HR: 09:45h
AN: S31D-08    [Abstracts]
TI: Repeating earthquakes may indicate a relation between fault healing and proximity to a mainshock asperity
AU: * Peng, Z
EM: zpeng@ess.ucla.edu
AF: ESS, UCLA, Los Angeles, CA 90095 United States
AU: Vidale, J E
EM: vidale@ucla.edu
AF: ESS, UCLA, Los Angeles, CA 90095 United States
AU: Marone, C J
EM: cjm38@psu.edu
AF: Dept. of Geosciences, Pennsylvania State Univ., University Park, PA 16802 United States
AU: Rubin, A
EM: arubin@princeton.edu
AF: Dept. of Geosciences, Princeton Univ., Princeton, NI 08554 United States
AB: We analyze time-dependent variations in recurrence interval (Tr) and seismic moment (Mo) of 92 repeating earthquake sequences on the Calaveras fault that were aftershocks of the 1984 M6.4 Morgan Hill, California, earthquake. The recurrence interval between successive repeating events is proportional to the time elapsed since the mainshock, and is compatible with the Omori law for aftershock decay. Our results agree with previous inferences that the repeating earthquakes are produced by asperities undergoing stick-slip failure and are reloaded by transient creep after the mainshock. Rates of deep repeating earthquakes diminish faster than those of the shallow events, suggesting a variation in the duration of the postseismic transient within the aftershock zone. We also examine relation between Mo and Tr for these repeating clusters, which we use as a proxy for fault-healing rate. The moment increases 26$\pm$24% per decade change in Tr for clusters located above 5.5 km depth, consistent with our previously published estimates. Most of the clusters that are located below 5.5 km have lower or even negative trends in moments (-3$\pm$11%). The deep repeating events appear to be just above a large asperity that broke during the Morgan Hill mainshock. The asperity is $\sim$10 km deep and has a radius of $\sim$5 km. We consider models in which fault healing is influenced by evolution of fluid pressures in the fault zone, differences in rock type, and the influences of temperature, shear and normal stress on healing, and how these properties may be related to the location of the mainshock asperity.
DE: 8164 Stresses--crust and lithosphere
DE: 7200 SEISMOLOGY
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting