Abstract

Seismograms of 26 underground explosions and two cavity collapses at the Nevada Test Site (NTS) and 26 well-recorded earthquakes in central California recorded by a vertical instrument at Berkeley have been studied. It is demonstrated that the use of source arrays instead of instrument arrays may provide information of general nature about the crust-upper mantle structure. The method can particularly be useful in regional reconnaissance of seismic areas with as few as a single recording instrument.

Times of four consistent arrivals on the NTS seismograms are analyzed. The first two arrivals with observed apparent velocities of 8.51 ± 0.47 and 6.41 ± 0.23 km/sec are interpreted as Pn and Pg phases, respectively. A later arrival, named PLP, with an observed slope corresponding to a velocity of 9.80 ± 0.86 km/sec is consistent with P-wave reflections from a depth of 227 ± 22 km.

The observed phases on the seismograms of central California earthquakes suggest a single-layer crust with an average thickness of 20.5 km to the south of Berkeley. The crustal longitudinal and shear velocities are 5.87 ± 0.05 and 3.46 ± 0.05 km/sec, respectively. The observed Pn and Sn velocities are 7.91 ± 0.12 and 4.40 ± 0.10 km/sec, respectively.

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