HR: 0800h
AN: S21B-0279    [Abstracts]
TI: Evaluating Short-Term Probability Forecasts of M4+ Earthquakes in California and Western Nevada Since 2001
AU: * Ebel, J E
EM: ebel@bc.edu
AF: Weston Observatory, Boston College, 381 Concord Rd., Weston, MA 02493 United States
AU: Kafka, A L
EM: kafka@bc.edu
AF: Weston Observatory, Boston College, 381 Concord Rd., Weston, MA 02493 United States
AB: Since 2001 we have made a number of forecasts of 10-day time periods of increased probability of earthquakes of M4 or greater (M4+) in California and Nevada. The forecasts are based on observations of non-Poissonian short-term clustering in the M4+ seismicity from 1968 to 2000 for Northern California/Western Nevada and from 1983 to 2000 for Southern California, and they assume that the M4+ earthquake statistics for these earlier time periods can be applied without change to the current and future seismicity. Since 2001, the observed versus expected outcome of the forecasts: for Northern California/Western Nevada has been: 24 forecasts, 10 forecasts expected correct, and 7 correct forecasts. For Central California/Western Nevada it has been: 33 forecasts, 11 forecasts expected correct, 8 correct forecasts. For Southern California it has been: 19 forecasts, 7 forecasts expected correct, 0 correct forecasts. For Northern and Central California and Western Nevada, the difference between the observed and expected number of correct forecasts is statistically insignificant. However, for Southern California the probability of 0 correct forecasts out of 19 trials is only 0.2%. Since 2001, the M4+ seismicity in Southern California shows a strongly regular component with a period between 25-30 days, suggesting a connection to the monthly earth tidal cycle. Our analysis indicates that the temporal pattern of Southern California M4+ seismicity underwent a major change sometime in 2000-2001, even though the average rate of M4+ earthquakes remained constant.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting