1. Introduction
Contents
1. Synthetic data generated by SU Real shot gathers from the Oz Yilmaz collection at the Colorado School of Mines ftp ftp cwp mines edu pub data and Real 2 D marine lines provided courtesy of Prof Greg Moore of the University of Hawaii the Nankai data set and the Taiwan data set o The University of Texas the University of Tulsa and the University of Tokyo collected the Nankai data The U S National Science Foundation and the government of Japan funded acquisition of the Nankai data o The University of Hawaii San Jose State University and National Taiwan University collected the Taiwan data The U S National Science Foundation and the National Science Council of Taiwan funded acquisition of the Taiwan data Chapters 1 3 introduce the Unix system and Seismic Un x Chapters 4 5 build three simple models complexity slowly increases and acquire a 2 D line over each model These chapters may be skipped if you are only interested in processing Chapters 6 9 build a model based on the previous three acquire a 2 D line over that model and process the line through migration Chapters 10 11 start with a real 2 D seismic line of shot gathers Nankai and process it through migration Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction Chapters 12 13 and 15 16 start with a real 2 D line of shot gathers Taiwan and pro2. the data to the next program suxwigb the X window display program displays the seismic data on your screen as wiggle traces e The amp needs a special explanation Read the next section ee fe SE PoP xwigb P T TTA ETAT HTH Way H I LITTKLIITITTII IT HTT l ITP HVAT TINT LI Mt HUTTE 233333111 ER NII HITTI TITTI KIIT gt H 11I I1 1 pi TE R M HT HITTI I H LI Figure 1 4 The output of your first SU command The upper left corner shows 0 200719 8 05814 because we clicked the middle mouse button at approximately 0 200 ms time the vertical axis is time and on the eighth trace from the left the horizontal axis is trace number 1 9 Computer Note 5 Background amp and Foreground Processes 1 9 1 Background Processes In technical language using amp ampersand at the end of a command runs spawns the process in the background In simple terms using amp does not lock your cursor Since your cursor is not locked frozen when you use amp at the end of a command you can use the same x term to do other things like submit other processes For example the following command starts the Netscape web browser as a background process netscape amp To enter
3. 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction 1 13 1 Computer Note 6 No Spaces around the Egual Sign Do not use spaces before or after the egual sign 1 14 Other Help Facilities in Seismic Un x Various help facilities are described in The New SU User s Manual by John W Stockwell Jr amp Jack K Cohen Version 3 2 August 2002 This Manual is available at the CWP Seismic Un x web site In addition to the self documentation described in Section 1 11 other help facilities include e suhelp lists all the available programs suname lists all programs and libraries with a short description of them sudoc followed by the program name gives documentation of the program This can work even when there is no selfdoc for the program sufind followed by a string searches in all self documentation for this string e sukeyword lists keys used for headers e demos is a directory in the SU installation that contains useful scripts 310 398 A Ie1g1 dNYy ye asc JO SULIDT das JYSIIAdOI 10 ISUN HAS 0 199 gNnS UonNnaInsIPoa PO TSLI TEI OI H TT 1O popeojumogd
4. directory is that as I go to deeper subdirectories the prompt becomes longer Figure 1 3 I am willing to pay this price for the information that I gain Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction home fore1l gt H Figure 1 2 My new prompt shows the current directory I also changed to gt Seismic Un x 3 home forel seismicx demos Filtering sufilter gt J Figure 1 3 A prompt with a long path name To change your C shell prompt edit your home directory s shell resource file The file cshrc is the resource file for the C shell Yes the file name starts with a period Use any editor you like to add the following lines to your cshrc file Note We use only Unix based text editors to write and edit shell scripts and resource files Many personal computer editors insert hidden format codes that might be wrongly interpreted by the Unix operating system Make prompt contain pwd lias setprompt set prompt S cwd gt lias cd cd amp amp setprompt lias pushd pushd amp amp setprompt lias popd popd amp amp setprompt setprompt moo o The first line is a comment When the first character is the entire line is ignored After you save your changes when you open a new x term window the system will read the resource file and use those instructions in th
5. Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction 1 Introduction 1 1 The Goal of this Primer Our objective is to introduce you to the fundamentals of seismic data processing with a learn by doing approach We do this with Seismic Un x SU a free software package maintained and distributed by the Center for Wave Phenomena CWP at the Colorado School of Mines CSM At the outset we want to express our gratitude to John Stockwell of the CWP for his expert counsel SU runs on several operating systems including Unix Microsoft Windows and Apple Macintosh However we discuss SU only on Unix Detailed discussion of wave propagation convolution cross and auto correlation Fourier transforms semblance and migration are too advanced for this Primer Instead we suggest you refer to other publications of the Society of Exploration Geophysicists such as Digital Processing of Geophysical Data A Review by Roy O Lindseth and one of the two books by Ozdogan Yilmaz Seismic Data Processing 1987 and Seismic Data Analysis 2001 Our goal is to give you the experience and tools to continue exploring the concepts of seismic data processing on your own 1 2 The Outline of this Primer This Primer covers all processing steps necessary to produce a time migrated section from a 2 D seismic line We use three sources of input data
6. box with the left mouse button The left image shows the mouse dragging the box The right image shows the zoomed image To return to the original view click the left mouse button in the window 1 11 The Demos Directory The demos directory is a standard part of the SU installation If you don t know where yours is ask someone It is full of easy to use demonstrations of many seismic data processing programs Once you are in the demos directory repeatedly use cd to move around Use Is and pwd frequently to see where you are Notice the many README files The README files tell how to use the demonstrations in each directory You can write README files to your screen by typing either of the following commands cat README more README If you use the second command you can advance the text that appears on your screen by pressing the spacebar to move to the next page Pressing Enter or Return scrolls the display one line Exploring executing the demonstrations is an easy way to see seismic data processing 1 12 Self Documentation in Seismic Un x To display documentation for programs like suplane or suxwigb enter the name of the program without arguments Without arguments means you enter only the name of an SU program For example enter suplane Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction SU interprets this to mean you want informa
7. cess it through migration Chapter 14 uses real shot gathers from the Oz Yilmaz collection to demonstrate f k filtering and deconvolution We introduce the major processing steps in the following chapters Build a model Chapter 4 Acguire seismic data Chapter 5 Amplitude correction Chapter 10 Freguency 1 D filtering Chapter 10 Freguency wavenumber f k filtering Chapter 14 Deconvolution Chapter 14 Sort from shot gathers to CMP gathers Chapter 7 Velocity analysis Chapter 7 Normal moveout correction NMO Chapter 8 Stack Chapter 8 Migration Chapter 9 Scripts are included for each process A detailed description of these scripts is the heart of this Primer Experience with the Unix operating system is helpful but not necessary Chapter 2 introduces Unix commands and SU scripts 1 3 A Bit about Seismic Un x Seismic Un x Cohen amp Stockwell 2002 is a free software package for seismic data processing SU is maintained and regularly updated by the Center for Wave Phenomena CWP at the Colorado School of Mines CSM The SU home page at the CWP is http www cwp mines edu cwpcodes You can download SU from the CWP ftp server and install it on almost any Unix system The source code is also included making it possible for you to adjust and expand SU The CWP web site also contains links to other useful web sites Please read the legal statement that accompanies SU For your conve
8. e new x term window If you want to use cshrc changes in your current window enter source cshrc 1 8 Your First Seismic Un x Instruction Before you can run Seismic Un x you must be sure your SU commands will be interpreted by the Unix operating system This means SU must be in your path Your system administrator may have made SU part of your login path or you may have to enter a command first The approach we use at Michigan Tech is described in Appendix B Let s run a simple program to test that you and your SU environment are working together Enter type the following then press the Enter or the Return key suplane suxwigb amp You should get a new window with a picture of some synthetic seismic data on your screen Figure 1 4 If you do not ask someone for help The style of the above command is program pipe output data to next program program amp sel Kz The pipe I directs data from one process to another Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction You can regain the Unix prompt in your SeismicX window by pressing the return key if you supplied amp at the end of the command You can close the graphics window by using the Unix Close command the top left button Let s discuss the details of the above command suplane creates seismic data the pipe the vertical bar directs sends
9. ng a line command enter kill 9 9828 The flag 9 tells kill that you are serious about killing process 9828 1 9 2 Foreground Processes When you start a process and don t use amp the new process uses the current x term the process runs in the foreground which locks the cursor For example the following command starts the Netscape web browser as a foreground process netscape To continue working when the cursor is locked you must either kill the process that you just started or you must open a new x term To kill a foreground process in an x term window 1 click the window to make it active 2 hold down the Control key and briefly press the c key press Control c This kills the process Because the process dies the browser window also closes 1 10 Zoom the xwigb Window You can zoom the image in the xwigb window Put the cursor somewhere in the xwigb window press and hold down the left mouse button drag the mouse until the box encloses the area you want enlarged then let go of the button You can zoom repeatedly Notice that time numbers and trace numbers correspond to the zoomed data Click once in the window to return to the original view Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction H DUETIN Pa Figure 1 6 Zoom an xwigb window by dragging a
