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On January 24, 1980, an earthquake of magnitude 5.9 occurred on the Marsh Creek-Greenville fault system 17 km north of Livermore, California. A single foreshock preceded the earthquake and approximately 600 aftershocks followed during the next 33 days. The largest aftershock, occuring 2Y2.-days later, had a magnitude of 5.3 and located 14 km southeast of the main shock. Fault-plane solutions from P-wave first motions suggest that the focal mechanisms for the main and most aftershocks consist predominantly of dextral strike-slip movement on fault planes striking north to northwest. The distribution of P and T axes are indicative of NE-SW compression of the Livermore Valley. These data are consistent with geologic field mapping showing dextral movement on the Marsh Creek-Greenville fault system. Seismic moments canputed for 24 the main shock and largest aftershock are 6 X 10 and 1.5 X 101 ' 1i/ dyne-cm.
Cockerham et al. (Tue,) studied this question.