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Data Analysis for Refraction Tomography


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  • 1. 12.12.2007Data Analysis for Refraction Tomography Data Conversion Killing Signal Picking Approaches SeisOptPicker Model Geometry y Senior Project-Geop402 Dr.Ali o.Oncel First Break Picking Module 4 copy of SeisOptPicker is uploaded to PC in Computer Lab of ESD. 1
  • 2. 12.12.2007 Data ConversionMAKE SURE you name the converted SEG2 files sequentially. That is, name themP1_S01, P1_S02 etc (see above showed SEG-2 files). If you do this, you can be surethat the SU file will also show the shots in sequence. Otherwise you will see shot 1 firstthen shot10 11, and so on 2
  • 3. 12.12.2007 Some Pitfalls and Solution • Differences in the Recording Length can cause such ki d of diff h kind f differences. Th Thus, one is asked to checked. • Recorded Length for first data is 2 ms while others have a shorter record length, which is 1.5 ms. • Solution: Ignore those data having different length and later combine. Header EditThis year, we have recorded 96 traces with 3D geophones, kept 32 of those and deletedother horizontal components based traces (64). Then, Header Edit is required to fixHeader Size to number of data. This is an example for converted data from SEG2 toSU. 3
  • 4. 12.12.2007 Header Edit TRACF Enter values as E t l 1,2,3,4,5,…….32Senior Project-Geop402 Data Conversion Killing Signal Picking Approaches SeisOptPicker Model G M d l Geometry t 4
  • 5. 12.12.2007Signal Killing on DISPLAY by SEISOPTPIC PERMANENT Killing by INTERPEX 5
  • 6. 12.12.2007 6
  • 7. 12.12.2007S1 Deleted. Now, you want to delete S2 tokeep V1S2 Deleted. You have only traces of V1 7
  • 8. 12.12.2007Compare Traces: How it worked well?Selected Traces by INTERPEX by componentTraces by TSPRO by one to one deleting signals. CONVERT FILE to SEG-2From what I have experienced, If click EXPORT SEG2, it may notbe read by other programs in case one modified the data 8
  • 9. 12.12.2007Senior Project-Geop402 Data Conversion Killing Signal Picking Approaches SeisOptPicker Model Geometry 9
  • 10. 12.12.2007 Seismic Record First b k Fi break First departure First Kick TimeSource: Lie, M., 2000, , Master Thesis, University of Sydney. Corrections on Seismic Record No DC Shift DC Shift Well-known seismic software has such kind of tool to make a correction. 10
  • 11. 12.12.2007 Manually Picking Consistency is very important for manually picking. Then, it is better to select one model of picked seismic waves.Source: Lie, M., 2000, Seismic Applications of Interactive Computational Methods, Master Thesis, University of Sydney. One Approach for Manually Picking Model Signal is assigned as a Reference Signal and kept as a fixed. Selected signal There is no matching since time delay due to changes in distance makes a changes in waveform overlapping. Overlapping signal Signals are overlapped and same location as picked on reference signal is aimed to pick. The similarity between two signals are given by value of ratio as As/Ar. One Approach for Manually Picking Signal Such option you can find under the program of TSPRO. Visit to class page. 11
  • 12. 12.12.2007 Automated Picking MethodsI suggest you to read a couple of papers for pickingFirst Arrivals since it is an important part of datapreparation. A couple of papers you can easily find: 12
  • 13. 12.12.2007 13
  • 14. 12.12.2007Automated Picking Methods by Interpex Easy to download from Class Page 14
  • 15. 12.12.2007Truncate Traces: Enlarging Signal I have cut the signals for time larger than 125 Milliseconds since First Arrivals were appeared before. Trace Plotting Parameters Automated Gain Control is nice option to strength the signal which can be easily detected. 15
  • 16. 12.12.2007Picked ExamplesPicked Examples 16
  • 17. 12.12.2007 Picked ExamplesPicking Experiences: Clean Record 70 60 Time (ms) 50 40 30 T 20 10 0 0 5 10 15 20 25 30 35 60 50 40 s) Time (ms 30 20 10 0 0 5 10 15 20 25 30 35The clear data makes picking arrivals easy and observed slight differences on pickeddata made by two different person. 17
  • 18. 12.12.2007 Picking Experiences: Noisy Record 100 90 80 Tim (ms) 70 60 50 me 40 30 20 10 0 0 5 10 15 20 25 30 35 Distance (meter) 90 80 s) 70 60 Time (ms 50 40 30 20 10 0 0 5 10 15 20 25 30 35The noisy data makes picking arrivals difficult and observed slight differences onpicked data made by two different person.Picked Examples on Good Records 70 70 60 60 50 50 Time (ms) Time (ms) 40 40 30 30 20 20 10 10 0 0 0 10 20 30 40 0 10 20 30 40 Distance (meter) Distance (meter) It is an average data makes picking arrivals easier than noisy data. 18
  • 19. 12.12.2007 Concluded Remarks• It seems that Hatherly Picking Technique makes a good job for initial picking but it is better to check one to one for each signal.• Filtering is difficult for areas of higher noise since following filtering data is out, one faces up another noise of different frequencies.• Traces Plotting Parameter for example AGC Parameter, AGC, provides strength traces• Noisy data requires a significant time to find true picked values of arrival times. Senior Project-Geop402 Data Conversion Killing Signal Picking Approaches SeisOptPicker Model Geometry 19
  • 20. 12.12.2007Read Converted Data 20
  • 21. 12.12.2007 RECORD 1 Click here to PS_01 see next recordRECORD 2 Traces are also consecutively PS_02 shown. 21
  • 22. 12.12.2007RECORD 13 Traces are also consecutively PS_13 shown. Factors Affecting Arrival Times2006-2007: We had records on material with relatively fastvelocities through Profile1 which is only about 10m. So thearrival times appeared to be very small Unfortunately the small. Unfortunately,resolution of the traces became poor (lower frequency).Because sample interval of seismic interval was smaller than0.25 milliseconds, due to old instrument,.2007-2008: We made seismic survey with state of artseismometer which provided high quality of records with0.125 milliseconds. Now, we could see better resolution ofthese picks. 22
  • 23. 12.12.2007 PICKING DATA Zoomed in Window time display Type 50 ms Set trace size=20 Window time display No equalization Clip amplitudeI used the tool "zoomed in" to the top part of the traces for picking You do thisby selecting "window time display" under the "Display option" menu. Type in 50(for 50 milliseconds) and the top 50 milliseconds will be shown. You can see thefirst-break clearer now. I also set trace size to 20 (top left scroll bar all the way to the right). Iselected "No equalization" under Display Option->Trace Equalization andSelected "Clip Amplitude" also. Saving Pick File Next step is the enter geometry. After picking all the traces, make sure to click "Save FBP" button. This will turn the red picks to blue color. I tried auto picking but gave up since it doesnt work well for this data. I picked each trace manually the best I could. You will notice all the picks are almost same arrival time – Once again so to say, it is a combination of short distances and the sampling rate used not being high enough. 23
  • 24. 12.12.2007Senior Project-Geop402 Data Conversion Killing Signal Picking Approaches SeisOptPicker Model Geometry 24
  • 25. 12.12.2007 S_13 S_01 9.9 M S_12 S_11 S_10 S_09 S_08 S_07 S_06 S_05 S_04 S_03 S_02 G_1 G_2 G_3 G_4 G_5 G_6 G_7 G_8 G_9 G-10 G_11 G_12 Shots Data Distance (m) Shot X and Firs Receiver t S_1 P1_01 10.35 4.5 m S_2 P1_02 9.45 S_3 P1_03 8.55 S_4 P1_04 7.65 S_5 P1_05 6.75 S_6 P1_06 5.85 S_7 P1_07 4.95 S_8 P1_08 4.05 S_9 P1_09 3.15 S_10 P1_10 2.25 0.0m S_11 P1_11 1.35 9.9m S_12 S 12 P1_12 P1 12 0.45 0 45 S_13 P1_13 -0.45First Receiver X = 0.0Shot X = 10.35 Receiver Spacing= 0.9 m Shot Spacing= -0.9 mS= Shoot locationG= Geophone location Shot 13 Profile Geometry Shot 1 "Record SHot" before going to "Next Make sure First Receiver X = 0.0 Record”. And, make sure the receiver spacing is changed to 0.9 and check the Shot X for “Shot 1” is 10.35 coordinates in the row below. Shot X for “Shot 13” is -0.45 Things seems working on the Model Geometry regarding the Off-profile Shot Locations Now, check it again by touching “?”, then exit . 25
  • 26. 12.12.2007 Save and ExportFollowing the tasks of entering the data for profile geometry and picking the data of firstarrival, then it is time to save and export the file for SEIS-OPT for constructing 2Dmodel of refraction velocity. Data Control Show files The data is ready for a final check before saving Check it clearly till you are satisfied saving. with the entered data on their correctness since the present data is input for modeling software of refraction velocity (Seis-OPT). Then, Save Pick Files if nothing seems wrong. That is a final reminder for data. If it is true, click “Save SeisOptPick files” and then “Show files”. 26
  • 27. 12.12.2007 S= Display Shot F= Display First break Coordinates time (s) G= Display Receiver X and ZCheck the file for each of above those inputs, the Save them individually under the FILE.Then, you are suggested to open saved files one more time from where the files aresaved. If files on data are saved truly, now it is time to work with the other program(Seis-OPT) for modeling 2D velocity. Problem: Missing Data 27
  • 28. 12.12.2007 SuggestionsWhat you do is click "Yes" in the dialog box that th t asks "Fi ld number missing correct k "Field b i i t now". Then you enter "1" when it asks enter first field id number. Click ok. The first time you will see empty box in the export window as in slide 2. Do the export again and now you should see the values 28
  • 29. 12.12.2007Further Reading: Manual 29