10. nience we make this available as our Appendix A SU is easy to use because it does not require extensive programming knowledge only basic Unix commands for file management pipes and shell redirection see Chapter 2 Although SU can be run from the command line the most efficient way to use SU is through shell scripts Shell scripts let us combine several processing programs into one job similar to commercial seismic processing packages We first describe Shell scripts in Chapter 2 1 4 Computer Note 1 Enter When we tell you to enter something on the computer we want you to type the instruction then press the Enter or the Return key Pressing Enter or Return tells the computer to execute the instruction Merely typing an instruction on a line does not execute the instruction Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction 1 5 Computer Note 2 Your Shell When you enter a command you are interacting with the Unix shell There are several Unix shells the Bourne shell the C shell the Korn shell the Bourne Again shell BASF and others All example scripts in this Primer use the Bourne shell most of the Computer Notes refer to the C shell 1 6 Computer Note 3 Changing Directories 1 Open an x term window and enter pwd on some computers you have to use cwd to see the directory in which you are now working Enter 1s t
11. o see a listing of the files and subdirectories in that directory 3 If you have a subdirectory for example work enter cd work to change to that subdirectory then enter 1s to see a listing within it 4 When you want to move up one level of directory enter cd Yes that is cd space dot dot 5 If you enter cd by itself you will go to your home directory If you enter cd cd space dot you will not go anywhere because the single dot period is a reference to your current directory The single dot can be useful Suppose there is a system calculator called xcalc and suppose you wrote your own calculator program that is also called xcalc If you enter xcalc the system version might start instead of yours To run your version instead of the system version go to the directory that contains your version then enter xcalc The dot slash tells the system to look in the current directory for the program 1 7 Computer Note 4 Cursor Prompt Usually the default computer prompt does not give much information For example Figure 1 1 shows the default prompt when I Forel open a new x term window latspot lt 1 H Figure 1 1 Forel s default x term prompt The prompt of Figure 1 1 shows the name of the machine that I am on and the number of the command 1 that I am about to enter I think a more useful prompt is one that tells me which directory I am in Figure 1 2 A disadvantage of a prompt that shows the current
12. other commands after this one press Enter again to regain a prompt then enter your next command Downloaded 01 21 14 to 132 178 2 64 Redistribution subject to SEG license or copyright see Terms of Use at http library seg org Introduction While a process is running in the background you might need to cancel kill it You can do this using a Unix utility called top 1 In an x term window enter top 2 The x term window now shows your most active processes Figure 1 5 and the cursor is now in the upper left of the top display shown as the red box in Figure 1 5 load averages 0 01 0 03 0 05 73 processes 72 sleeping 1 on cpu CPU states 97 2 idle 0 4 user 2 4 kernel 0 0 jiowait 0 0 swap Memory 384M real 107M free 131M swap in use 2157M swap free PID USERNAME THR PRI NICE SIZE RES STATE TIME CPU COMMAND 8731 forel 11 48 0 18M 16M sleep 1 16 0 37 dtmail 9811 forel 4 59 0 19M 14M sleep 0 01 0 19 sdtimage 6942 root 1 22 59 0 144M 101M sleep 5 26 0 15 Xsun 9809 forel 1 49 O 2240K 1280K cpu 0 00 0 14 top 9828 forel 122 25 5 26M 18M sleep 0 04 0 00 netscape Figure 1 5 Screen capture of Forel s top processes 3 The left column PID identifies process netscape the Netscape web browser as 9828 To kill this process enter k 9828 4 To exit top enter g for quit Note You can use top to learn the process ID PID then kill the process using a line command To kill the Netscape process described above usi
13. tion about suplane so SU prints the program help selfdoc file to the screen Below are the first several lines of the suplane selfdoc file SUPLANE create common offset data file with up to 3 planes suplane optional parameters gt stdout Optional Parameters npl 3 number of planes nt 64 number of time samples ntr 32 number of traces taper 0 no end of plane taper 1 taper planes to zero at the end offset 400 offset dt 0 004 time sample interval in seconds You see that the name stands for create common offset data file with up to 3 planes Many SU program names start with su You also see the default values values used when the user does not supply a value of various parameters such as the number of planes npl 3 the number of time samples per trace nt 64 and the time sample interval dt 4 ms Using default values each trace is 256 ms long 1 13 Your Second Seismic Un x Instruction Let s change the command given earlier in Section 1 8 Enter suplane npl 2 dt 0 008 suxwigb amp By supplying values for npl and dt you overwrite replace suplane s default values Your output pictured below has only two planes and each trace is 512 ms long Figure 1 7 The suplane command with two defaults overwritten number of planes 2 and time interval 0 008 seconds Downloaded 01 21 14 to 132 178 2
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