HR: 09:30h
AN: S31A-07    [PDF]
TI: Are foreshocks explained by cascades of triggered seismicity: empirical tests and comparison with the Olami-Feder-Christensen SOC model
AU: * Hergarten, S
EM: hergarten@geo.uni-bonn.de
AF: Department of Geology, Geodynamics Research Group, University of Bonn,, Nussallee 8, Bonn, 53115 Germany
AU: Helmstetter, A
EM: helmstet@moho.ess.ucla.edu
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California Los Angeles, 3845 Slichter Hall, Los Angeles, CA 90095-1567 United States
AU: Sornette, D
EM: sornette@moho.ess.ucla.edu
AF: Department of Earth and Space Sciences and Institute of Geophysics and Planetary Physics, University of California Los Angeles, 3845 Slichter Hall, Los Angeles, CA 90095-1567 United States
AU: Sornette, D
EM: sornette@moho.ess.ucla.edu
AF: Laboratoire de Physique de la Matiere Condensee, Universite de Nice-Sophia Antipolis, Parc Valrose, Nice, 09106 France
AB: The observation of foreshocks preceding large earthquakes and the suggestion that foreshocks have specific properties that may be used to distinguish them from other earthquakes have raised the hope that large earthquakes may be predictable. Among proposed anomalous properties are the larger proportion than normal of large versus small foreshocks, the power law acceleration of seismicity rate as a function of time to the mainshock and the spatial migration of foreshocks toward the mainshock, when averaging over many sequences. Using Southern California seismicity, we show that these properties and others arise naturally from the simple model that any earthquake may trigger other earthquakes, without arbitrary distinction between foreshocks, aftershocks and mainshocks. With the quality of available catalogues, we do not find a convincing dependence of the foreshocks precursory properties on the mainshock size. Taken at face value, this would imply that earthquakes (large or small) are predictable to the same degree as seismicity rate is predictable from past seismicity by taking into account cascades of triggering. We also find that cascades of triggering give rise naturally to long-range and long-time interactions, which can explain the observations of correlations in seismicity over surprisingly large length scales. Most of these properties are found at a qualitative level in synthetic earthquake catalogs generated by the OFC spring-block model. Following S. Hergarten and H.J. Neugebauer, Phys. Rev. Lett. 88.238501, 10.1103, 2002, we apply the same analysis to synthetic catalogues generated by the OFC model. In addition, and in contrast with the ETAS model and with observations, we find in the OFC model a dependence of foreshock rate on the size of the mainshock, which can be explained by the concept of the``critical earthquake. In the OFC model, large events are therefore slighly more predictable than smaller events.
DE: 7209 Earthquake dynamics and mechanics
DE: 7223 Seismic hazard assessment and prediction
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2003 Fall Meeting