HR: 16:30h
AN: S24A-03    [Abstracts]
TI: Evolution of Triggered Aftershock Sequences
AU: * Gerstenberger, M C
EM: mattg@usgs.gov
AF: USGS, 525 S. Wilson Ave., Pasadena, CA 91106 United States
AB: It is generally believed that large earthquakes can and do trigger distant large aftershocks. In some cases multiple events can be triggered that take the form of secondary aftershock sequences that are spatially separated from the triggering mainshock and its primary aftershock sequence. However, it is not generally known if these distant triggered sequences show similar aftershock sequence characteristics as the primary sequence (e.g., a similar aftershock decay rate and frequency magnitude distribution). A related question is whether the secondary aftershock sequence is controlled more by the initial mainshock or by the local/secondary mainshock. From a stress change point of view, at some distance from the mainshock the largest local aftershock should begin to dominate the local stress changes and therefore have a dominant influence on the evolution of the secondary aftershock sequence. I will present results from several large sequences to examine if these relationships can be better understood on a case by case basis. Additionally, I will explore an existing, modified Omori law based aftershock forecasting model for its performance in forecasting distant triggered events. In the model, triggering of distant events is effectively controlled by the smoothing of the Gutenberg-Richter $a$ value with distance from the rupturing fault. I will present several models for smoothing the $a$ value and examine if any model generates significantly better forecasts based on a likelihood test.
DE: 7230 Seismicity and seismotectonics
DE: 7200 SEISMOLOGY
SC: Seismology [S]
MN: 2004 AGU Fall Meeting