P – SV Statics Computation

Two sets of SEGY files are required, one containing P-P data and the other containing P-SV. The basic steps are as follows:

  1. Create a new Flatirons project using the P-P data and perform delay time analysis as usual, including model generation.
  2. Import the P-SV data into a second Flatirons project and pick first breaks.
  3. Import all of the delay time information from the P-P project into the P-SV project.
  4. Reassign branches in the P-SV project
  5. Use the P wave shot delay times and refractor velocities to compute shear wave receiver delay times.
  6. Compute the shear wave weathering velocity using the physical model imported from the P-P project
  7. Compute shear wave statics

Synthetic data generation

This step is of course optional. Download and install the Flatirons++ (Centos, CPU, GPU) application launcher. Note that no license is required run Flatirons++ or to create synthetics, although separate licenses are required to run Phoenix and PickX.

The refractors are assumed to be perfectly flat, making P-P and P-SV travel times easily computable.

Open the synthetics dialog. Be sure to select the “P-P and P-SV” SEGY output option. Poisson’s ratio is computed at each receiver location and put in the SEGY trace header.

The first break pick times are also stored in the trace headers and may be imported to speed up the following analysis.

Import the P-P data and create a delay time solution

Detailed steps will not be provided here. For the demo synthetic data two refractors are defined in the branch window:

Run the default delay time analysis as usual, then create a model using whatever method you feel is appropriate for your data. For the demo synthetic data the model is created using a weathering velocity of 1000 m/s – this is the weathering velocity used when the synthetics were created. This results in a model almost exactly correct:

Import the P – SV data and pick first breaks

Follow the usual procedures to import the P-SV SEGY files and pick first breaks.

At this point the Flatirons P-SV menu will guide you through the remaining steps.

Import the P-P delay time analysis information

Under the “P-SV” menu select the first item – “Import P-wave delay time data…”. This step imports the shot and receiver P-wave delay times, the refractor velocities, and the refractor elevations:

As a QC it’s a good idea to view the imported data (delay times, velocities, etc) on the basemap.

Branch assignment

It’s critical to make sure the branch assignment is correct for the P-SV picks. Under the “P-SV” menu select the second item, “Check branch assignment…”. Note that the offset ranges for the P-SV data do not match the P-P offset ranges.

Compute the receiver shear wave delay times

Under “P-SV” select the third item, “Compute shear wave receiver delay times”. Shear wave delay times will be interpolated to the shot locations.

View the resulting shear wave delay times on the basemap to make sure they’re valid:

Compute the shear wave velocities

Simply select the fourth menu item. This computation uses the refractor velocities and elevations imported from the P-P project. View the results on the basemap and on the profile display window.

Compute shear wave statics

Select the fifth menu item.