iteration 4 attributes final lithologies fixed cells final densities final susceptibilities reference vo The geophysical response kernel voxet model 8D erid discretised at the same cell size as the voxet models above Summarystats_400000_50000 A summary statistics mesh grid voxet for re 0 Threshold_90_super vo compiled results and settings captured between burn in 400 000 amp end of iterations 500 000 For further details of this key file see E5 Stages 8 amp 9 Casel_Run1 txt Log of change to the geology model voxet for reconstructing the state of the inversion during the evolution For headings and further information see the Inversion Manual Contents Help Top 2
93. ost_rock Discussion Other features of support for 2D seismic surveys include an importer of seismic navigation files that automatically creates GeoModeller sections We enable rapid creation of a 3D geology model in an off shore continental margin setting by e using the 2D seismic picks that are being interpreted in a Time based context e bringing these plus the lines into a 3D Depth based context e using the potential field interpolator of GeoModeller to rapidly create 3D bodies that fill the whole project volume The gravitational response of a body is easily computed so that any misfit with observed marine gravity data becomes obvious This then leads to queries for the seismic picking team to mull over and perhaps re think some of the horizon returns To do something similar with either Gravity or Magnetic profiles is quite easy Any geophysical database that is line based and has field observations can be used to create sections down each line and have its profile tested for a fit with the underlying 3D geology model Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd lt 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 49 Contents Help Top 4 Back gt Tutorial E3 Potential field rock property optimization In this section e K38 How it works Information e E38 Run and monitor the Property Opti
94. perty model You can carry these calculations out relatively quickly and accurately to predict the gravity and magnetic response given a 3D model of density and magnetisation respectively Property optimization is a term used to describe a simple way to improve the overall fit of your geology model to any observed geophysics grids you may have Often your rock property knowledge especially of deeper unit s is very poor With this technique you can easily come up with average properties that make a best fit overall for each unit With this it is much easier to then judge if your geology model is giving a reasonable first fit to the geophysics Inverse modelling or inversion is the reverse operation to forward modelling attempting to derive a physical property model given a set of observations With potential field data this is a much more challenging process than forward modelling because there is more than one possible solution To circumvent this characteristic termed non uniqueness you can define some preferred characteristics for the solution The inversion program can then find one or more solutions that not only reproduce the observations but satisfy your preferences In this instance these preferences or constraints are in the form of the 3D geological map and the physical property distributions that you define for each geological formation in the map References The following references contain additional background information
95. property change law So even if you want to fix the geology geometry of a model and just doa property change only inversion the properties generated are still confined to what is allowed within each law re Create Inversion Case Geophysical Settings Lithology Physical Properties Granite E Cover Gravity Density Host_rock Magnetic S Susceptibility Remanence Common v Indude border effect Gravity Magnetic Susceptibility initialisation FromLawRandom X Remanence initialisation FromLawMean Ee a Total magnetic field 56600 nT 7 6 degrees 62 degrees Normal 2 8 0 1 100 reese Log normal 0 004 0 0002 100 Normal 0 0 100 0 0 L__ lt Back 1 For GRAVITY set FromLawRandom 2 For MAGNETIC set FroomLawRandom settings are appropriate for both In the lower field toggle between the Gravity and Magnetic tabs to check the field Check reference density 2 67 g cm Above topo density 2 67 g em Total Magnetic Field 56 600 nT Declination 7 6 degrees Inclination 62 degrees 4 choose Next E5 Stage 3 Enter geology body constraints and laws for change The Create Inversion Case Geological Settings page is for setting controls on the style of geology constraints during inversion Left Hand side Shared settings deal with controlling the generation of proposals for change in your model Create Inversion Case Geological Setting
96. r Log normal 2e 005 12 006 100 Mormal o 0 100 0 0 Hestlroeck Wormal o 0 100 Mormal o 0 100 0 0 SERIE ormaK0 0 100 General Parameters Magnetzatoan IGRF Calculator Total Magnetic Field nT 56600 Declination degrees 7 6 Incination degrees 52 0 wal OK Eg Clase Note The magnitude of the induced magnetisation is the product of induced susceptibility and the magnitude of the ambient field Inclination is positive below the horizontal and declination is positive east of true north OK to close and save the new values Further Information Settings Number of modes Statistical law or distribution type Parameters to define the distribution Proportions Gif more than 1 mode For each formation and property you can select the number of modes the statistical law for each mode if multi modal then assign two parameters Mean value and Standard deviation These define the distribution for each mode if multi modal For multi modal options you also specify the proportions for each mode For a Normal distribution the Mean value and Standard deviation have a meaning that 1s well understood For a LogNormal distribution the Mean value is the natural logarithm of the mean and the Standard deviation is the standard deviation of the natural logarithm transformed values For an Equal distribution the Mean value is the central value and the
