HR: 08:15h
AN: S41D-02    [Abstracts]
TI: Seismic Hazard Inferred From Tectonics: California
AU: * Bird, P
EM: pbird@ess.ucla.edu
AF: Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567 United States
AU: Liu, Z
EM: liuz@pangea.stanford.edu
AF: Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567 United States
AB: We propose two related hypotheses concerning long-term-averages of shallow seismicity: (1) The long-term seismic moment rate of any tectonic fault, or any large volume of anelastically deforming lithosphere, is approximately that computed using the coupled seismogenic thickness of the most comparable type of plate boundary. (2) The long-term epicenter production of any tectonic fault, or any large volume of anelastically deforming lithosphere, is approximately that computed from its moment rate using the frequency-magnitude distribution of the most comparable type of plate boundary. Suggested rules for assigning the most comparable plate boundary type are presented in tables, and the seismicity parameters of these plate boundaries have already been estimated [Bird & Kagan, 2004]. Long-term forecasts based on these hypotheses do not use the local seismic history in a direct way, so they can give warning of regions which may have been temporarily below their long-term seismicity. A novel proposal implicit in these hypotheses is that even the largest earthquakes may have epicenters located on short faults, or far from mapped fault traces. As an example, we compute the long-term seismicity of the California region based on a long-term-average velocity and strain rate model computed with kinematic finite-element program NeoKinema. This velocity field is a weighted least-squares solution to constraints from plate tectonics, geologic slip rates, geodesy, and stress directions. In the geographic rectangle 31.5~43N, 113.1~125.4W surrounding California, our forecast of 64 m>5.663 earthquakes per 25.75 years exceeds the Harvard CMT catalog count of 48 for 1977.01~2002.09. In the slightly smaller RELM test area, our forecast of 235 m>4.95 earthquakes per 21 years exceeds the ANSS catalog count of 165 for 1984.01~ 2004.12. In the smaller rectangle 32.5~36N, 115~121W in southern California, our forecast of 315 m>5 events per 72.67 years is more than twice the TriNet catalog count of 147 for 1932.01~2004.08. We suggest that California, and especially southern California, may be temporarily below long-term seismicity because of the recent lack of great earthquakes (such as those of 1700, 1857, 1872, and 1906) to stimulate aftershocks.
UR: http://element.ess.ucla.edu
DE: 0550 Model verification and validation
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005