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Authors: Sammis, C. G.* 
Rice, J. R.* 
Title: Repeating Earthquakes as Low-Stress-Drop Events at a Border between Locked and Creeping Fault Patches
Journal: Bulletin of the Seismological Society of America 
Series/Report no.: 91/3(2001)
Publisher: Seismological Society of America
Issue Date: Jun-2001
Subject Classification04. Solid Earth::04.06. Seismology::04.06.01. Earthquake faults: properties and evolution 
04. Solid Earth::04.06. Seismology::04.06.03. Earthquake source and dynamics 
Abstract: The source of repeating earthquakes on creeping faults is modeled as a weak asperity at a border between much larger locked and creeping patches on the fault plane. The x^(-1/2) decrease in stress concentration with distance x from the boundaryis shown to lead directly to the observed scaling <T>~<M0>^(1/6) between the average repeat time and average scalar moment for a repeating sequence. The stress drop in such small events at the border depends on the size of the large locked patch. For a circular patch of radius R and representative fault parameters, Dr = 7.6(m/R)3/5 MPa, which yields stress drops between 0.08 and 0.5 MPa (0.8–5 bars) for R between 2 km and 100 m. These low stress drops are consistent with estimates of stress drop for small earthquakes based on their seismic spectra. However, they are orders of magnitude smaller than stress drops calculated under the assumption that repeating sources are isolated stuck asperities on an otherwise creeping fault plane, whose seismic slips keep pace with the surrounding creep rate. Linear streaks of microearthquakes observed on creeping fault planes are trivially explained by the present model as alignments on the boundaries between locked and creeping patches.
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