97. raphy allow sufficient project space at the bottom of the model to cover the entire range of modelled geology and geophysical data that you are interested in E1 Stage 3 Re compute and review the 2D and 3D views of the geology model Contents Help Top E1 Stage 3 Steps Compute the 3D geology Compute the 3D geology model for the project that we have loaded to be constrained by the geological data and pile we have reviewed 1 From the Model toolbar choose Compute or press ctrl M In the Compute the Model dialog box e Series to interpolate Select All e Faults to interpolate Select All e Sections to take into account Select All e Faults only Clear therefore DO compute faults e Choose OK 3D GeoModeller computes the model Nothing to see yet The model is a mathematical model a set of interpolator equations that are computed from the geology contacts and orientation data There is an interpolator equation for each series in the stratigraphic pile and also an equation for each fault Eg Compute the Model Interpolate Geology and Structural Data Geology and Structural Data Faults Only Series to Interpolate Faults to Interpolate Select All Parameters Hint Select All Deselect All Select All Global Parameters Model Limits Data xMin Oo XMax 10000 m Use Points Simplification Radius 10 m Min oO Max 10000 m a Use Points ZMin 2000 ZMax o m Use Points
98. roject TutorialE1 E1Beginning_Project xml where GeoModeller is the location of your 3D GeoModeller installation for example C Geomodeller Geomodeller or home geomodeller Geomodeller for a LINUX install 4 View the already computed 3D geology model as rendered in the 2D viewers Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 16 Contents Help Top 4 Back gt Main Menu and Main Toolbars pectin Peet Ce TBP Piac FE tpt betien ectogy Mizdel Gegi btepelshoe beet E Wire Wits r a bigip E e BEES uF ayr OGF YO warr Go TO eB amp fF Bet AA F BEA T ie Explor mel wa My ce Ed iy ce EJ eo ee EJ FF serions Ea MF 3b ve gt w E r Fot J a Ead We 3 A sEm aa Bisons Se Howe be EE Ej E z Fj i em ce wl kas aia MHT T au Ls r Trein z en ppn E Bites La B sectore fi Mer Pi M Aa 6 FF Secnent0d i Ceri cs a Lae ares ted aca 2D Toolbar 2O Viewers and 30D Viewer 30 Toolbar 5 Examine the main elements of the GeoModeller workspace labelled above gt 2D Viewer contains 2D sections This tutorial E1 project contains several sections C3 and C2 which are already rendered when the project opens e We use 2D sections for storing and or digitising geological data input and for rendering 2D plot
99. rs P Observed calculated_GravityTensors_1 Misfit 8750 0 aaa a750 0 7250 0 7250 0 7250 0 57500 5500 51500 E 42500 42500 E 4250 0 gt gt 77500 7750 0 ana 12500 125000 125000 2500 2500 200 500 1250 0 27500 42500 57500 72500 8500 2500 1250 0 27500 4250 0 5500 72900 87500 2500 1250 0 2750 0 4250 0 57500 72500 87500 X m X m X m SSJc em mm RSs aa y D 0 1 w a n 4 2 m 2 a v a a y a n Pa y Regional Trend 0 lt v lt 0 Computed Regional Trend 36 274 lt v lt 89 774 Misfit Regional Trend 89 774 lt v lt 36 274 Regional Trend Computed Regional Trend Misfit Regional Trend asno aso ano 7o 72500 7250 0 7500 m 5500 ana E a0 E ao 40 gt gt 77500 75010 7500 12500 125000 125000 I 7 M M a 2510 M C 2500 12500 2750 0 42500 57500 72500 N0 2500 12500 2750 0 42500 57500 72500 87500 2500 12500 27500 42500 57500 72500 VNO X m X m X m RSS i C lt i sS Dao om nmw asm g D 1a asasan n wow az Regional Settings Degree 0 Constant Regional 0 Apply Solve Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 93 Contents Help Top 4 Back gt When the forward model calculations have been completed 3D GeoModeller displays several full tensor grid images by a Cube Root Det
100. rt to be made capturing the results with equal probability of being good answers There can be millions of equally plausible answers 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd Back GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 12 Contents Help Top 4 Back gt Detailed inversion flowchart The flowchart below explains 3D GeoModeller inversion workflow in greater detail CURRENT MODEL Form next proposal a Decide whether changing property only or lthology amp property b Ensure the voxel can be changed eg Nota fixed cell c Make the change nb Lithology change will only be to a frontier cell Geology Tests Examples i Are set Commonality tests satisfied Ts the proposed litho model acceptable Passing all geology tests agains the reference vowet li Are set Volume Ratio Wor Shape geology model Ratio tests satisfied MO TES Randomly and independently resample each property for the voxel Select next geophysical dataset using order of supplied grids Forward model the relevant property field and match polynomial trends between calculated and observed grids if appropriate Calculate the likelitood for the proposal Lp _ 5 NO YES Proposed model is more likely than the current model Lp Le Obtain random marker from egui probable distri
101. s Shared Settings Lithology Specific Settings Proposal Lithology 7 Allow Property Change on Fixed Cell s E Cover 4 Allow Local Property Difference Check Not Re Host_rock Probability of Property Change Only 505 Miscellaneous V Fix Individual Cells Containing V Surface Intersections Points from CSV File Browse Any Observed Contacts Selected Observed Contacts Unspecified Observed Inferred Interpreted ModelConstructo Select all De select all Properties Fix Lithology Frontier Constraints Commonality Weibull 0 2 1 0 100 Shape Ratio LogNormal 0 1 0 1 100 Volume Ratio LogNormal 0 25 0 05 100 Commonality Volume Normal 0 0 1 0 100 Always above these Lithologies Cover Granite Ea XY AANI Stratigraphic Order Reset Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 58 Contents Help Top 4 Back gt 1 Leave the default ticked on Allow Property Change on Fixed Cell s Usually the fact that a cell has fixed geology should not preclude its properties from changing within the constraints of its property law 2 Leave the default ticked on Allow Local Property Difference Check This option keeps local variations of properties in the immediate neighbourhood to a minim
