HR: 1340h
AN: S23A-0287    [Abstracts]
TI: Comparison of Short-term and Long-term Earthquake Forecast Models for Southern California
AU: * Helmstetter, a
EM: agnes@ldeo.columbia.edu
AF: Lamont Doherty Earth Observatory, 61 Route 9W, Palisades, NY 10964 United States
AU: Kagan, Y Y
EM: ykagan@ucla.edu
AF: Earth and Space Sciences, UCLA, 595 Charles Young Drive East, Los Angeles, CA 90095-1567 United States
AU: Jackson, D D
EM: djackson@ucla.edu
AF: Earth and Space Sciences, UCLA, 595 Charles Young Drive East, Los Angeles, CA 90095-1567 United States
AB: Many earthquakes are triggered in part by preceding events. Aftershocks are the most obvious examples, but many large earthquakes are preceded by smaller ones. The large fluctuations of seismicity rate due to earthquake interactions thus provide a way to improve earthquake forecasting significantly. We have developed a model to estimate daily earthquake probabilities in Southern California, using the Epidemic Type Earthquake Sequence model [Kagan and Knopoff, 1987; Ogata, 1988]. The forecasted seismicity rate is the sum of a constant external loading and of the aftershocks of all past earthquakes. The background rate is estimated by smoothing past seismicity. Each earthquake triggers aftershocks with a rate that increases exponentially with its magnitude and which decreases with time following Omori's law. We use an isotropic kernel to model the spatial distribution of aftershocks for small ($M\leq5.5$) mainshocks, and a smoothing of the location of early aftershocks for larger mainshocks. The model also assumes that all earthquake magnitudes follow the Gutenberg-Richter law with a unifom $b$-value. We use a maximum likelihood method to estimate the model parameters and tests the short-term and long-term forecasts. A retrospective test using a daily update of the forecasts between 1985/1/1 and 2004/3/10 shows that the short-term model decreases the uncertainty of an earthquake occurrence by a factor of about 10.
UR: http://moho.ess.ucla.edu/$\sim$helmstet/forecast.html
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting