Open Data/Open Source: Seismic Unix scripts to process a 2D land line

Setting up and reading the data documentation

Download Madagascar and you should have all files to process line 31-81 in the directory: $RSFSRC/book/data/alaska/line31-81.

Change into this directory. This paper lists commands and the SConstruct file contains the rules that translate the commands into SU tasks to process the data.

An alternative to installing Madagascar is to go to the website http://dl.dropbox.com/u/37269048/open_lib_demo_2011.tar.gz

This will download a tar file that you can install. On my system I do this with the commands:

cd
mv Downloads/rsf-alaska.tar.gz .
tar xvzf rsf-alaska.tar.gz

You can run the script from the tar file:

./prevstack.job

The scons will download the file 31_81_IM.JPG from the Internet and display it using open office draw (oodraw). The tar file supplies the files so the scripts skip the download. ./prevstack.job just displays the file using oodraw. There used to be a higher resolution image of the stack display, the file S609.TIF. This file is no longer available on the USGS Internet site. I was able to view this file in OpenOffice.org draw and zoom to read the side label that describes the acquisition and processing parameters.

The data was acquired 96 trace, 12 fold with a dynamite source. The shotpoint interval is 440 ft and the receiver interval is 110 ft. The average shot depth is 75 ft. The elevation plot on the section header shows the elevation is about 200 ft and there is little variation.

The processing applied by GSI in 1981 was:

1. Edit and true amplitude recovery
2. Spherical divergence and exponentiation (alpha - 4.5 db/s, initial time - 0 s, final time - 4.5 s)
3. Velocity filtering dip range -12 to 4 ms/trace
4. Designature deconvolution
5. Time-variant scaling (unity)
6. Apply datum statics
7. Velocity estimation
8. Normal moveout correction
9. Automatic Residual Statics application
10. First Break Suppression
    100 ms at 55 ft
    380 ms at 2970 ft
    700 ms at 5225 ft
11. Common depth point stack
12. Time Variant filtering
    16-50 Hz at 700 ms
    14-45 Hz at 1400 ms
    12-40 Hz at 2000 ms
    8-40 Hz at 400 ms
13. Time variant scaling

The surveyor and observer logs are downloaded and displayed using the commands:

scons surveylog.view 
scons observerlog.view

This can be done using the data on the tar file by typing:

./surveylog.job
./observerlog.job

I read the surveyor's log and typed the elevations into the spnElev.txt file. The spnElev.txt file contains two columns. The first is the shotpoint number and the second is the elevation. I read the observer's log and typed the relationship between the field record numbers the shotpoint numbers into the recnoSpn.txt file. The file recnoSpn.txt contains two columns. The first column is the field record number and the second column is the shotpoint number. I used a shotpoint number -999999 to reject bad field records. These files are used in the next section to load the trace headers.

Open Data/Open Source: Seismic Unix scripts to process a 2D land line