Source parameters for the January 1975 Brawley — Imperial valley earthquake swarm |
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| Authors: | Stephen H Hartzell James N Brune |
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| Institution: | (1) Scripps Institution of Oceanography, Institute of Geophysics and Planetary Physics, University of California, 92093 San Diego, La Jolla, California, USA |
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| Abstract: | The source parameters, moment, stress drop and source dimension are estimated for 61 events from the January 1975 Brawley earthquake swarm. Earthquakes studied range in local magnitude from 1.0 to 4.7. Stress drops range from 1 to 636 bars and increase with source depth. It is estimated that the sedimentary structure of the Imperial Valley amplifies shear waves by a factor of 2 to 3 in addition to the free surface amplification of 2. Estimates of moment from 10 sec surface waves are 4 to 6 times larger than the moment estimated from the relatively flat part of the local body wave spectrum at 1 sec. This may be due to after-slip on the fault, a long thin fault, or partial stress drop. It is shown that the experimentally determined ratio of stress drop to apparent stress should be approximately 4.0 when spectrum integration is used to obtainS-wave energy and theP-wave energy is 1/3 theS-wave energy. |
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| Keywords: | Source parameters Brawley swarm Imperial Valley |
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