HR: 0800h
AN: NG31A-0863    [Abstracts]
TI: Preparation for Mainshocks: a Closer Look at Correlation Evolution
AU: * Weatherley, D K
EM: dion@quakes.uq.edu.au
AF: Earth Systems Science Computational Centre, University of Queensland, St. Lucia, Qld 4072 Australia
AU: * Weatherley, D K
EM: dion@quakes.uq.edu.au
AF: Australian Computational Earth Systems Simulator, University of Queensland, St. Lucia, Qld 4072 Australia
AU: Mora, P
EM: morap@quakes.uq.edu.au
AF: Earth Systems Science Computational Centre, University of Queensland, St. Lucia, Qld 4072 Australia
AU: Mora, P
EM: morap@quakes.uq.edu.au
AF: Australian Computational Earth Systems Simulator, University of Queensland, St. Lucia, Qld 4072 Australia
AB: The critical point hypothesis of seismicity proposes that the preparation for large earthquakes involves the progressive formation of long-range spatial correlations in the regional stress field. Smaller earthquakes in the surrounding region are responsible for this correlation evolution. The observable signature of correlation evolution is accelerating seismic energy release, a phenomenon that has been observed in a number of tectonic regions. Accelerating energy release has been observed in earthquake simulations with evidence for correlation evolution obtained by examining the evolution of the two point spatial correlation function of the stress field. These previous studies did not closely examine the correlation evolution within the region affected by the mainshock but rather examined the correlation evolution of the entire modelled region. In cases where mainshocks only affect a fraction of the modelled region, it is difficult to detect correlation evolution. In the current investigation, we re-examine correlation evolution within cellular automaton models of earthquake fault systems. We focus upon stress field evolution only within the region containing sites that fail in a subsequent mainshock. In addition, we track the spatial extent of precursors that alter the stress within the mainshock failure region. This provides a measure of the critical region size for accelerating energy release. We compare power-law fits to cumulative energy release within the critical regions with power-law fits to cumulative energy release within the entire modelled region. Preliminary results indicate there is a systematic reduction in short-range correlations as a mainshock approaches, accompanied by formation of long-range correlations for distances approximately twice the effective interaction range of the model.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 8164 Stresses--crust and lithosphere
DE: 7209 Earthquake dynamics and mechanics
SC: Nonlinear Geophysics [NG]
MN: 2004 AGU Fall Meeting