Earthquakes of strike-slip type in central california: evidence on the question of dilatancy.
The travel times of compressional waves from quarry explosions of well-known origin times, measured at the University of California network of seismographic stations for the period 1961 to the present, have been examined for evidence of premonitory changes prior to earthquakes of moderate magnitudes in the region. Velocities to seven station sites are generally constant to within +/- 1 percent, with occasional deviations of +/- 2 percent. Variations seem to bear no correlation to earthquake occurrence and are probably due to a combination of reading errors and changes in the source location within the quarry.
McEvilly
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Johnson
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