User Manual for SurfSeis 2.0 - the Kansas Geological Survey
Contents
1. pereg mid station Zero 0 value SE ee indicates an absolute match a o A without any tolerance in ene i rae station numbers between the een pes two OT records to be combined Then click Save Combined OT As dat button to specify an output file name A default file name will have been Phas cine assigned Click OK button i a a in the dialog This will launch the process of Figure 7 4 combining and saving the combined records as they are being displayed automatically one by one If output file was not assigned then the combining process will occur only whenever a new record is selected by pressing any of the four arrow buttons in the top tool panel of the display window References Park C B and Miller R D 2006 Roadside passive MASW Proceedings of the SAGEEP April 2 6 2006 Seattle Washington Park C B Miller R D Ryden N Xia J and Ivanov J 2005 Combined use of active and passive surface waves Journal of Engineering and Environmental Geophysics JEEG 10 3 323 334 Park C B Miller R D Xia J and Ivanov J 2004 Imaging dispersion curves of passive surface waves SEG Expanded Abstracts Soc Explor Geophys NSG 1 6 Proceedings in CD ROM Park C B Miller R D and Xia J 1999 Multichannel analysis of surface waves MASW Geophysics 64 800 808 Schwab F A and Knopoff L 1972 Fast surface wave and free mode computations2. 1 2 for the source offset x and receiver spacing dx respectively Choose meter for the distance unit Make sure ee Source Location has been correctly detected by the a program If not override it manually Then select Source Receiver Move tab and type in station Figure 4 3 number 4000 for the next impact location Make sure the interval between current and next impact locations matches actual value 4 used during the survey Also make sure Moving Direction has been properly selected This direction will determine if the acquisition moved to a direction of higher or lower station numbers Range of records to which current setup applies can be specifically selected if necessary in the two drop down boxes at the bottom of the dialog If multiple rather than one records were saved at the same location before the source receivers configuration SRC was 19 4 mong Deana cael Retief EEA meatus TE ama VK Haw am Figure 4 4 moved to next location then the number in Record s Move edit box should reflect it appropriately with a wssemtm number greater than one Click OK button to close the s a dialog box and then click Run Field Setup to launch the ugysonie roo ose process At the end of the process another window will appear where encoded field geometry is marked Check if xa all the records h
3. It is often useful or necessary to combine together overtone OT records processed from active and passive data sets for two reasons 1 to enlarge the analyzable frequency therefore depth range of dispersion Figure 7 1 and 2 to better identify modal nature of dispersion trends Park et al 2005 Figure 7 2 Procedures to combine two sets of overtone data are explained here Each set may have a different number of constituent records Or they may have the same number of records with an identical record number and mid station sequence like the two sets prepared from active e g 0 2 sec and passive e g 2 120 sec portions of the passive roadside data explained in Chapter 4 For seamless combining it is always recommended but not required to prepare the two sets with the same ranges in frequency e g 5 50 Hz and phase velocity e g 10 2000 m sec and with the same intervals e g 0 2 Hz and 10 m sec increments B Figure 7 1 Figure 7 2 37 Combining active and passive overtone Circular Receiver Array records explained in J 120 m Chapter 4 by using a sample data set 6 r acquired during a passive roadside survey would not provide any significant gain in lower frequency end of the dispersion when compared to the active image This is because of the PE OEA relatively short aaa receiver array D 35 m for a passive survey Or it can Clinton Pkwy 23rd St m also be said that the
4. eo os Figure 3 1 10 reported yet as far as systematic and scientific perspectives are concemed Intensive modeling tests performed at the Kansas Geological Survey KGS however indicated an insignificant difference between different types insofar as the symmetry of the array is maintained It is therefore the convenience of field operation that determines a specific type to be used We include sample data sets acquired with two different types of array cross Passive Cross dat and circular Passive Circular dat types Both sets were collected at the same site but at different times about one year apart and are in KGS format no need to format Each set contains ten 10 records of identical recording parameters Array Dimension D and Receiver Spacing dx Array dimension D is directly related to the longest wavelength Ama that can be analyzed which in turn determines the maximum depth of investigation Zaw D devas Zo en On the other hand minimum if uneven receiver spacing dx is related to the shortest wavelength Ama and therefore the shallowest resolvable depth of investigation Znin dx hmin Zin e n 3 2 Data Acquisition Parameters described here are the ones most commonly used at KGS and by no means represent a required set of values Slight variation in any parameter can always be expected Recording Parameters Please note that the maximum number of samples per trace that can
5. orien E aa It is always assumed during the field setup processing that a road runs west east W E direction and that the receiver array was located at tHi e Pamane Ba the northem side of the road This convention 9 Fo om oom should be noted when interpreting the azimuth Pee information of processed surface waves as explained in section 5 1 Figure 4 6 Once all parameters are set correctly in the graphical setup dialog then close it and click Run Field Setup button at the lower right comer of the main window to start encoding field geometry If multiple records for example ten were acquired at the same array location then specify the corresponding record range e g 5001 5010 to apply the same field geometry with zero 0 interval of array move and then repeat the encoding process with the next set s of records e g 5011 5020 by specifying proper station numbers to reflect the new location for the array Step 4 Generation of Overtone Records Process active and passive data sets eg Roadside Active OT dat and Roadside Passive OT dat separately by following the procedure described in section 5 1 Step 5 Combining Active and Passive Overtone Data Sets See section 7 2 Step 6 Extraction of Dispersion Curves from Overtone Image See 5 2 Step 7 Inversion for 2 D Vs Profile See Chapter 6 21 Chapter 5 Data Processing Dispersion Analysis Once field geometry i
6. Norm Amplitudes box tation number of the combined record is specified in Mid Station edit box with a default value extracted from the current record Any other overtone file can be imported whenever necessary by clicking Import Other OT File button on top of dialog If an imported file also has a multiple number of records then only the record whose record number is the same as that of the current record will be combined if Combine OT s of same record number option is checked Record numbers of current and imported records being combined together are displayed on top of the chart If an imported file has one record this option is ignored Combined record s can be saved by clicking Save Combined OT As dat button Output file will be appended if Append Output option is checked As long as the Combine button remains down combining the two records will take place every time a new record is displayed by pressing one of the four arrow buttons in the tool panel 7 1 Combining One OT with Multiple OT s It is often a practice to run a passive remote survey of a large dimension e g D 100 m at the same site where active data have been acquired The purpose would be to come up with a 1 D Vs profile representative of a large volume of near surface materials defined by the large D and Zmar In this case there will be ultimately one passive OT of the best quality although multiple nu
7. level increases and or total receiver array length D increases Receivers Low frequency e g 4 5 Hz geophones are always recommended Effectiveness of somewhat high frequency e g 10 20 Hz phones however is often comparable to that of much lower frequency ones Vertical instead of horizontal phones have to be used Although spike coupled geophones always give the highest sensitivity the coupling provided by a land streamer can be equally well suited with a significant convenience in field operation Field Geometry Length of the receiver spread D Figure 1 1 is directly related to the longest wavelength Ana that can be analyzed which in turn determines the maximum depth of investigation Zn D danas Zmax 2 1 On the other hand receiver spacing dt is related to the shortest wavelength Ann and therefore the shallowest resolvable depth of investigation Zn dx min Znin 2 2 In practice however Ana therefore D in an active survey is usually limited by the seismic source because it is the primary governing factor It is usually in a few tens of meters e g lt 30 m in most cases The source offset x controls the degree of contamination by the near field effects Its optimum value has been a debatable subject We however suggest a value of about 20 of D e g x 5 m when D 25 m A large value of x e g gt 10 m and a large D e g gt 100 m will increase the risk of higher mod