102. s appears next to the Grids and Meshes expand this directory twice to reveal 4 different property fields of this attributed 3D grid Voxet 8D grid for the state of the model at the final iteration 4 attributes fixed cells litholgies densities susceptibilities Select Susceptibility Right click gt Histogram Use the bottom right hand corner tab to Open each lithology in turn Host_rock Cover and Granite ALL is shown in the first view 7 Select Host_rock as shown below Histogram of Susceptibility Statistics Histogram of Susceptibility DGS Sigma 0 000149 Fri Susceptibility SUONBNASO jo Jaguwny 0001F 0 0018 0 0018 o 0020 0 0021 0 0022 0 0023 0 0024 0 0025 0 0026 Susceptibility 1 Toggle through each lithology in turn noting the Mean Magnetic Susceptibility and standard deviation for each and here is a summary of the distributions that were recorded in the final iteration of the inversion Note The following table gives an indication of the expected values Lithology Mean Susceptibility Standard deviation 0 00002 0 000001 0 004014 0 000233 0 002028 0 000148 Note that similar statistics can be analysed in regard to densities susceptibilties derived from the accumulated accepted inversion proposals which occurred between burn in and the end of iterations instead use Summarystats_400000_500000_Threshold_90_super vo rather than those shown here which relate to the last iteration only final
103. s designed to improve your knowledge about the geology geometry and rock properties of your project The Forward modelling and inversion with 3D GeoModeller 2012 Reference Manual contains more detailed references and explanations of the methods used in this section In this tutorial e E5 Introduction gt E5 Steps Overview E5 Stage 1 Create a new case E5 Stage 2 Check rock properties distributions E5 Stage 3 Enter geology body constraints and laws for change E5 Stage 4 Enter run control parameters E5 Stage 5 Monitoring the misfit and computing post burn in summary statistics E5 Stage 6 View the final 2D grids for magnetics and gravity quality check e E5 Stage 7 Statistical results analysis and visualization E5 Stage 8 Analyse 2D amp 3D composite views of resulting geology geometry E5 Stage 9 Create 3D points of inversion driven geology Export Shells cvs E5 Introduction To set up and run a litho constrained inversion You only need to access the Geophysics menu The Geophysics menu operations directly access the geological information in the current project including the physical properties tables so there is only a modest amount of additional information to supply in the Inversion wizard Some of the pages of the Inversion wizard are similar to the Forward Modelling wizard such as the need to set properties choose grids and set the run environment The main differences
104. s in 2D Manage the colour table and data range clipping to enhance the details Property Optimisation Tutorial E3 5 If the results of the forward calculation are broadly similar with the measured observations then you can skip property optimisation However if the predicted response of the starting model bears little resemblance to the measured geophysics this violates a fundamental assumption of the inversion methodology and the end results will be meaningless should you not optimise the properties in some way one method is demonstrated here An assessment of new mean and standard deviations of rock properties per lithology that are returned Adaptation of your improved understanding of rock properties prior to inversion Prior only Inversion Tutorial E4 6 Perform prior only inversion to see what probability space is implied by the geological constraints geology tests that you are going to set In this case there is no concern here with the reduction of the calculated misfit between predicted and observed geophysics no likelihood of the new proposal is calculated at each iteration nor compared with the reference geophysics grids Joint magnetic gravity inversion with stochastics Tutorial E5 7 You will supply suitable parameters and carry out the joint litho constrained inversion calculations The inversion program searches for models that e Satisfactorily reproduce the measured geophysic
105. s of our 3D model e You can also open section MNT the Topographic or Map section This is a special type of 2D section in that it retains the information of the draped grid of the digitial elevation model DEM if one has been used to build the project If not then this section will be a horizontal plane of a specified height as used in this case study sea level Check this by moving the mouse over the MNT section and observing the x y z mouse location in the lower left corner of the workspace z is constantly 1 0m in this project e Note the topography section MNT here defines the rock air interface of your model Generally we recommend using a DEM to assign the correct topographic shape as this allows more accurate mapping of geology on surface 8D Viewer contains a 3D view of your project or a wireframe bounding box if the model is not yet visualised At the stage opened see above a Visualise 3D Formations and Faults has not yet been done we will do this later 6 Also note the Project Explorer located to the right of the 2D Toolbar e Project Explorer this has a tree structure containing details about the many objects making up your 3D geology model e Formations in the stratigraphic pile and what data type the contraints exist in by 2D data on individual sections or by 3D data or by drill holes e Faults in the project and what data type the contraints exist in by 2D data with the sect
106. se study E Forward and inverse modelling of potential field data 8 Contents Help Top 4 Back gt Increasing use of geological prior information with gravity and magnetic data Sy Image processing enhancement e g RTP 1VD Horizontal gradient maxima worms Sem automated depih to s ource methods Default UBC inversions UBC inversions using a reference model Qualitative inte pretation Modelling with polyhedral bodies Modelling 20 sections 3D litho model exploration e 9 Geoliadella VPmqgi The need for a close initial 3D geology model Parent topic Introduction to Case Study E Contents Help Top Most successful use of the fully constrained lithological inversion method is achieved by first creating a starting or reference geology model that is consistent with all of the geological observations and also closely honours the observed geophysics signals for most of the study area This is necessary because the Monte Carlo techniques adopt very detailed processes of changing individual properties or geometries and a close starting model will ensure you minimize the time needed to explore probability space and maximize your chance of converging quickly to an acceptable mis fit allowing time to continue on gathering good statistical results Below is a histogram illustration of a non viable reference model prior to any inversion The left hand population from a forward model of the gravity response is a complet
107. served Grid 4 Specify an Observed Grid From External Resource D TEMP_TUT_E CaseStudyE_HG TutorialE2 Data Observed_Ground_Gravity_BuriedGranite ers Band 1 Calculation Surface Constant elevation Drape gt Terrain dearance Drape gt Load from dataset Supported reference grid formats Information Contents Help Top The default grid format is ERMapper ers format Beneath the hood we use the generic Intrepid GridIO drivers that are capable of auto detecting a range of industry standard geophysical grids Some formats support multi band grids ie there are multiple data fields within the same grid An example of a 4 band geophysics grid would be radiometrics data with bands 1 2 3 for K Th U and the fourth band for the Total Count Choose the band that you want to use as an observed grid Tensor grids are stored in 6 bands by Intrepid The semi format is a very simple ASCII XY value format that can be used if you are having trouble obtaining a standard grid With the Kriging capability within Geomodeller you can also import gravity point data or an airborne survey magnetic channel and grid the observations prior to this importing step see the reference manual The extent of the grid of forward calculations is the intersection of the extent of the supplied grid and the plan view extent of the current project The spacing between observations in the forward model output is identical to
108. served_Gravimetry_BuriedGrani Observed_Gravimetry_BuriedGr G 2 effects_Gravimetry_1 effects_Gravimetry_1 H effects_Magnetism_2 4 final_Gravimetry_1 E 4 final_Magnetism_2 3 Color Table final_Gravimetry_1 RA E Save PNG EJ close 4 m p Import as many 2D grids as you want to compare by repeating steps 2 3 and 4 above When loaded they stay in your Explore tree Geo register the grids and display the colour table by repeating Steps 5 to 8 above Use Grids and Meshes right click gt Hide all Views to refresh your MNT Viewer before viewing the next grid 9 For Example Browse to CaseStudyE TutorialE5 Data Observed_Gravimetry_BuriedGranite ers MW Drillhole 30 Geology a 2 Observed_Gravimetry_BuriedGrani ma Observed_Gravimetry_BuriedGr AMM effects_Gravimetry_1 4 final_Gravimetry_1 final_Gravimetry_1 Note the resolutions of the two grids are different A low resolution discretisation scheme was selected in the inversion settings top image for a fast outcome Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 69 Contents Help Top 4 Back gt E5 Stage 7 Statistical results analysis and visualization Topics covered in this Section E5 Stage 7 include e Load the final voxet and analys
109. sical grids the calculated grids and the misfits In the light of outcomes you can revise geology boundaries including adding new units and physical properties and repeat the forward modelling E2 Stage 1 Enter physical properties Contents Help Top K2 Physical properties Introduction EK2 Display physical properties in the geological unit dialog box Information K2 Set single mode mean density properties Steps K2 Set bi modal mean density properties Steps K2 Finalise density and magnetic susceptibility properties Steps 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 25 Contents Help Top 4 Back gt Physical Properties Introduction Parent topic E2 It is unrealistic given our knowledge of the real world to assign a single constant Stage 1 Enter physical property to each formation Every formation shows some degree of Soham heterogeneity We simulate this in the inversions by defining a distribution or spread of physical properties for each formation In a forward model the mean is adapted for the single run Display physical properties in the geological formation dialog box Information 1 From the main menu choose Geophysics gt Define physical properties 3D GeoModeller displays the Physical properties of geological formation dialog box Some default
110. spend some time checking the bulk properties This can be done using a new property optimization method You take your geology model give your formations a property distribution You also allow a lower bound and an upper bound for each property These bounds should be conceived and constrained by reasonableness If the results show that some properties required to explain the geophysics are consistently at one end of the bounds maybe your model is not as good as it needs to be During an inversion session 3D GeoModeller selects properties at random from the supplied distribution The algorithm is more likely to retain a selection that improves the fit between the observed and predicted geophysical response than one that increases the misfit between these two quantities Note that the distributions supplied for each formation are for samples having a 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 7 Contents Help Top 4 Back gt volume equal to the volume of the cells used in the models These cells typically have volumes that are many orders of magnitude greater than the volume of drill core or hand specimen samples for example a model cell 100 x 100 x 50 m in size has a volume 1 billion times larger than a sample 100 x 50 x 50 mm in size Much of the local heterogeneity seen in collections of dr
111. supplied grid coincide in plan view location with the centre of each mesh element 3 Choose Spatial as the computation method This is the default method which is now automatically thread safe That means it will use more than one CPU ona local machine The other option introduced here is a vertical sub cell resolution for topography modelling in order to reduce vertical aliasing due to honouring steps in the vertical resolution of your model It is recommended to use half the vertical cell size as a starting position and it really depends upon how rugged your topography 1s as to what to do here 4 Choose NEXT Review or edit your lithology properties NEXT review or edit your rock properties In this case we are doing a gravity Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 35 Contents Help Top Parent topic E2 1 Stage 2 Forward calculation Contents Help Top lt 4 Back gt simulation so we are just asked to review densities Leave the set values which are derived from the Physical Properties table as entered in the previous section Click on each coloured formation in the left hand side of the panel and the tool will show each property as you select the formation If you wish to change a value double click on the property law and the editor will appe
112. tProbable geology From the Explore tree select the MostProbable property field MostProbable gt right click gt Properties bottom of list Change Alias to Lithology type OK In Explore gt MostProbable right click gt Edit Colours amp Clips Select a Visibility Clip from 0 5 to 1 5 to isolate granite series 1 again select MostProbable right click gt Field Visualisation Manager CON OO OF FP WO DO tick the upper area View grid in 3D gt eal 4 Iso values ee 3D Grid ID View View Isosurfaces in 3D Sections View Sections View on Section View on Section in 30 Parameters Display Color Table Contouring Edit Colours and Clips of x vf Apply Fd close 9 Post inversion voxels deemed Granite in the MostProbable field of the summary statistics voxet are rendered in 3D Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 77 Contents Help Top 4 Back gt g 3D View m we 1500_ L Poon he 10 Having done a Model Compute gt Visualise 3D Formations amp Faults Tutorial E2 a wireframe view can be turned on in Explore g 3D View i 1H Kayo Fi 6000 W 4000 rc ae aii 500 a Ni ii 9 N 2000 a 11 3D Geology gt Hide clears the view 12 3D Geology gt Volume Granite gt
113. that of the voxet 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 34 Contents Help Top 4 Back gt used to calculate the forward response Enter Voxet Properties 1 Verify the number of cells in the X Y Z n 20 for all dimensions leave these defaults 2 Verify the vertical resolution of 100m where vertical sampling interval is given below Leave the default value 3 Create Forward Case Es Voxet Properties Set voxet resolution and processing options Voxet extents and resolution min 0 Xmax 10000 dX 500 nX 20 Reset extents Ymin 0 Ymax 10000 d 500 m 20 Zmin 2000 max 0 dz 100 nz m r Processing Options Spatial Vertical sampling interval 100 Memory requirements lt 1MB gt SOFT Expansion Method Mirror UseLanczos Taper Expand horizontally by 100 Save Response Voxet Expand vertically by 400 A Save Expanded Voxet Memory requirements 0 MB Accuracy Estimate The model mesh used for the forward calculations extends from the bottom of the voxet model volume in the current project to the level of the mean elevation of the surface topography This is subject to rounding to the nearest integer multiple of the vertical sampling interval 3D GeoModeller positions the mesh elements laterally such that the observation locations in the
114. the rift Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 5 Contents Help Top 4 Back gt zone some volcanics associated with these faults and crustal thinning where a granite intrusive shows as a gravity high along the axis Ocean crust Magnetic profile Gravity profile as Alkaline igneous ea A E Sng de 2 Pre rift sediments re a ties das wo eyo COMMON CERT ST PE A Se 244 Transitional 3 AL7 2A ocean crust Hiz Magnetic profile e Syn rift sediments SEP o e S e e n Magnetic profile Tholeiitic igneous REE na activily es Moho TE ie Wa r Magnetic profile Gravity profile 32 1 Pre rift sediments Alkaline igneous activity HA Syn rift sediments RNA Tholeiitic igneous activity E3 Post rift sediments ES Axial intrusion Transitional Figure 2 Plan view of the stages of crustal extension Different oceanic crust degrees of extension are accommodated by transfer faults This diagram assumes that that no significant strike slip component Figure 3 Magnetic and gravity expressions of the pre rift and occurs in the extension syn rift stages Sections correspond to sections shown in Figure 2 The figure is taken from Peter Gunn s 1997 paper in the AGSO volume 17 geophysics practice manual Our explorati
115. tigraphic pile missing units allowed Therefore it does not make sense for the stochastic process to explore other possibilities 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 60 Contents Help Top 4 Back gt iG Create Inversion Case Geological Settings Shared Settings Lithology Specific Settings Proposal Lithology Properties 7 Allow Property Change on Fixed Cell s Mice Fix Lithology Frontier J Allow Local Property Difference Check Not Re E Host_rock Constraints Commonality Weibull 0 4 1 0 100 Fd Probability of Property Change Only 50 Shape Ratio LogNormal 0 1 0 1 100 FA Miscellaneous 7 Fix Individual Cells Containing Volume Ratio LogNormal 0 25 0 05 100 rA 4 Surface Intersections Commonality Volume Normal 0 0 1 0 100 A Points from CSV File Browse Always above these Lithologies Any Observed Contacts SA F Selected Observed Contacts 4 Host_rock Granite Unspecified Observed Inferred Interpreted ModelConstructor Select all De selectall Stratigraphic Order Reset lt Bak Next gt Finish Cancel For this tutorial 1 Ensure default unchecked Fix lithology frontiers for all 3 units Because none of our geology boundaries are known with certainty 2 Constra
116. ts Help Top 1 Open the pre created 8D geology project in 3D GeoModeller Launch 3D GeoModeller From the main menu choose Project gt Open OR From the Project toolbar choose Open amp OR Press CTRL O Browse to the pre created 3D GeoModeller project tutorial CaseStudyE TutorialE4 Beginning Project Beginning_P rojyect4 xml 2 Choose Geophysics gt 3D Geophysics gt Inversion Wizard Steps taken are similar to those in the Tutorial E5 below Repeating E5 Tutorial Stages 1 to 4 The main differences are that 1 Joint inversion is not necessary to set single only as geophysics will not be referenced anyway 2 Stage 3 Set Probability of a Property only change to 0 3 Geology changes allowable by the geology tests inversion settings can be viewed and assessed in the same way as demonstrated in Tutorial E5 THIS TUTORIAL IS UNDER DEVELOPMENT PLEASE CONTACT INTREPID GEOPHYSICS FOR FURTHER INFORMATION AND TO ASK THE RELEASE DATE FOR TUTORIAL E4 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 53 Contents Help Top 4 Back gt Tutorial E5 Joint Gravity magnetics litho constrained inversion This tutorial is designed to walk you through a simple practical example of how to set up and runa joint gravity magnetics litho constrained inversion Inversion of your 3D geology model i
117. ts Help Top Note however as the boundary changes the cell with the new geology must use the new property law Locking down the properties can be thought of as a Prior only run see Tutorial E4 with important differences Prior Only seeks to calibrate which settings provide maximum valid levels of geology boundary variation based on your geological knowledge and data sets whilst a Geology Only approach should only be commenced once a close starting model is confirmed because inversion refers only to geophysics to drive solutions within your valid geology envelope already established Setting up geology tests for a litho constrained inversion Aim to specify how and with what constraints geology units can change Without any litho constraints or geology tests inversion can still proceed to an apparent conversion good fit to the geophysics but the resulting models will probably include fragmented geology that bears little relationship to your starting model and are geologically unrealistic In 8D GeoModeller specifications of certain geometric constraints geology tests are available on a lithology by lithology basis so for instance high confidence geology units can be locked down while lower confidence units can be allowed more freedom for the geometry to change An inversion can therefore be set up to minimise unrealistic geology being created for investigation during inversion 1 e the geolo
118. um It is a way of clustering the property across cells 3 Leave the default Probability of property change only 50 Fixing Cells A cell in your model might have fixed lithologies as you are very confident of the geology at that point Typical reasons and ways to control this are good surface geology map hold this constant by fixing all surface outcrop geology cells e borehole logged geology observation at depth fix any cell that has a borehole geology log seismic pick on a section an interpreted point 4 Tick on Fix Individual Cells Containing 5 and choose Surface Intersections tick from the list of options 6 Also select Interpreted below for the provenance of the data in the model Scenario A good surface map scenario applies in this case study We know from field maping that Cover exists everywhere on surface although contact data points for Cover are not actually required on surface to build it that way See Tutorial E1 Also we have confidence in the modelled location of the base of the Cover unit due to detailed interpretation of Electromagnetic EM survey data which was used to constrain the starting geology model Probability of property change only Change Scenario Generation Control Case MCMC For this tutorial keep the default at 50 50 For Monte Carlo Markov Chain MCMC the natural case is to allow for a 50 50 split between changing model at the lithology boundaries a
119. utorial E2 e compute a magnetic response e compute a seismic section response 2 Property Optimization Solve for properties using a bounded least squares fit Tutorial E3 3 Bi Modal Property Only Inversion No proposed body just a proposed density contrast Avery simple geology model with perhaps just 2 units such as basement and an intrusive to see where the blobs form similar to the deterministic methods 4 Fixed Geology Model Property Only Inversion an alternative approach to property optimization 5 Prior Only Inversion Fixed Properties Geology Only Inversion explores only the probability space implied by the geological constraints together with the 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 10 Contents Help Top lt 4 Back gt inversion restrictions set Does not use any geophysics grids to drive the evolution Tutorial E4 e This is very similar to aspects of what is becoming more popular in regional geology studies where attempts are made to characterise the geological uncertainty in the map Geology and densities can change but both must follow reasonable statistical laws and use gravity to constrain results Geology and susceptibilities can change but both must follow reasonable statistical laws and use magnetics assuming induced response only Joint gra
