10.0 Seismic data

Any 2D Seismic SEGY data can be loaded into GMG models, however, to be useful, it is highly recommended these data are pre-processed in the depth domain.

As an example, we will download the freely available Society of exploration geophysicists (SEG) Advanced Modeling Program (SEAM) Phase 1 data. This is a synthetic 35 x 40 x 15 km 3D cube that simulates a realistic salt canopy.

These data can be accessed by following this link:

https://seg.org/News-Resources/Research-Data/Open-Data

And then by clicking the link:

Interpretation Challenge I - Depth

This will direct you to a google drive folder containing the data.

Once you have downloaded the directory SEAM_Interpretation_Challenge_1_Depth/ move this to “YOUR_GMG_PATH”/gmg/docs/tutorial/SEISMIC_DATA e.g.:

mv SEAM_Interpretation_Challenge_1_Depth/ "YOUR_GMG_PATH"/gmg/docs/tutorial/SEISMIC_DATA

Now, to plot a profile with GMG lets extract a 2D profile from the 3D volume using an ObsPy routine.

A script is provided with this tutorial to preform the extraction of a profile at Y-location 24 km. This profile passes through a borehole location that can also be loaded into GMG for aiding interpretation.

To run the profile extraction follow these commands:

cd "YOUR_GMG_PATH"/gmg/docs/tutorial/SEISMIC_DATA
mv ../cut_2d_profile.py .
python cut_2d_profile.py SEAM_Interpretation_Challenge_1_Depth.sgy

Note

The next step is not required, but if you have Seismic Un*x installed on your computer, or are willing to install it (see https://github.com/JohnWStockwellJr/SeisUnix), then the following is recommended.

Now, lets use the open source seismic processing package SeismicUnix to apply an automatic gain control (AGC) to our SEGY profile in order to balance the amplitudes before we load the profile into GMG for viewing/interpretation:

segyread tape=2d_profile_24000N.segy verbose=1 endian=0 | segyclean > 2d_profile_24000N.su

sugain agc=1 < 2d_profile_24000N.su > 2d_profile_24000N_agc.su

segyhdrs < 2d_profile_24000N_agc.su hfile=hheader bfile=bheader

segywrite < 2d_profile_24000N_agc.su verbose=1 buff=1 tape=2d_profile_24000N_agc.segy bfile=bheader hfile=hheader

We now have a SEGY file ready for importing to GMG.

Open a new GMG window and create a new model (as outlined in Section 1) with dimensions 35 x 15 km. Now, navigate to the SEGY Data menu in the menubar and select Load SEGY….

You will be prompted by a window in which to enter the dimensions of the SEGY file and name of the segy file. Input the dimensions x = 0 35 and y = 0 15 and give the file a name, e.g. profile_24N. Now select Set Coordinates.

A file explorer will now load. Navigate to the SEGY file (i.e. either 2d_profile_24000N_agc.segy or 2d_profile_24000N.segy) you want to load and select Open.

You should now see the seismic profile in your GMG modelling frame!

Try Changing the color palette from grey scale to Red-white-Blue by using:

Seismic Data -> Color palette -> Seismic

Now try adjusting the display Gain using:

Seismic Data -> Gain -> Increase...

or the left and right arrow keyboard shortcuts.