8. respectively A previously saved dispersion curve file de can also be chosen by clicking the Open button so that a Vs model can be constructed based on the phase velocity wavelength relationship depicted by the dispersion curve Clicking the Run Modeling button will generate dispersion curves to be displayed on top of the overtone image Figure 6 5 Fitting degree of a particular curve with respect to any possible trend in the background image can be judged from the corresponding signal to noise ratio S N curve in the level of individual frequency Its average over the entire frequency range is displayed in the corresponding colored bar graph at the bottom of the control panel Save Current Layer Model will enable you to save values of Vs Vp and POS parameters into separate text files txt in the same format used to construct a 2 D Vs map Specific type s of the output file e g any or all of Vs Vp and POS to be saved will be determined by the checked option s of Output type s explained in the Output section described later Saving Vs values determined through a series of forward modeling will provide a manual inversion with complete control over all the constituent inversion parameters 33 ele o gt EE cm ne ekeeke z Ea y ena Leam le sell tS aa ae rea e mele is Roger 22 SS Figure 6 5 Inversion Parameters related to a
9. they were acquired at different locations by moving the receiver array then the increment should be a nonzero value 7 SASAE indicating different aea representative locations In this case another edit PETES Figure 3 5 14 box Record s Move will appear to a aja specify the mumber of 8 8 8 8 2 fr SE records saved with the Setup button The map of the receiver array encoded in a data set can be displayed whenever necessary by clicking the Show receiver array map button on top of the seismic display window same array at one a i oan location ji ji encoding by Run Field t t ji Figure 3 8 Step 3 Generation of Overtone OT Records See section 5 1 to produce OT records from a field geometry encoded seismic file Note that once the output file of OT records is ready you have two options for the remaining steps of processing to produce a 2 D Vs profile 1 a sequence of extracting dispersion curves and then invert them by following those two steps Steps 4 and 5 explained below and 2 inversion of OT records without extraction of dispersion curves explained in section 6 2 Step 4 Extraction of Dispersion Curves from Overtone Image See section 5 2 Step 5 Inversion for 2 D Vs Profile See section 6 1 Figure 3 8 A nun Fats Sip Figure 3 7 15 Chapter 4 Passive Roadside MASW This
10. usually changing with frequencies and phase velocities with a higher energy level associated with a higher S N this relative energy can be accounted for on evaluating the match if Dispersion and relative Energy option is selected On the other hand the relative energy variation can be ignored and only the overall trend of dispersion can be considered if Dispersion only option is selected In this case the energy of a particular point on the image is normalized first along the phase velocity axis during the evaluation In the case of multi modal inversion specified in Dispersion tab in Modeling Figure 6 4 the relative weighting of individual mode can be specified in Weighting of Dispersion Curves box 2 D Vs Mapping If the input overtone file contains more than one record the inversion can be applied to all records if All Records option is checked to come up with a 2 D Vs map A specific range of records to process can also be set Random option in Starting Layer Model radio box will make the inversion of each overtone record completely independent of each other On the other hand Previous model inverted will make the subsequent inversion of the next record start with the inverted layer model of current record as an initial layer model Clicking Run Inversion button will launch the inversion process Dispersion curve s best matching as of current the trends in the overtone ima
11. Phase Velocity Searching Angle ontrast Records and Algorithm In the case of active data Searching Angle tab will be missing whereas the tab will be besa missing in the case of passive data Each page is Figure 5 3 explained below Frequency and Phase Velocity Ranges and intervals of phase velocity and frequency of the output OT data to be generated can be specified in this page of dialog Computation time will directly increase as ranges increase and or intervals decrease In the case of active data there will be an additional box called Offset Range to Process Specifying non zero values for minimum and maximum offset edit boxes will make the wavefield transformation offset dependent For example MIN 5 m and MAX 50 m will include only those data within the specified offset range in the transformation On the other hand MIN 100 and MAX 500 will select only those offset ranges within 1 5 times the wavelengths 2 s of calculation in the transformed space For example calculation of transformed energy at 20 Hz for a phase velocity of 200 m sec i e 2 10 m will select offsets in the 10m 50m range Searching Angle This page will appear only with passive data sets passive remote and passive roadside ones Searching quadrants can specify the angle range 0 360 positive clockwise from north of incoming surface waves Specifying limited quadrants rather
12. a processed dispersion image usually lacks information at shallower higher depths frequencies Although in theory this missing information can be filled through multiple surveys with progressively smaller dimensions D s higher frequency components of passive surface waves may not be recorded effectively because of their relatively rapid attenuation properties The best way would be to perform a separate active survey preferably at the array center by using a sledge hammer Then two separate dispersion image data sets can be combined together to form a broader band image An alternative approach to replace the need of a separate active survey would be to apply active impact s at a place close to but outside the receiver array during the recording of a passive record Following constraints however are to be considered in this case Analyzed shear velocity Vs information at shallow depths can only be associated with those near surface materials near the impact point Analyzed dispersion trend for those high frequencies generated by the active source can be slightly distorted at most 10 because of violation of the plane wave assumption Dispersion image for those low frequencies of passive waves can be adversely influenced resulting in a degraded definition or slightly distorted trend or both A more detailed study on this issue has been planned at KGS and will be reported soon Reports of experimental results fro
13. active source was effective enough to Figure 7 4 generate surface waves as long as the array dimension The importance of longer array dimension for recording longer lower wavelengths frequencies of passive surface waves can be illustrated by using another set of sample data stored as Passive Roadside LongerArray dat in KGS format It consists of ten 10 120 sec field records acquired by using a 24 channel linear receiver array with 5 m spacing d 5 m deployed about 5 m north of the survey line used for the acquisition of passive roadside data 4000 dat 4009 dat Figure 7 3 All ten 10 records were then encoded with proper field geometry and then processed for the overtone records with the Stack Same Mid Station OT s option checked see Figure 5 1 The passive image in Figure 7 1 shows this image whereas the active image is one of the ten active images processed from the active portion e g Roadside Active dat of the data as explained in section 4 3 Users are encouraged to process the sample data and go Z lowa St Passive Roadside Surveys through the combining N process explained later A ES ema omes The active image in a E Figure 7 2 was obtained Tom WER cca by processing an active mm Seadsice Rol Aona y pi g Chamet 2 3 seo 282830 Survey record Land Streamer Passive Active at Chion Phy center dat acquired at the center of the cir
14. be processed with SurfSeis is limited to 32000 which is more than enough in most cases as explained below Sampling nterval of 4 ms dt 4 ms and total recording time of 30 sec T 30 sec are most commonly used at KGS when surveys are performed inside the city of Lawrence Total recording time T s determined in such a way that there is at least one occurrence of passive surface wave generation during recording Therefore it can be reduced or increased depending on local situations related to the surface wave generation In case of surveys of nearby roads for example there should be a vehicle passing near the survey area at least once during recording The longer T is not always better This is because the chance of recording surface waves generated at different locations on the road increases as well and it will in general degrade the data processing resolution unless those locations are well apart in azimuth for example 90 or more If the main source point is fixed in location however the longer T will be better This case of fixed source point of major surface waves can be noticed when you hear a loud jolting sound coming from fairly the same spot on the road as a vehicle passes over Vertical stacking during recording is strongly discouraged unless T is significantly limited because it will increase the change of recording multi azimuth surface waves explained previously Instead it is recommended to save individual r
