HR: 08:15h
AN: S21C-02    [Abstracts]
TI: Forecasting the evolution of seismicity in southern California: Animations built on earthquake stress transfer
AU: * Stein, R S
EM: rstein@usgs.gov
AF: U.S. Geological Survey, MS 977, Menlo Park, CA 94025 United States
AU: Toda, S
EM: s-toda@aist.go.jp
AF: Active Fault Research Center, Geological Survey of Japan, AIST, Tsukuba, 305-8567 Japan
AU: Richards-Dinger, K
EM: Keith.richards-dinge@navy.mil
AF: Geothermal Program Office, Naval Air Weapons Station, China Lake, CA 93555 United States
AU: Bozkurt, S B
EM: sbozkurt@usgs.gov
AF: U.S. Geological Survey, MS 977, Menlo Park, CA 94025 United States
AB: We develop a forecast model to reproduce the spatial and temporal distribution of M$>$1.4 seismicity for a succession of large earthquakes observed during 1986-2003 in a 300 x 310 km area centered on the M=7.3 Landers earthquake. To parse the catalog into frames with roughly equal numbers of aftershocks, we animate the seismicity in log-time increments that lengthen after each mainshock, revealing aftershock zone migration, expansion and densification. To predict seismicity, we implement a rate/state algorithm that is updated for the stress transferred by each M$>$6 shock, and then evolves. In this model, Coulomb stress changes act to amplify the background seismicity. Small stress changes can produce large seismicity rate changes in areas of high background seismicity. Similarly, seismicity rate declines are evident in the stress shadows only in areas with previously high seismicity rates. Thus a key constituent of the model is the background seismicity rate, which we smooth from 1981-1986 seismicity. The correlation coefficient between observed and predicted shocks is 0.52 for 1986-2003, and 0.63 for 1992-2003; a control standard aftershock decay model yields 0.54 and 0.52 for the same periods. All four M$>$6.0 events that occurred after the test period begin struck in areas of high expected seismicity; three locate at sites where the expected seismicity rate falls above the 92 percentile, and one above the 75 percentile. The model reproduces much, but certainly not all, of the observed spatial and temporal seismicity distribution, from which we infer that the decaying effect of stress transferred by successive mainshocks influences seismicity for decades. Finally, we offer a M$>$5 earthquake forecast for 2005-2015, assigning probabilities to 324 10 x 10-km cells.
UR: http://quake.usgs.gov/$\sim$ross
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7260 Theory and modeling
SC: Seismology [S]
MN: 2004 AGU Fall Meeting