Data processing

Figure  shows a super-gather, consisting of all the traces in the survey binned as a function of offset. The left panel shows the raw data, and the center panel shows the same data after pre-processing.

 

sgather
Figure 5 Super-gather: entire dataset stacked into offset bins. Left panel shows raw data, center panel show processed data after pre-processing, and right panel shows semblance scan

We processed the data with our in-house software, SEPlib3D, which provides a flexible environment for research in 3-D seismology. The simple processing flow consisted of:

1.

Trace edits

2.

Groundroll removal: A low-cut filter was sufficient to remove the groundroll. See Figure  for its impulse response and spectrum.

3.

Top mute to remove the refracted arrivals.

4.

Time-varying gain correction: tpow=2.

5.

NMO and stack: The right panel of Figure  shows a semblance scan from the super-gather. The velocity information provided by the 3-D dataset was limited by the small maximum offset. However, the small maximum offset also means the dataset is not very sensitive to move-out velocity. In any case, NMO was applied with a constant velocity of 240 m/s, the RMS velocity of the water-table reflector, which had been more accurately estimated from the larger offset 2-D surveys.

 

impulse Figure 6 Impulse response of low-cut filter.