Figure 1 This is a typical record section shot from point A. Note the low background noise, the coherent first arrivals, the higher frequency airwave, the large surface waves (overly magnified on this plot) and the two different slopes clearly present in the first arriving compressional waves. There are also several regions of spacially coherent waveforms indicative of secondary phases. These are particularly clear on record 18e. All traces are stacked 30 times.
representative records from other shotpoints:
Figure 2 A complete set of P-wave traveltimes was picked for one time (hour 16.5). Again the two-layer velocity structure of the beach is clear. On a gross scale, the lack of symmetry in traveltimes is due to the slope of the beach.
Figure 3 A suitable velocity structure was forward modeled to match the direct waves and the waves refracted in the second layer. All five sets of traveltimes were used for this procedure. No lateral velocity variation was introduced in either of the two layers and only a slight vertical gradient was used to turn the rays. For all pracitcal purposes it is a two layer profile.
Figure 4 This is an example of how the modeled travel times fit the actual data. Data is in orange, predictions are in black. The vertical axis is time in miliseconds. The horizontal axis is distance in meters.
Figure 5 This seismic discontinuity is substantial. The velocity increases from 300 m/s above the discontinuity to 1600 m/s below. If this is interpreted as the water table it implies a depth of about two meters. This compares favorably, but is not identical, to the well measurements.
