| Abstract: | Changes in the ratio of compressional to shear seismic wave velocities prior to an earthquake occurrence. Two models have been suggested to explain the mechanism by which the compressional wave velocity is allowed to vary relative to dilatancy; one model requires the influx of water and the other does not. Dry and saturated rock specimens were fractured or allowed to experience stick-slip in an effort to determine the affect of pore water on the compressional velocity. It was found that water had no effect on the arrival time of compressional waves in dilatant rock. Moreover, the value of Vₚ falls off consistently just before the throughgoing fracture (indicated by stress drop) which indicates a severe weakening of the rock, possibly some cataclasis or grain boundary slip occurring prior to the throughgoing fracture. |
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