Abstract

A local small deformation network in Mexicali Valley (Baja California, Mexico) recorded fault slip, seismicity, and deformation produced by the 16 October 1999 M 7.1 Hector Mine earthquake 260 km away. The network consists of two crackmeters, two biaxial surface tiltmeters, and one broadband seismograph, all recording continuously; these instruments are complemented by other seismological instruments within the valley. Local microearthquakes with clear P and S phases began 2 hours after arrival of the Hector Mine P wave, and earthquakes with M >2.5 (large enough to be located) started about 33 hours after the earthquake. Local seismicity continued, with decreasing frequency, for about 2 weeks after the Hector Mine earthquake. Vertical and horizontal slip and tilt began on the Imperial fault simultaneously with the Hector Mine earthquake seismic wave arrival, which is clearly recorded by the tiltmeters. Deformation recorded by a tiltmeter on the Cerro Prieto geothermal field began about 30 hours after the main event and ended 13 hours later after the occurrence of the largest local earthquake (M 4.1) in this episode. The temporal pattern of seismicity and deformation suggests that deformation is the main process triggered by the Hector Mine earthquake waves in the study area and the transient local seismicity increase is a response to the triggered deformation.

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