15. both types of data one in KGS and the other in JPEG format respectively saved separately at the time of saving dispersion curve Checking Show All Energy Peaks option will display all energy peaks at each frequency and can be useful to visualize details of hidden dispersion trends Max Display of Saved Curves option specifies the number of the concurrent display of previously saved curves as the extraction process continues 28 Ilustration of Curve Extraction with Sample Data Some practical issues related to the curve extraction are illustrated through a display Figure 5 7 of overtone images processed from a sample data set with extracted curves overlapped wan Svelte Active ActiveOT Vs GRD Surface Location Station Number 1020 1050 1040 1050 lu ude A Locatonof Ds Profle Used Figure 5 7 continued 30 Chapter 6 Data Processing Inversion Analysis Inversion is the last step in data processing with SurfSeis Either a 1 D or 2 D shear velocity Vs profile is obtained at the end of the inversion process depending on whether single or multiple dispersion curves or overtone records are processed Two different types of inversion are available the one working on extracted and saved dispersion curve s and the other working on the overtone OT image The former type is a gradient based iterative method by Xia et al 1999 and i
16. the burden of securing an wide open space for the array This can be a good choice if a relatively regional one dimensional 1 D Vs profiling is needed The passive roadside MASW method Park and Miller 2006 adopts the conventional linear receiver array and tries mainly to utilize those surface waves generated from local traffic It tries to overcome limitations with the passive remote method such as difficulty in securing a spacious area and inconvenience in field operations by sacrificing the accuracy usually less than 10 of the Vs evaluation With this method the array can be set along the sidewalk or the shoulder of a road and the survey can continue in a roll along mode for the purpose of 2 D Vs profiling Using a land streamer for the array can improve the survey speed by as much as a few orders of magnitude In addition an active impact e g by using a sledge hammer can be applied at one end of the array to trigger the long e g 30 sec recording of data This can result in the active passive combined analysis of surface waves for the purpose of obtaining both shallow e g 1 20 m and deep e g 20 100 m Vs information simultaneously A more detailed description of each method can be found in previously cited references However field procedures for these methods both passive and active have been summarized in this version of manual Data processing steps are explained by using the sample data sets stored in the SurfSeis20 Sampl
17. the correct locations according to the previously specified parameters New Array button in the top tool panel will always enable you to go one step back so that you can change some of the previous parameters To change chart axis scale and attributes of grid lines click Controls button in the tool panel If you have an already saved array you can import it by clicking Import Array button To change a receiver location click and drag it to the proper coordinate Once all the receivers are correctly positioned on the chart you can close the chart and then it will ask you to save the array Next step is to specify the reference station number for the center of the receiver array Figure 3 7 It can be an arbitrary number of your own invention It is used to assign a unique surface coordinate to the inverted 1 D Vs profile that will be obtained at the end of data processing Increment per record applies only when input file contains multiple records acquired by using exactly the same array but at different sites In this case it will assign a different station number to each record by incrementing a e afs o S a gal n a ey certain number from the seve coe uote Jae am gard ee one used for the previous PECENER ARRAY SAVED NEM record If all those multiple records in the input file were acquired at the same site it should be zero 0 to assign the same station number to all the records Instead if
18. SurfSeis Active and Passive MASW Seismic Processing Software for use with Microsoft Windows Supplementary User s Manual v 2 0 Surf Seis tit by Choon B Park and edited by Marla Adkins Heljeson November 2006 Kansas Geological Survey 1930 Constant Avenue Lawrence Kansas 66047 3724 USA Phone 785 864 3965 2176 Fax 785 864 5317 E mail SurfSeis kgs ku edu www kgs ku edu sofiware surfseis index html Chapter 1 Chapter 2 21 22 Chapter 3 3 1 3 2 33 Chapter 4 4 1 42 43 Chapter 5 5 1 5 2 Chapter 6 6 6 2 Chapter 7 71 72 References Table of Contents Introduction Active MASW Data Acquisition Data Processing Passive Remote MASW Receiver Array Data Acquisition Data Processing Passive Roadside MASW Receiver Array Data Acquisition Data Processing Data Proc sing Dispersion Analysis Step Processing for Overtone OT Image Data Step 2 Extraction of Dispersion Curves from OT Image Data Proce sing Inversion Analysis Inversion of Dispersion Curve Inversion of Dispersion Image Combining Active and Passive Overtone OT Records Combining One OT to Multiple OT s Combining Multiple OT s of Passive Roadside Data Chapter 1 Introduction Since the release of SurfSeis version 1 0 in 2000 the surface wave method in general has gone through a tremendous amount of applications and research at many places including the Kansas Geologi
19. at They were acquired along the Clinton Parkway Figure 4 1 in Lawrence Kansas by using a land streamer consisting of thirty 30 4 5 Hz geophones installed with 1 2 m separations A 48 channel acquisition system was used to record field records 4 ms sampling interval Eighteen 18 traces out of 48 traces will therefore have to be discarded at the beginning of processing as explained later After recording one 120 sec 2 minutes field record triggered by an active hammer impact Figure 4 1 the streamer was moved by four stations 4dr towards the east to be ready for acquiring the next field record The impact was applied at four stations 4dx away inline from the west end of the streamer Therefore only one field record was obtained at a given location of the array and the advantages of acquiring multiple for example ten field records at the same place explained in section 3 were not tried at the time Obviously the fairly short receiver spacing dx 1 2 m with 30 channel acquisition D 35 m was not optimal for a passive survey aiming at deeper for example Zn 100 m depth of investigation as the land streamer was designed mainly for active surveys A longer spacing for example dx 3 m would have been highly preferable Step 1 Formatting Go to Utility gt Format and then select all ten 10 records 4000 dat 4009 dat in SEG 2 format Specify output file name e g Roadside dat and then click R
20. ave been correctly encoded Active data set has now been field geometry encoded Figure 4 5 Now open the passive data set e g Roadside Passive dat Make sure to choose Passive and Roadside in the survey type dialog box Figure 4 5 A different graphical dialog box will appear Figure 4 6 Type in station numbers for the first two traces of the field record displayed in the background These numbers however should be those values used for the active data set Figure 4 4 Type in the channel number of the first trace usually 1 receiver spacing and then select a range in offline offset which is an approximate distance between the array and road center see Searching Angle in section 5 1 Receiver Array Move indicates the distance in number of stations that the array moved after acquiring data at a given location It can be or depending on the direction of its move and the way stations are defined for example whether it increases toward left or right direction in the first two yellow edit boxes This should match Source Receiver Move interval used in the field setup for the active data set previously encoded In the case being demonstrated here it has to be 4 The Record s Move edit box indicates the number of records repeatedly saved at the same z location before the source receivers configuration EEEren EF 5 Comi m m 2 SRC was moved to the next location SOs 8 See
21. cal Survey KGS In consequence SurfSeis 2 has new features that take into account those new methodological developments as well as users demands for enhanced user friendliness Although the manual Manual20 pdf has been prepared mainly to explain the new features such as those related to the passive part of the multichannel analysis of surface waves MASW method it can serve as a stand alone manual for both active and passive MASW methods for those who have previous experience in seismic ig in either body or surface wave methods Other information dealing tored In this manual the MASW method has been divided into three categories by survey mode active passive remote and passive roadside MASW methods Figure 1 1 The active method Park et al 1999 was introduced in previous versions of SurfSeis It is the conventional mode of survey using an active seismic source e g a sledge hammer and a linear receiver array collecting data in a roll along mode The other two methods utilize surface waves generated passively from ambient cultural and natural activities such as traffic and thunder tidal motion atmospheric pressure change etc The passive remote method Park et al 2004 2005 employs a two dimensional 2 D receiver array such as a cross or circular layout to record passive surface waves This results in the most accurate evaluation of shear wave velocity Vs at the expense of more intensive field operation and
22. cular p array Figure 7 4 used Figure 7 3 38 during the survey for the Passive Circular dat illustrated in section 3 3 The active survey used a 24 channel receiver array with 0 6 m receiver spacing dx and source offset x A combining module is included in the top tool panel of the dispersion display window Figure 7 4 First open a file of overtone record s by using the Open button in the tool panel and then click the Combine button to import another file of overtone record s After display of input data attributes a control dialog will show up Figure 7 4 The record number of the overtone data displayed behind is shown in Current RCD box whereas that of the data being imported is shown in the Imported RCD box Detailed and comparative description of data attributes can be displayed by clicking the Details button at the lower right side of dialog The as they are option in Combine box will make two records combined as they are without any pre conditioning applied whereas after normalization option will apply a certain type of normalization specified in the next box of Norm Options The Global option of normalization will apply the normalization with respect to the maximum value of all the data samples in one record whereas Frequency option applies with respect to one frequency Normalization amplitudes of the two records can be separately specified in
23. d at KGS and by no means represent a required set of values Slight variation in any parameter can always be expected Source A fairly heavy sledge hammer e g 10 Ib will be a good choice Although any other type e g a weight drop that can deliver more impact power into the ground can be an advantage over a sledge hammer because of its capacity of generating lower longer frequencies wavelengths of surface waves the gain is often not enough to warrant the cost of equipment and inconvenience in field operation Using an impact plate also called base plate will help the source impact point become less intrusive into soil Detailed study on the role of the base plate in surface wave generation has not been reported yet and needs to be undertaken in the near future Recently it has been reported that a non metallic plate e g a firm rubber plate can generate noticeably stronger energy at the lower frequency e g lt 10 Hz part of surface waves than the conventional metallic one Vertical stacking with multiple impacts can suppress ambient noise significantly and is therefore always recommended especially if the survey takes place in an urban area Optimum number of stacking can be determined when there is little change in signal to noise ratio S N in the displayed seismic record during the stacking We often use three five vertical stacks at the Kansas Geological Survey KGS This number however should increase as ambient noise
24. ds specified in the previous step Figure 5 4 You can edit the curve if necessary by clicking the Edit Curve button in the top tool panel In a short summary of how to edit the curve click a point to delete click anywhere between two consecutive points to add a point click and drag to move and draw a rectangle to delete multiple points inside the rectangle Whenever you find it is necessary to modify the bounds for a better extraction you can do so by de pressing and pressing again the Bounds button clicking twice normally Save This will enable you to save the extracted curve with its own name Default name will be the input overtone file name with corresponding record number appended at the end for example Active 1000 de Once the extracted curve is saved then the program will show the next overtone record being ready to repeat the previous steps In most cases the bound curves previously established will be reusable without any modification and you can start from the extraction step In the case of data acquired through the roll along mode active and passive 26 et oeneny OR UVTVUY 52a a Pacera 100 yVVTVIVY H Figure 5 5 roadside cases the station mid station of the original field record will be marked as processed in the upper station chart after saving Once all the overtone records are processed and their dispersion curves are saved you can mov
25. e to the next step of inversi is explained in Chapter 6 Inversion button Inversion analys Controls Clicking this button will show a separate dialog box where parameters related to dispersion extraction and some of the display attributes can be controlled Figure 5 5 Number of data points determines the total number of points constituting the extracted curve It is to be noted that the greater number of data points does not always lead directly to an increased accuracy in the subsequent inversion process Instead it will simply increase the computation time of the inversion process Any number between 20 and 30 should be most optimal Curve smoothing applies a moving window linear regression to the preliminary set of data points extracted from every frequency sample in the overtone data to come up with the most accurate dispersion trend The extracted curve displayed is then obtained through a down sampling decimation of the preliminary curve The higher value of curve smoothing will use a larger moving window and will generate a more smoothed curve Clicking Equal wavelength frequency interval option mn analysis by clicking the Eee vmematvcorae F Figure 5 6 will make the frequency interval vary with frequency dense at low and coarse at high frequencies Save Overtone Record and Image options in Save and Display page will enable you to have
26. eData folder All acquisition parameters for the sample data sets are listed in Table 1 1 A summary of the entire procedure with a MASW method active or passive is displayed in the flowchart in Figure 1 2 Major changes and new features with this version are summarized as follows 1 Modules to process passive surface waves have been added in addition to the previously existing active module Figure 1 1 Two different types of passive surveys are available one called the passive remote MASW method uses a two dimensional 2 D receiver array and the other called the passive roadside MASW method uses the conventional 1 D linear array The way dispersion analysis is executed has been changed so that the previous sequence of Preprocess gt Overtone gt Run Save has been divided into two separate steps 1 generation of dispersion image called overtone OT data and 2 mouse aided extraction of the dispersion curve from the image The previous sequence however can still be accessed by right clicking instead of normal clicking the Dispersion button in the analysis menu when importing an input seismic file A new mode of inversion has been added This is a general Monte Carlo method applied directly to the dispersion image instead of the dispersion curve seeking the best matching solution through a random search With this mode up to four modes of dispersion can be accounted
27. eceiver Move tab and type in station number 1005 for the next impact location to reflect the interval 5 between current and next impact locations used during the survey Also make sure Moving Direction has been properly selected This direction will determine if the acquisition moved to a direction of higher or lower station numbers Range of records to which current setup applies can be specifically selected if necessary in the two drop down boxes at the bottom of the dialog If multiple rather than one records were saved at the same place before the source receivers et Rein weir gt E seweetacnion gt Sd he on 1S T Rome Fon Kowal vo Figure 2 5 Figure 2 6 configuration SRC was moved to the next location then the number in the Record s Move edit box should reflect if appropriate with a number greater than one Click OK button to close the dialog box and then click Run Field Setup to launch the process At the end of the process another window will appear where encoded field geometry is marked Figure 2 6 Check if all the records have been correctly encoded The active data set has now been field geometry encoded This table can be accessed later whenever necessary by clicking the Table of source receiver stations button on top of the seismic display window Figure 2 7 Flexibilities with Field Setup Although it is recom
28. ecords separately Then the dispersion imaging process can be applied to an individual record and then these image records 1 can be vertically stacked together to enhance the definition of an image However if T is limited to such a short time e g lt 30 sec by the recording device then a few times of vertical stacking eg stacking 10 sec recording three times may be necessary either during recording or post D and dy will approximately determine minimum number of channels needed In any case however the more channels will be an advantage that can increase the resolution of dispersion processing to a certain degree Forty eight channel is most desirable for a survey aiming at Zma 100 m When only a smaller number of channels are available e g 24 data acquisition can proceed with an array of smaller dimension e g D 25 m and then with progressively larger dimensions g D 50 m 75 m 100 m etc to cover a broader range of wavelengths 2 s In this case dispersion image data sets processed separately can be combined together to construct a broader band dispersion image see Chapter 7 If dynamic range is a controllable option with a recording device choosing the highest value along with the highest gain if available also will always be a benefit Necessity of Separate Active Survey Because a passive survey usually operates with a much larger receiver spacing than normally used in an active survey
29. ent increment I option when checked HEL ea will make the frequency 2 ntl mses La interval vary in such a D Beneeeeiemees eae manner that the interval Ewes Zamwse E monies of a corresponding Boece seve Bpercunienon_ wavelength becomes fairly constant It will Figure 6 4 make the frequency interval denser at lower frequencies and coarser at higher frequencies Save dispersion curve files option will save if checked individual curves separately Thickness depth of the model can be specified in H tab by moving slide bars assigned to each layer Figure 6 4 Thickness H and depth Z of each layer are automatically updated in the corresponding edit boxes as a slide bar changes its position An exact value can also be typed in any edit box Velocities Vs and Vp and Poisson s ratio POS of each layer can also be specified in the same manner by using slide bars in its own tabbed page Because all these three parameters are linked together their mutual dependency can be objectively set by choosing either Update Vp or Update POS radio button Figure 6 4 Vp will be updated if Update Vp is chosen whenever Vs or POS changes whereas POS will be updated if Update POS is chosen whenever Vs or Vp changes Open and Save buttons in the top tool panel will enable you to save the current set of layer parameters in a text file LYR and to import a previously saved file LYR
30. es domination and reduce S N for the fundamental mode The following values are most recommended x 5 m dx 1 m or less and D lt 30 m 23 Interval 4SRC of Source Receivers Configuration SRC Movement An interval between Idx 12dx is recommended 4dx is most commonly used in the case of 24 channel acquisition Recording Parameters One millisecond dt 1 ms of sampling interval is most common with a 2 sec total recording time T 2 sec Use a smaller dt e g 0 5 ms if any body wave processing e g refraction and reflection is planned as by product s In the case of extremely low velocities e g Vs lt 100 m sec a longer T e g 4 sec will be a better choice In any case an excessively long T e g T gt 5 sec is discouraged because it can increase the chance of recording ambient noise e g traffic Usually 24 channel acquisition will be optimal If 48 channel acquisition is available it is recommended to shorten dy rather than to increase D 2 2 Data Processing Procedure of processing an active data set is explained by using a sample data set stored in SurfSeis20 SampleData Active folder Ten field records of 24 channel acquisition were acquired over a soil site near a highway and saved with file names of 1000 dat 1009 dat Figure 2 3 Source offset of 5 m x 5 m along with a receiver spacing of 1 m dx 1 m were used and the source receivers configuration SRC moved by five station i
31. et up receiver array parameters will appear Figure 3 4 Number of channels will show the correct value detected by the program Dimension is the approximate diameter of the array In the case of circular array however type Choose circular Passive Circular dat or Non circular Passive Cross dat for There will be some additional parameters to be specified in the case of circular array to specify relative location This specification becomes critical only for the in the correct value of the actual diameter each data set of each individual receiver along the circle Cross Receives Array n D gt 120m laten Pow zara su Circular Receive Array D120 m inion Pwy EZET Figure 3 2 ie xel Figure 3 3 azimuth information of analyzed passive surface waves telling which direction passive surface waves came from 13 Once all array related parameters except for the location information are specified then a x y grid chart window will appear Figure 3 5 where receivers of all channels are ready there el to be manually edited for their correct locations All tele receivers will have been aligned in the upper half of the chart window with Edit Array button pressed Figure 3 5 To move a receiver of a particular channel a numbered circle click and drag it to the proper location in the chart In the case of circular array Figure 3 6 they will have been already positioned at
32. for and all the parameters in a five layer earth model can be manually changed if desired to compare theoretical curves with dispersion trend s in the background image Most if not all of the bugs existing in previous versions of SurfSeis have been fixed thanks to the comments and reports from many practitioners who used SurfSeis to conduct the MASW method and who were very patient and always into a better form We willing to help this quite new geophy il method Active MASW j Roos m E an e Passive Remote MASW if Cmon Phy ETET Passive Roadside MASW Lineat Receiver Atay Paes Geta k irpact pitt trager coring Figure 1 1 ll in its infancy evolv researchers at KGS sincerely appreciate your patience and assistance Data Acauisition SEG 2 Format a Data Conversion KGS Format Utlty gt Fomat Y Encoding Field Geometry Utlity gt Field Seup Y Dispersion Analysis Step 1 Dispersion Imaging Analysis gt Dispersion Dispersion Analysis Step 2 Curve Extraction analysis gt Dispersion Y Y Inversion Inversion Dispersion Image Based Gracient Based Iterative Monte Carlo Approach Approach Analysis gt Inversion Anolis gt Inversion S Velocity Vs Profile or 2D See Chapter 2 for active Chapter 3 for passive remote and Chapte
33. ge will be displayed on top of the image 35 and will be updated if a better match is found Layer parameters responsible for displayed curves are also reflected in the corresponding tabbed pages in the Modeling page whenever a better match is found Output Layer model parameters Vs Vp and POS can be saved separately by checking Save output txt box Figure 6 7 A file save dialog will show up with a default file name e g Input OT txt assigned to be used as a common part of the individual output file For example Vs values will be saved with a file name of Input OT Vs txt Vp values Input OT Vp txt and so on Surface coordinates of the output data can be set in Station surface coordinate edit box that will have been assigned with a value previously encoded in the overtone record Specific types of output data e g Vs or Vp can be selected in Output type s box Strategy of Inversion It is recommended to first start with several or many manual attempts to come up with a layer model that gives dispersion curve s of fairly good match by manipulating individual parameters in Modeling Then choose perhaps after saving the layer model Start from current model in modeling tab in Inversion before launching the inversion proce ees iin oe a sees mannna OTE Figure 6 7 36 Chapter 7 Combining Active and Passive Overtone OT Records
34. in Bolt B A Ed Methods in computational physics Academic Press 87 180 J Miller R D and Park C B 1999 Estimation of near surface shear wave velocity by version of Rayleigh waves Geophysics 64 691 700 x 40
35. ion image by accounting for the possible initial phase of surface waves at the time of generation This method however may result in significant computational artifacts Evaluation Integrity that appears when the Advanced algorithm is selected will determine the searching degree for the phase relationship of surface waves and will directly increase computational time 5 2 Step 2 Extraction of Dispersion Curves from OT Image A fundamental mode M0 dispersion curve is extracted from each overtone image in the output file saved in the previous step The extraction first requires identification of the MO trend among multiple modes possibly existing together It is usually the one starting at lowest frequency with lowest phase velocity for a given frequency The lowest fa and highest fas frequencies of the curve will determine the range of investigation depth Znax and Zm respectively through the following relation Zmax Amax Cmax fmin and Zmin Amin Cmin I fax 66 1 where Cmax and Cni are phase velocities at fni and fans respectively Each extracted curve will usually have different frequency depth range and the final 2 D Vs profile will show an average range with a proper spatial interpolation applied Go to Analysis gt Dispersion and then select the overtone OT image data previously saved in Step 1 After display of data attributes the first overtone record in the input file will be disp
36. ion image data sets processed separately can be combined together to construct a broader band dispersion image see Chapter 7 Because of the 1 D nature of the array usually 24 channel acquisition may be used to aim at Zma 100 m with dx 5 m A 48 channel acquisition however will be advantageous with an increased resolution in data processing especially at higher shallower frequencies depths If dynamic range is a controllable option with a recording device choosing the highest value along with the highest gain if available also will always be a benefit Necessity of Separate Active Survey Instead of a separate active survey use a sledge hammer to apply an impact at a certain inline distance away from one end of the array to trigger a recording of for example a 30 see long record Figure 4 1 Then take the earliest few seconds for example 0 2 seconds of the record at the beginning of data processing to make a separate active data set whereas take the 7 remaining portion for example 2 30 seconds as the passive data set as explained in the Data Processing section following In this case analyzed Vs information at shallow depth will be biased towards the impact location 43 Data Proces g The overall procedure of data processing is explained by using a set of sample data stored in SurfSeis20 SampleData Passive Roadside folder There are ten 10 field files 4000 dat 4009 dat in SEG 2 form