120. ve from Series Poe O e E 6 In Explore select Meshes and Grids gt Hide all Views 7 With SummaryStats_400000 500000 Threshold 90 super vo gt MostProbable selected 8 Right click and select gt Export Surface Shells Input Voxet SummaryStats_400000 500000 Threshold 90 super Input Field MostProbable Output D TEMP_PDAC Tutorial E TutorialES E5Completed_Project Tops_NEWoranite csv Query Type EQ Tops only CSV output Output file for the triangle mesh surface shells Value 1 1 9 Choose query type EQ 10 Tops only for cvs output which can be re imported into GeoModeller as a cloud of contact data points 11 Choose value type 1 1 Granite 12 From the Right side Browse to the directory of your choice to save the file 13 Name the file say Tops NEWeranite gt OK Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 81 Contents Help Top 4 Back gt Surface shells was successful The output CSV file is available at DA TEMP_PDAC_Tutorial_E TutonalES E5Completed_Project Tops_NEWgranite csv 14 Next from the Main menu Import gt 3D Geology interfaces The WIZARD will lead you through the importation of the points from the cvs file to be assigned to the geology object called NewGRANITE
121. version to see what probability space is implied by the geological constraints geology tests that we are going to set We are not concerned in this case with the reduction of the calculated misfit between predicted and observed geophysics no likelihood of the new proposal will be calculated at each iteration nor compared with the reference geophysics grids E4 Steps overview 1 This simple 3D GeoModeller project has already been created for you You can use the same model project from Tutorial E2 or Load the Beginning project of Tutorial E3 from your installation directory 2 First we will set the geological tests which will govern the tightness or looseness of the exploration of geological boundaries during an inversion 3 Next carry out a stochastic simulation calculation 4 Finally evaluate whether our set geological tests result in appropriate variations of the 3D geology model In this section e EK2 Configure and run a fixed properties gravity inversion including setting the geological tests e EK2 Evaluate the extents of the spaces explored between the geological units in the 3D geological during inversion Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 52 Contents Help Top 4 Back gt E4 Stage 1 Create a new Case Conten
122. vised geology model Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd q Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 88 Contents Help Top lt 4 Back gt Tutorial E6 Forward calculation of full tensor gravity grids Parent topic Tutorial case study E Forward and inverse modelling of potential field data This tutorial introduces the user to full tensor gravity grids as a precusor exercise to performing inversion with observed full tensor potential field data the basis of an extension Tutorial currently under development In this tutorial e K6 Introduction E6 Stage 1 Load the BuriedGranite 3D model E6 Stage 2 Forward calculation of a gravity full tensor grid E6 Stage 3 Visualization of the component tensor grids E6 Introduction 1 In this tutorial we will forward model a gravity full tensor field directly from our 3D geology model using a modified Fourier method The result is a 6 band ERMapper BIL grid We will visualise the full tensor grid by the cube root of its determinant Next we will visualize in turn the separate components of the tensor by querying each band using a small grid viewer tool in GeoModeller E6 Stage 1 Load and review the BuriedGranite 3D model Contents Help Top 1 Continuing on from Tutorial E5 with your current project 2 OR from the
123. vity and magnetics exploring geometry only 0 probability of property change e exploring properties only 100 probability of property change exploring both geometry amp properties 50 50 chance of either sort of change Tutorial E5 Joint gravity and magnetics including the possibility of magnetic remanence Forward modelling of the gravity full tensor response Tutorial E6 Inversion of observed full tensor gradients with 5 independent observations or more driving the changes At all stages examine the computed geophysical response grids and compare them to the observed grids Especially in the early stages confirm the main features are present Once you have a near starting model all the inversion methods above will produce quite a good fit The statistical analysis of the thousands of equally viable models is the place where you will learn more about how good your model is at explaining the geology Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt oe atl Manual Tutorial case study E Forward and inverse modelling of potential field data 11 Contents Da ch 7 Yo i DAVNA aversion anlar flowchart This flow chart illustrates the way an inversion session progresses Each pass through the central loop is termed an iteration There are generally many millions of iterations 1n each session Fails Lai SSS ao a _ Isl scald dataset criteria J
