HR: 0800h
AN: G11A-0760    [Abstracts]
TI: A Preview of the SHIFT Global Seismicity Forecast
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: zliu@ess.ucla.edu
AF: Department of Earth and Space Sciences, University of California, Los Angeles, CA 90095-1567 United States
AB: Project SHIFT (Seismic Hazard Inferred From Tectonics) will produce global maps of forecast long-term-average (Poissonian) seismicity, at a variety of magnitude thresholds, as well as derived maps of shaking hazard. The basic assumption is that shallow seismicity is proportional to fault slip rates and/or anelastic strain rates in the shallow frictional part of the lithosphere. Historical seismicity is used only to calibrate this relationship. The kinematic surface-velocity model is a composite of (1) global plate model PB2002 of Bird [2003, G$^{3}$] for simple boundaries between the quasi-rigid parts of the 52 plates; (2) local high-resolution models of 13 non-rigid orogens, fit to geologic, geodetic, and stress data using kinematic F-E program NeoKinema; (3) anelastic strain rate estimates in plate interiors, based on a realistic nonlinear rheology and a computed stress field from dynamic F-E program Shells. Tectonic motion is converted to long-term seismicity (earthquakes/m$^{2}$/s above some threshold) based on the calibration study of Bird & Kagan [2004; BSSA], which used 20$^{th}$-century seismicity to determine apparent boundary half-widths, coupled lithosphere thicknesses, beta values, and corner magnitudes for each of 7 plate-tectonic settings. A preview map of the global seismicity forecast above threshold magnitude 5.663 (moment 3.5x10$^{17}$ N m) will be displayed for discussion and comment, although only 2 of 13 orogens (Persia-Tibet-Burma and Gorda-California-Nevada) have been modeled to date. Future plans include (a) replacement of the current "Earth3" Shells model for strain-rates in plate interiors with an "Earth5" model having 4x better resolution and optimized boundary conditions; (b) modeling of the other 11 orogens with NeoKinema; (c) computation of shaking hazard based on seismicity, by traditional methods. It is hoped that the SHIFT long-term seismicity forecasts will provide a firm foundation for more advanced studies of the time-dependence of seismicity, and of the spatial distribution of creeping fault patches.
UR: http://element.ess.ucla.edu
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 1206 Crustal movements--interplate (8155)
DE: 1208 Crustal movements--intraplate (8110)
SC: Geodesy [G]
MN: 2004 AGU Fall Meeting