37. is a passive mode of survey that can be implemented with a conventional linear receiver array Figure 4 1 Although it can result in a certain degree usually less than 10 of overestimated Vs values in comparison to the 2 D receiver array see Park and Miller 2006 this survey mode can result in a great utility because of the convenience in field Roadside Passive Survey 4 u opantion thut d dot Feat Paang La Su aia soccer Pai EA require a large open area for receiver deployment In fact the survey can be Receiver Aray Move a de repeated by progressively esoe soo mp moving the receiver array by a certain consistent distance along the road Siniy the roll along survey mode so that a 2D Ve gt Impact to tager 120 96 recording profile can be obtained Procedures of data Figure 4 1 acquisition and processing are explained below 4 1 Receiver Array A linear array deployed along the roadside will suffice Although it does not have to be close to the road it is recommended to maintain the offline distance between the array and the road center fairly constant for example within 30 throughout the entire survey Array Length D and Receiver Spacing dx Array dimension D is directly related to the longest wavelength Amn that can be analyzed which in tum determines the maximum depth of investigation Zaa D hous Zoas 4 1 On the other hand minimum if uneven receiver spacing dx is related to
38. is fixed in location however the longer T will be better This case of fixed source point of major surface waves can be observed when you hear a loud jolting sound coming from fairly the same spot on the road as a vehicle passes over Vertical stacking during recording is strongly discouraged unless T is significantly limited because it will increase the chance of recording multi azimuth surface waves explained previously Instead it is recommended to save individual records separately Then the dispersion imaging process can be applied to individual records and these image records can be vertically stacked together to enhance the definition of an image However if T is limited to such a short time e g lt 30 sec by the recording device then a few times of vertical stacking tacking 10 sec recording three times may be necessary either during recording or post D and dx will approximately determine the minimum number of channels needed In any case however more channels will be an advantage that can increase the resolution of dispersion processing to a certain degree Forty eight channel is most desirable for a survey aiming at Zmay 100 m When only a smaller number of channels are available e g 24 data acquisition can proceed with an array of smaller dimension e g D 25 m and then with progressively larger dimensions g D 50 m 75 m 100 m etc to cover a broader range of wavelengths 2 s In this case dispers
39. layed and a new set of buttons will appear on the left side of the window Figure 5 3 The task of each button is explained below in actual order of implementation Bounds This button will enable you to establish lower and upper limits of phase velocities for the dispersion curve to be extracted While this button is down click several 5 10 reference points on top of the dispersion trend that you identify as the fundamental mode M0 Figure 5 3 The first and last points will determine the frequency range of the dispersion curve A pair of solid curves will be drawn as reference points are marked and they represent lower and upper limits bounds of the phase velocities to be extracted for the curve If bounds setting was made previously during a previous running of the program you can import the saved setting upon clicking the button 25 You can edit reference points either by click and dragging to move one point or simply clicking to delete Bounds can be changed by click and dragging one nodal point marked with in a bound curve You can only move it along the vertical phase velocity axis It is advised not to make excessively rapid mouse moves during the editing procedure because the mouse response time varies and the program can sometimes skip certain mouse commands if they are delivered too fast Figure 5 4 Extract Clicking this button will extract a dispersion curve most likely within the boun
40. m practitioners are always welcome 12 3 3 Data Processing Overall procedure of proces g passive data acquired with a 2D receiver array is explained by using two sample sets stored in SurfSeis20 SampleData Passive Remote folder Passive Circular dat and Passive Cross dat Both were acquired at the same site Figure 3 2 using a 48 channel cross and a 24 channel circular array respectively Recording parameters are listed in Table 1 1 Step 1 Formatting Ten records were recorded on each survey with original file names of 2000 dat 2009 dat for the cross array and of 3000 dat 3009 dat for the circular array all saved in SEG 2 format Then each set of 10 records was formatted and grouped together to form a single file of 10 records in KGS format with the above names Therefore both data sets are in KGS format and don t need further formatting Step 2 Field Setup Please note that it is the relative coordinate of each receiver that needs to be specified in the field setup procedure with a passive data set and that absolute values of coordinates have no meaning Go to Utility in SurfS and then choose Field Setup tab Import either of the two sample data sets Passive Circular dat or Passive Cross dat A dialog box asking for the survey type will show up Choose Passive and Remote Figure 3 3 is main menu Then another dialog box to s
41. mbers g ten of field records may have been acquired On the other hand the number of active overtone records will be many e g 10 or more representing dispersion characteristics of shallow materials at different locations but within D of the passive survey In this case combining the same passive overtone record with all active records for the purpose of selecting a combined record of most appropriate quality may be tried First open the active overtone file by clicking Open button on the top tool panel of dispersion display window Figure 7 4 and then click Combine button to import the passive file After options are properly set then click OK button in the control dialog The imported OT record will be combined with every OT record in the active file on display as long as the Combine button remains down 39 7 2 Combining Multiple OT s of Passive Roadside Data Open the active overtone file prepared from the procedure described in Chapter 4 by clicking Open button in the top tool panel of dispersion display window Figure 7 4 Then click Combine button to import the passive file prepared from the same procedure A control dialog will show up Figure 7 4 Make sure Combine OT s of same Mid Station s option is checked Tolerance of station s appearing right below this option indicates the degree of proximity in terms of station numbers that can be treated as the same
42. mended to acquire data in a roll along mode by maintaining the same source receiver configuration throughout the entire portion of a survey line such deviations as redundant or skipping of recordings at certain places changing source offset x and or receiver spacing dx etc may always occur Or sometimes one may attempt to process surface waves recorded during a body wave survey e g refraction or reflection survey Accounting for most if not all of these unusual circumstances can be made by a proper manipulation of the Record Range To Apply Figure 2 8 and Fixed Receiver Array Figure 2 5 esd lee D cearseimensoFe bata hal wel Sete fara sumina gt Siar un Fits Sai Figure 2 8 and 2 8 options The latter option does not move when checked the location of receivers although the source location may do so within a specified record range Whenever an inconsistent field setup is applied it is always recommended to specify a separate output file on st setup and then to append subsequent records of different setups to the specified file Step 3 Generation of Overtone OT Records See section 5 1 to produce OT records from a field geometry encoded seismic file Note that once the output file of OT records is ready you have two options for the remaining steps of processing to produce a 2 D Vs profile 1 a sequence of extracting dispersion curves and then inverting them by following th
43. n automatic iterative Monte Carlo inversion method are grouped here Figure 6 6 This method of inversion searches for a five layer earth model whose dispersion curves best match those trends in the image It is automatic because the searching is performed on its own without user s intervention iterative because the searching is repeated to update the eine men tame stg sn ne tri at ims ete tomas pean Beers sa e fea Fo mF ae es fees Temas eae as wor ana SES lt a rae vee IE erin Sei El e ma aes Soy wr mayorga EE Nil reman ndas 11 ne Aea ae ss a E nm in Figure 6 6 34 model and a Monte Carlo method because the searching is a random process This page of controls has another set of two tabbed pages of General Parameters and 2 D Vs Mapping If the input overtone file has only a single record the 2 D Vs Mapping tab will be missing General Parameters Those parameters related to general aspects of the Monte Carlo i are grouped into three different tabbed pages Search Option Layer Model and Matching version Open Search option in Search Options tab sets if selected allows the searching range of layer parameters to be wide open whereas the other option Search from current model in modeling tab uses the parameters specified in Modeling tab as an initial model to start from Figure 6 4 Whe
44. n the latter option is chosen another set of parameters will be shown Limit velocity Vs change sets bounds in 4 in all layer parameters of the current model within which new values are to be searched Depth parameters H and Z are set to current values and not updated if Fix depth Z model option is checked Maximum number of random searches can be set in Search Intensity box 100 corresponds to 500 times of trials Searching ranges in depth Z and velocities Vs and Vp can be specified in Layer Model tab Depth Z here means the depth to the top of the half space which is normally referred to as maximum depth of investigation Zmay This option becomes effective only when Fix depth Z model option is not selected Searching range of Vs is specified in the two MIN and MAX edit boxes on the right side of the Velocity Vs label Vp and POS are updated accordingly through the relation set from Update Vp or Update POS option in Modeling tab Velocity Vs increase with depth specifies a relative increasing degree in Vs change with depth Zero 0 will remove such bias to make the Vs changing trend completely random whereas 100 will make it an absolute increase with depth latching tab shows options used to evaluate the matching degree between modeled curves and background image Figure 6 5 Because a trend of dispersion in the image has relative energy
