GEPH316 Seismic Data Processing

Field Data Workshop 2000


Practical outline

The afternoon of 03/03/2000 was spent in the field acquiring a CDP line of seismic reflection data at the Lancaster University Hazelrigg Field Station using a 12 channel digital seismograph, recording the data onto PC disks. The data has been transferred to the University Unix system for display and preliminary processing during this practical session.

Seismic line data file

The data file is available as a binary file line00.seg for off-campus users. This file is about 1.1 Mbyte and should be renamed to line for use with the following Web pages. The reflections are not of very good quality but the line is sufficient to demonstrate some aspects of the Seismic Unix package. The Seismic Unix package may be obtained from the CWP/SU: Seismic Un*x Home Page at the Colorado School of Mines.

Data processing steps

Work through the practical in the following stages. Keep a record of the main features of the various processing steps and the quality of the results, for inclusion in your report.

When starting again part way through the processing sequence, it is possible to restore quickly a past condition using the final Summary worksheet page, which contains just the main processing steps.

Processing stage Action Details
1. Equipment set up: Getting a Unix account; X terminals; Connecting to Unix; Starting Netscape; Dual X windows operation; X windows cut and paste.
2. Environment set up: Setting the Unix environment; Using the scratch file area; Copying the raw seismic data file; Summary - setting everything up.
3. CWP/SU package: CWP/SU Seismic Unix philosophy; Piping files through SU commands; SU on-line help.
Raw Data
Input raw data 4. Survey description: Survey data format; Survey data description; Building the data file.
First examination of data 5. Viewing seismic data: Viewing all the line; Viewing part of a window; Printing all the line; Extracting one shot; Viewing one shot; Inspecting the shots; Removing unwanted graphics windows.
Reduce data 6. Reducing data quantity: Resampling the traces.
Define geometry 7. Trace headers: Viewing a trace header; Changing trace headers; Viewing trace header words; Labelling the whole section.
Pre-processed Data
Kill noisy traces 8. Remove noisy traces: Kill noisy traces.
9. Frequency spectra: Frequency spectra for one shot; Examining the frequency spectra; Resampling the traces; Frequency spectra of different waves; Better frequency spectra by tapering.
10. Frequency filter design: Frequency filter design; Spike series; Normal filter; Butterworth filter.
Frequency filtering 11. Frequency filtering data: Frequency filtering; Low-pass filtering; High-pass filtering; Filtering the complete line.
Statics corrections 12. Statics: Preliminary statics; Datum statics; Inspecting the data; Correlating the data; Shifting the shots; Building the static corrected line.
Mute coherent noise
13. F-K Spectra: Spatial spectra; F-K Fourier spectra; F-K Fourier spectrum for one shot; Apparent velocity; Reflection events
14. F-K filtering: Velocity selection; Dip/slope filtering; Removing low velocity surface waves; Wavenumber aliasing problems; Bias to avoid wavenumber aliasing; Removing the direct waves; F-K filtering the whole line
S/N Enhanced Data
CMP sort 15. Gathers: Types of gather; Common-shotpoint gather; Common-receiver gather; Sorting traces; Common-offset gather; Common-midpoint gather
Velocity analysis 16. Velocity analysis: Fold of gathers; Velocity spectra; Editing the velocity file
NMO correction 17. Normal Moveout Correction: NMO correction of one gather; NMO correction of the whole line
Residual statics 18. Residual statics: Residual statics
Stacking 19. Stacking: Stacking NMO corrected gathers; Stacking the line
Stacked Data
AGC 20. AGC Correction: AGC correction of final section.
Check reflections Attenuate coherent noise
Final seismic section
21. Summary: Complete processing sequence; Setting the environment; Viewing the data; CDP header labels; Frequency filtering; F-K filtering; Common-offset gather; Common-midpoint gather; Velocity analysis; NMO correction; Stacking the line

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Copyright © Brian Robinson 2000. All rights reserved.
Last updated on 8/03/2000 by BR.