Following the October 1, 1987 Whittier, California earthquake, portable seismic recording instruments from the refraction group of the USGS at Menlo Park, CA were deployed in the vicinity of the epicenter for a seismic velocity calibration shot. Since the time and place of the shot was known accurately, first arrival times of the seismic energy, Pg, could be measured. With a better understanding of the velocities around the epicenter, the hypocenter for this earthquake and the geological structure in the area could be better constrained.
Notes
no official USGS report number but there is a report
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