124. vity forward calculation Steps e K2 Analyse the forward calculation Steps Configure and run a forward calculation Steps Parent topic E2 1 Select the data type to calculate ecg From the main menu choose Geophysics gt 3D Geophysics gt Forward wizard 3D calenlati on GeoModeller displays the forward calculation area of the 3D Geophysics tool 2 Accept Case 1 and choose Create a new case Choose Gz vertical gravity in the Fields to compute area Create Forward Case Source Select the components to calculate during forward modeling Project Name DAC New case name Case1 Create a new case Clone an existing case Load Initial Lithology Voxet Lithology field Tutorial E TutorialE2E2Completed Project E2Completed Project xm I UWHA y UWHA B L fait Fields to compute vez Vertical Gravity Gravity Tensors Gx Gxy Gxz Gyy Gyz Gzz e a lll Magnetic Tensors Browse Next gt Finis Canel Gz is the vertical component of gravity in mGal the quantity normally measured with ground gravity instruments TMI is total field magnetic intensity in nT the Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 32 lt 4
125. vo Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 71 Contents Help Top 4 Back gt Check the volumetric changes of the granite body in initial vs final inversion models The final vo is already loaded in the Explore tree so now load the initial vo to set up a quick comparison 1n volumetric terms 1 From the Explore tree select Grids amp Meshes 2 Right click Import gt 3D Grid Voxels 3 Browse to and Open initial vo in you results directory CaseStudyE TutorialE5 E5Beginning Project Case2 Run1 initial vo 4 Select and expand the initial vo grid in Explore 5 Select the Lithology field of the initial vo grid and right click gt Histogram Histogram of Lithology Ld Geological Model a 100 Lithology Volume m 5 3975E10 95 1 Cover 1 22925E11 2 31E10 Host_rock Granite Percentage Host_rocl Lithology x Histogram of Lithology E an A _ Volume Geological Model 100 Lithology Volume m 95 Cover 5 5E10 Host_rock 1 28525E11 as Granite 1 6475E10 oo 1 o 1 70 55 64 262 co o bu wm 55 D 50 2 o 45 Q o 40 ac 4 30 27 5 20 154 10 8 238 Y Granite Host_rocl Covel Lithology 3 K
126. y Reference Density g cm B Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 30 lt 4 Back gt Susceptibility ST Remanent Magnetization A m Log normal 2e 005 1e 006 100 Normal o 0 100 0 0 BB Host_rock Log normal 0 002 0 0001 100 Normal 0 0 100 0 0 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd Granite Log normal 0 004 0 0002 WO eNormal o 0 100 0 0 General Parameters Magnetization Total Magnetic Field nT 56600 Dedination degrees 7 6 Indination degrees 62 4 Back gt GeoModeller User Manual Contents Help Top E2 Stage 2 Forward calculation Tutorial case study E Forward and inverse modelling of potential field data 31 lt 4 Back gt We perform a forward model calculation to verify that the combination of a geological model and the properties assigned to each formation produces a response that broadly corresponds with a set of observations We do this as a prelude to the inversion session because we base interpretation of the inversion results on an assumption that the starting model was a reasonable first guess for a model that would be consistent with geological physical property and geophysical observations In this section e EK2 Configure and run a forward calculation Steps e EK2 Lateral padding of a model Information e EK2 Summary images of the response for gra
127. y of the geology 9 Inthe light of outcomes you can revise geology boundaries and physical properties E5 Stage 1 Create a new Case Open the existing 3D geology project in 3D GeoModeller 1 From the main menu choose Project gt Open OR From the Project toolbar choose Open amp OR Press CTRL O Browse to the existing 3D GeoModeller project CaseStudyE TutorialE5 E6Beginning_ Project E5Beginning_ Project xml View the 3D model in the 2D and 3D viewers 2 Choose Geophysics gt 3D Geophysics gt Inversion Wizard i Create Inversion Case Source Select the initial lithology model case and run Case Case name Run Run name Runi Initial lithology model Project lt Use current project gt Voxet Lithology field The wizard will suggest creating a new Case and a new Run labelled by the next sequentially available name Casel already exists in your directory If you prefer to re use a previous Case with an associated discretisation scheme and selected grids you can do this Browsing options to existing Cases will show and GeoModeller will then instead suggest a new sequential Run number for the same Case 3 Choose Next Contents Help Top 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Tutorial case study E Forward and inverse modelling of potential field data 55 Contents Help Top 4 4 Back gt Create Invers
128. y surface to reduce aliasing e Also note the Indicator this shows estimated required memory to run the task E5 Stage 2 Check rock properties distributions This wizard page allows you to check and alter the initial set of rock properties distributions for each lithology in turn You can change a Probability Distribution Function PDF for this lithology by double clicking on the text with the law in it This 1s similar to the same page in the Forward Wizard At the bottom of the wizard page you can choose how density magnetic susceptibility will be applied to the initial model The options are e From Law Mean this is the Default and sets the mean value of each unit to be applied to every cell with that lithology From Law Random this sets the full PDF to be used on startup to give each cell a random sample from the law e From voxet external this allows you to supply and set a voxet with customised properties already described prepared externally Currently you must take care to exactly meet the same project extent and cell size you have specified previously in this wizard Page 2 of the wizard 2013 BRGM amp Desmond Fitzgerald amp Associates Pty Ltd 4 Back gt GeoModeller User Manual Contents Help Top Tutorial case study E Forward and inverse modelling of potential field data 57 lt 4 Back gt An important point to remember is that each lithology has its own unique

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