Abstract

Although surface ruptures of the principal Landers faults apparently slipped co-seismically, surface slip on the 10-km-long Eureka Peak fault has continued at a decreasing rate during the year following the mainshock. Three creepmeters installed on the fault as early as 4 days after the mainshock have recorded afterslip amplitudes of more than 8 cm on the northern half of the mapped fault. The maximum observed slip 1 yr after the earthquake is 23 ± 2 cm, and an additional 1 to 3 cm of afterslip may occur on the fault in the next decade if the current rate of slip decrease remains steady. Should this occur, it will bring surface slip amplitudes close to the ∼25 cm of slip inferred from geodetic data to have occurred at depth on the northern 4 km of the fault. Creepmeters on the fault record both episodic creep events and slow background slip, but, although changes in creep rate occur, they do not correlate well with seismic moment release in volumes near the fault zone. As is the case with many afterslip processes and other creeping faults in California, the Eureka Peak fault cuts through sediments. It is possible that such sedimentary layers, and corresponding depths to which afterslip is occurring, are relatively shallow or that the fault lacks a well-developed gouge zone near sites where episodic creep is absent.

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