Abstract

The 10 April 1947, Manix, California, earthquake (ML = 6.2) is the largest earthquake to have occurred in the Mojave block in historic time. Left-lateral movement was observed along the Manix fault (strike of N70°E) following the earthquake; however, the large aftershocks of the sequence, as located by Richter and Nordquist (1951), align themselves along a trend of N30°W. This led Richter (1958) to conclude that rupture during the main shock was along the trend of the aftershocks and that the surface faulting was a secondary feature. In this study, relocation of the larger aftershocks of the sequence verifies the previously observed trend of N30°W, suggesting the aftershocks occurred along a fault conjugate to the Manix fault. Body waveform modeling of the main shock indicates that it was composed of two subevents. The location of the second subevent with respect to the first subevent suggests unilateral rupture to the southwest along the Manix fault, although the focal mechanisms of both events are consistent with either faulting along the Manix fault or a conjugate fault. Both subevents occurred at relatively shallow depths (5 to 7 km). A study of other recent earthquakes of ML ≧ 3.0 within the Mojave block indicates that the majority of earthquakes in the region occur at shallow depths (<7 km), although the heat flow in the area is 10 to 20 mW/m2 lower than in surrounding regions where deeper seismicity is present.

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