45. ntervals dSRC Sdx 5 m A short sampling interval of 0 25 ms dt 0 25 ms was used because refraction analysis was also planned A fairly short recording time of 1 sec T 1 sec was used to avoid inclusion of fairly strong ambient noise as much as possible To suppress the ambient traffic noise three impacts with about 2 sec interval were applied at each shot location to save one field record of three vertical stack Active Survey MAS Sure Tr Figure 2 3 Figure 2 4 Step 1 Formatting Go to Utility gt Format and then select all 10 records 1000 dat 1009 dat Specify output file name Active dat and then click Run Format button Step 2 Field Setup Go to Utility gt Field Setup and then open the formatted data Active dat Make sure Active button is selected in survey type dialog box Figure 2 4 A graphical dialog box will appear Figure 2 5 Type in station numbers for the first two traces of the field record displayed in the background Stations numbers are arbitrary fictitious numbers used as reference surface coordinates Assign 1005 and 1006 for the first two receivers in the graphics window Figure 2 5 Type in 5 0 and 1 0 for the source offset x and receiver spacing dx respectively Choose meter for the distance unit Make sure Source Location has been correctly detected by the program If not override it manually Then select Source R
46. o POS that Swtwemaneaansive is updated whenever Vs is updated on each iteration a ny tt E Previously it was fixed to POS Update depth Z EE Payne model with each curve option in Initial Vs Layer tab will update the thickness depth part of the layer model according to the wavelength range aene AmnAna determined from each curve being semna a inverted Previously it was fixed to the average memme eres value determined from all the input curves 15 jie Checking Excel File x1 option in Output Files Sse tab will make an additional output file with XL ews eer extension where shear velocities Vs s are displayed along each column representing a specific Figure 6 1 surface location This option is available only in the case of a fixed depth model second and third options in Initial Vs Layer tab 31 6 2 Inversion of Dispersion Image OT Record Go to Analysis gt Inversion and then select the file a TITT type of overtone record dat at the bottom of the commence open file dialog Figure 6 2 Then select an overtone Semana a Eta file generated from a seismic data set by following the Sioana procedure explained in Section 5 1 A separate window will show up where the first overtone record in the file i displayed and all the inversion controls are displayed in a separate panel on the right Figure 6 3 The
47. ose two steps Steps 4 and 5 explained below and 2 inversion of OT records without extraction of dispersion curves explained in section 6 2 Step 4 Extraction of Dispersion Curves from Overtone Image See section 5 2 Step 5 Inversion for 2 D Vs Profile See section 6 1 Chapter 3 Passive Remote MASW A passive surface wave survey with a 2 D receiver array will give the most accurate evaluation of dispersion trend Park and Miller 2006 This mode of survey however requires a wide area for the 2 D array which is to be deployed some distance away remote from points of surface wave generation to meet the plane wave propagation assumption In the case of a roadside survey this distance can be a fraction e g 20 of the dimension D of the receiver array Procedures in data acquisition and processing are explained below 3 1 Receiver Array Any type of 2 D array of fairly symmetric shape can be used Figure 3 1 An array of significant asymmetric shape for example an elliptical or elongated rectangular shape is not recommended due to bias toward a specific direction of incoming surface waves that do not necessarily coincide with actual direction of major surface wave energy Common types may include circular cross square triangular random etc arrays Figure 3 1 A detailed study comparing each different type of array in its effect on the dispersion analysis has not been can FaN 05 i psoeeberny o
48. r 4 for passive roadside MASW methods See Chapter 5 See Chapter 6 Figure 1 2 Table 1 1 Summary of Sample Data Parameters Survey Type Active Passive Remote Passive Remote Passive Roadside MASW MASW MASW MASW File Name s 1000 da Passive Cross dai Passive Circular dai 4000 dar 1009 dat 009 dat Folder T activer PassiveRemoiel __ PassiveRemote PassiveRoadside Survey TD Vs Profiling TD Vs Profiling TD Vs Profiling ED Vs Profiling Purpose Data Format SEGT KOS KOS SE Acquisition 24 channel AR channel 24 channel 48 channel Source Tb Hammer Traffic Traffic Tib Hammer Traffic Receivers 45 Hz 45Hz 45Hz 45Hz land streamer Geophones spike coupling spike coupling spike coupling with 30 takeouts Receiver Linear Cross y Circular Tinear Array ol along rol along Array Bm Tsm Tsm 33m Dimension 0 Receiver Tir im Tm TIm Spacing dx Source Offset Sm NK NK am bs Receiver Sem 7 T CCEE Array Move Sampling 025ms Tins Tas Tas Interval at Recording Tsee Tse Tas Tae Time 7 Record 100 1009 3000 3005 3000 3009 1000 4009 Numbers Chapter2 Active MASW Survey This is the most common type of MASW survey that can produce a 2 D Vs profile an example of which is displayed in Figure 2 1 Maximum depth of investigation Zma that can be achieved i
49. s all you need to do at this stage will be simply to launch the wavefield Figure 5 2 transformation process by clicking Start Processing button After the process is finished you can now move to the next step of either Step 2 Extraction of Dispersion Curves from OT Image section 5 2 or Inversion of Dispersion Image section 6 2 Fk ot Contariraten Hater Hodes igh Stack Same Mid Station OT s option Figure 5 1 will if checked vertically stack those overtone OT records of the same mid station numbers and then the stacked record will be saved This option is useful when multiple records were acquired at the same location and saved separately with different record numbers e g 5001 5010 On importing the input file the program scans the input records to see if it contains repeated records and checks the option if detected Append Output option will if checked allow the output to be appended to an existing file In this case it is critical to ensure the same ranges and intervals in frequency and phase velocity between the current processing and the processing applied to the existing file to be appended Processing parameters a 7 awe Em oie Gale e influencing the OT data rresia aut E quality can be accessed by as clicking Show Parameters button in the dialog box Figure 5 1 These parameters are grouped into four tabbed pages Frequency and
50. s encoded the next step is to process for dispersion information This process consists of two steps 1 generation of dispersion image called overtone data set and 2 extraction of dispersion curves from it 5 1 Step 1 Processing for Overtone OT Image Data Go to Analysis in the main menu and then Dispersion to open a field geometry encoded seismic file dat Then a dialog box will appear Figure 5 1 In the case of active data results of pre scanning input data will be displayed in a separate box Figure 5 2 It will show qualitative evaluation of data on possible ranges in surface wave velocities frequencies and on p Cire Bini CEEE Sea eer ome ich See sens Sem Reet tents ee ial Om pale pales Vat al a a a a mam temal vaj pe Gries iesea EEE Donasan pines ee roc ern it Ser L r L l J pe a xaa sa j xem vo aT Boemiae Minime EEEE Bemire mse CRE ramet fan nt remark om xen ga xem pr Figure 5 1 the relative degree of higher mode domination It will be however a rough evaluation and by no means a complete or definitive one The OT generator dialog box Figure 5 1 will pussy ra opus 40 80 lms show input and output information with output file name assigned by the program Because most processing parameters will usually have been set properly by the program from the pre scanning proces
51. s the one included in previous versions of SurfSeis On the other hand the latter type is a Monte Carlo method that randomly searches for a layer model whose dispersion curves best match those trends in the overtone image This type can therefore perform a mul modal inversion and all the parameters Vs Vp thickness etc of five layer earth model can be manually manipulated Although the former type has been explained in the previous version v 1 5 of the manual Chapter 4 it is briefly explained again here pine Bn ja aie 6 1 Inversion of Dispersion Curve Go to Analysis Inversion and select dispersion 500e yee curve files previously extracted and saved by Lovaas leis following procedures Steps 1 and 2 described in ee Chapter 5 Once the files are imported the program will sort them by an increasing order of mid station numbers encoded in each file Then click the Run syounmaawme SIE button to launch the inversion process with all default parameters of inversion set by the program Description of controllable parameters at this stage can be found in the previous version of the manual Sep aemccayoncneges 2 section 4 4 However changes made into this errant version of SurfSeis are described below Bev nana iasa Update with Vs option in Iteration tab of the eA control dialog box Figure 6 1 can specify either P velocity Vp default or Poisson s rati
