Abstract

A sequence of several earthquakes in April 1892 produced significant damage in the towns of Winters, Dixon, Allendale, and Vacaville along the boundary between the southwestern Sacramento Valley and northern Coast Ranges of California. The largest event occurred on 19 April 1892 with a maximum Modified Mercalli intensity of IX and was assigned a moment magnitude (M) of 6.5 based on felt area. These earthquakes occurred within a zone of active crustal shortening accommodated by postulated blind thrust faults. Seismotectonic and structural analyses are used to evaluate the depth, geometry, and segmentation of thrust faults that were the probable sources of the 1892 earthquake sequence. Synthetic ground-motion modeling demonstrates that rupture of a 17-km-long segment of the thrust fault system can produce the magnitude and distribution of intensities documented from anecdotal accounts of the 19 April 1892 earthquake, including probable directivity effects east of the range front. Integrated structural and seismotectonic analyses also are used to interpret the role of inferred geometric segment boundaries in arresting the 19 April 1892 earthquake rupture, and the subsequent occurrence of the 21 April 1892 aftershock.

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