Abstract

Following the 28 June 1992 Landers earthquake, a well-developed linear pattern of primary and triggered aftershocks occurred within the Eastern California Shear Zone from near the eastern end of the big bend in the San Andreas to northern Owens Valley. In this article we investigate primary aftershocks on the Calico-Blackwater and Harper fault zones, and triggered aftershocks in Indian Wells Valley (Little Lake fault zone) and the Coso Volcanic Field. These areas are directly northwest of the Landers rupture terminus and fall within the Southern Owens Valley Seismic Gap described by Hill et al. (1985). Focal mechanisms from selected events show dextral slip on northwest-trending faults similar to those that ruptured in the main Landers event. From the cumulative seismicity, we estimated the triggered seismicity rates from the Landers earthquake on the Little Lake fault zone (230 events in the first 10 days to 2.5 events/day during the following 5 months) and the Coso Volcanic Field (250 events in the first 10 days to 3.6 events/day during the following 5 months). Triggered seismicity in the Coso Volcanic Field may have been caused by advective gas overpressure. The continuity of aftershock data agree with a significant shear zone passing through the northern Mojave desert into the southern Owens Valley by way of the Harper fault, Little Lake fault zone, and Coso Volcanic Field. Geologic data (surface faults) also support structural continuity within the zone, with the exception of the Garlock fault.

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