Determination of Overburden Velocity

A Octave program, direct.m is included with BSU for this purpose. Having established 30 meters for the cross-over distance, we can run bref using the direct arrival option. We issue the command,

bref 0001 3 0 30 1 0 k004.seg k008.seg k009.seg

which uses 3 shots (the hammer and 2 explosives) to generate the required matrices and vectors. The command restricts offsets to less than 30 meters. The files created are

• G0001 System matrix for direct arrivals
• D0001 Data vector with pick times
• E0001 Elevation and station vector for plotting

We start a Octave session, then execute the following command from within the Octave text window,

direct

The program prompts for the above 3 files, and then prompts for the number of shots (3 in this example). The program solves for the overburden velocity and generates a plot. Figure 31 shows the result. The title includes the simultaneous solution for the direct wave velocity.

Figure 31: Solution for overburden velocity is 923 m/s based on k004.seg, k008.seg, and k009.seg.

In the actual project, additional shots were available to obtain increased confidence in direct and refracted wave solutions. The object here is too keep it simple for the reader to follow.