52. s usually in 10 30m range However it can vary with different sites and different types of active sources used Field procedures and data processing steps are briefly explained below Some of the field parameters for example source offset x and receiver spacing dx are described based on the most recent research results and therefore may be different from those previously reported Description of data processing steps is presented by using a sample field data set stored in SurfSeis20 SampleData folder Recording parameters are listed in Table L1 The description is focused on those new features with this particular version 2 0 of SurfSeis and it is recommended to refer to previous v 1 5 manual and README files for the description of all those features not explained here Surface waves are best generated over a flat ground at least within one receiver spread length D Figure 2 2 Then overall topographic variation within an entire survey line should not matter However any surface relief whose dimension is greater than say 10 of D will cause a significant hindrance to the surface wave generation Figure 2 2 Active Tosi FioldSolup ActiwoO Vs GRD vast wn E ao sa om s 5 E o Evo oF Eis Z 8 163 a Figure 2 1 O 0 O ai Figure 2 2 2 1 Data Acquisition The following sections describe most of the parameters related to data acquisition They are the ones most commonly use
53. than all four will make the transformation focus into certain directions This can often enhance the image resolution obtained from the transformation as far as those quadrants are properly selected For example if the survey took place on the west side of a road running south north S N where major portion of surface waves were generated specifying only the two quadrants of NE and SE will be a good choice Also using a smaller number of quadrants will save computation time Angle Increment specifies interval of azimuth scanning and can sometimes influence the image resolution depending on the relative location of possible multiple points of surface wave generation A smaller interval will increase computation time The azimuth information Figure 5 2 of the surface waves will be saved with a file name of Azimuth dat if the option is checked accordingly In the case of passive roadside data there will be an additional parameter to specify the offline distance between the linear receiver array and center of the road from which the major energy of surface waves came This value can be precise only within a certain fraction such as within 50 Zero value 0 will make the transformation be based on the assumption that all the surface waves recorded came in perfect inline with respect to the array without any azimuthal deviation This will therefore make the transformation skip the azimuthal scanning process and the comp
54. the shortest wavelength Amin and therefore the shallowest resolvable depth of investigation Zain dx Amin Zmin 42 4 2 Data Acquisition The following explanation covers most of parameters related to data acquisition These parameters are the ones most commonly used at KGS and by no means represent a required set of values Slight variation in any parameter can always be expected 16 Recording Parameters Please note that the maximum number of samples per trace that can be processed with SurfSei limited to 32000 which is more than enough in most cases as explained below Sampling nterval of 4 ms dt 4 ms and total recording time of 30 sec T 30 sec are most commonly used at KGS when surveys are performed inside the city of Lawrence Total recording time T s determined in such a way that there is at least one occurrence of passive surface wave generation during recording Therefore it can be reduced or increased depending on local situations related to the surface wave generation In case of surveys near roads for example there should be a vehicle passing near the survey area at least once during recording The longer T is not always better This is because the chance of recording surface waves generated at different locations on the road increases as well and it will in general degrade the data processing resolution unless those locations are well apart in azimuth for example 90 or more If the main source point
55. un Format button Step 2 Splitting Data into Active and Passive Sets Because an active impact was applied at the beginning of the 120 sec recording the early portion of data contains active surface waves that can be processed by the normal active processing procedure explained in 2 2 whereas the later portion contains the passive surface waves As processing schemes are different for active and passive cases they have to be separated to avoid adverse influence on each other Usually the first 2 sec portion is enough to take most of the active surface waves In addition because of 48 channel acquisition was used along with 30 receiver land streamer eighteen 18 traces in each record have to be discarded These procedures are explained below Go to Display Seismic and then open the file formatted in the previous step e g Roadside dat Display first few seconds portion of data by using the zoom button in the top tool panel to estimate possible record length for the active part 5 Figure 4 2 Then Cut Append Records button in the Figure 4 2 18 tool panel Figure 4 2 A dialog box will show up Check All Records box in Record tab and then choose Trace tab to type in I and 30 for pra beginning and ending traces to cut Figure 4 3 The aula choose Time tab to type in 0 and 2000 for beginning and ending times to cut in milliseconds ee Click Save O
56. utation can proceed at a significantly faster speed to generate a fairly clean image in most cases However the dispersion trend will be overestimated often by 30 or more see Park and Miller 2006 It is recommended therefore to use this option zero offline offset only as a reconnaissance tool in the field Contrast This controls relative emphasis of one dominant mode of dispersion in comparison to other modes possibly existing together The higher contrast will make one dominant mode at each frequency prominent whereas the smaller one will enhance other modes if they exist as well Records Specific record s rather than all can be selected for the image data generation 24 Once overtone data set is generated you can move either to 1 extraction of dispersion curves explained in the next section 5 2 or directly to 2 overtone image based Monte Carlo inversion explained in 6 2 to come up with a Vs profile The extracted dispersion curves will be used for the linearized gradient based inversion to come up with a Vs profile explained in section 6 1 Algorithm This option is available only for the active data Normal algorithm accounts for the relative phase relationship between seismic data from different receiver locations and this is the most reliable method of dispersion imaging with the least number of computational artifacts The Advanced algorithm can achieve a higher resolution in the constructed dispers
57. utput As button at the bottom to typein renauysus output file name e g Roadside Active dat Click me OK in the dialog box to launch the cutting process neve Repeat the same procedure with 2000 and 120000 for the cutting time range of the passive data set to be sons wmomo r saved with another unique file name e g Roadside SIE Passive dat The Record s Move edit box in Record tab indicates the number of records repeatedly saved atthe same location before the source receivers S 1 Ime configuration SRC was moved to the next location This option will take effect only when the Stack a L a E Vertically before Output option is checked In that Ries case these repeated records will be stacked together Sri before written into the output fil Step 3 Field Setup ae Go to Utility gt Field Setup and then open the active data set first e g Roadside Active dat Make sure e Active button is selected in the survey type dialog box A graphical dialog box will appear Figure 44 Type in station numbers e g 400 and 4001 for the first two traces of the field record displayed in the background Stations numbers are arbitrary fictitious numbers used as reference surface coordinates However station numbers should match those that will be used in the passive data set and therefore need to be remembered Type in 4 8 and
58. window type is basically identical to the one displayed during the Figure 6 2 step to extract dispersion curves section 5 2 only with the inversion panel added Controls in this panel are explained in a grouping pages Modeling Inversion and Output Figure 6 3 ese paama a tw three tabbed _ _ _ _ _ _ _ oo_ z EPEE stil EN vote ey S smn entrees aon S TETS mm hie e p ap ae ho a aa ir mapa f o ar aa fo 2 x E mien e aseetan aena nme ni Figure 6 3 Modeling All parameters related to the layered earth model are grouped here in another set of tabbed pages thickness H shear velocity Vs P velocity Vp and Poisson s ratio POS Figure 6 4 Number of layers is limited to five 5 at most and two at least and can be changed in of layer edit box Figure 6 3 The last layer always represents the layer of infinite thickness the half space All these parameters are used to generated theoretical dispersion curves through the forward modeling scheme by Schwab and Knopoft 1972 Dispersion curve parameters are 32 grouped in a separate pje uuiy nef page of Bom Re me mee where frequency range fF tim me jimenl i f mt pom and interval can be emer PS stats BET specified for multiple up to four modes MO M1 M2 and M3 Figure 6 4 Wavelength depend
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