Ground deformation events preceding the Homestead Valley earthquakes

Abstract Hours prior to the Homestead Valley sequence of earthquakes in the south central Mojave Desert (4.7 ≦ M L ≦ 5.2) on 15 March 1979, evidence of ground displacement was recorded at three widely separated points on the periphery of the Mojave block. The displacements were sensed as anomalous water levels on the two major aqueducts in southern California and as a creep step on a United States Geological Survey creepmeter. As well as being on the periphery of the Mojave block, the water level sensors are immediately adjacent to small Neogene faults, while the creepmeter spans the 1857 break of the San Andreas fault near Palmdale. Recalling the well-established geodetic anomaly on the San Andreas fault near Palmdale in early 1979 and the recently documented enhancement of the strike-slip component of microseismic activity on this section of the fault during the same period, we suggest that these events, the ground deformation events discussed herein and the Homestead Valley earthquakes are all aspects of a blockwide strain episode.

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