HR: 15:25h
AN: S32D-08    [PDF]
TI: Plate-Tectonic Analysis of Shallow Seismicity: Apparent Boundary Width, beta-Value, Corner Magnitude, Coupled Lithosphere Thickness, and Coupling in 7 Tectonic Settings
AU: * Bird, P
EM: pbird@ess.ucla.edu
AF: Dept. of Earth & Space Sciences, University of California, Los Angeles, CA 90095-1567 United States
AU: Kagan, Y Y
EM: kagan@cyclop.ess.ucla.edu
AF: Dept. of Earth & Space Sciences, University of California, Los Angeles, CA 90095-1567 United States
AB: A new plate model [{\it Bird,} 2003, G$^{3}$, 10.1029/2001GC000252] is used to analyze the mean seismicities of 7 types of plate boundary (CRB continental rift boundary, CTF continental transform fault, CCB continental convergent boundary, OSR oceanic spreading ridge, OTF oceanic transform fault, OCB oceanic convergent boundary, SUB subduction zone). We compare the plate-like (non-orogen) regions of model PB2002 with the CMT catalog to select apparent boundary half-widths, and then assign 95% of shallow earthquakes to one of these settings. A tapered Gutenberg-Richter model of the frequency/moment relation is fit to the subcatalog for each setting by maximum-likelihood. Best-fitting $\beta$ values range from 0.53 to 0.92, but all 95%-confidence ranges are consistent with a common value of 0.61-0.66. To better determine some corner magnitudes we expand the subcatalogs by: (1) inclusion of orogens; and (2) inclusion of years 1900-1975 from the catalog of {\it Pacheco and Sykes} [1992]. Combining both earthquake statistics and the plate-tectonic constraint on moment rate, corner magnitudes include: CRB 7.64$_{-.26}$$^{+.76}$, CTF 8.01$_{-.21}$$^{+.45}$, CCB 8.46$_{-.39}$$^{+.21}$, OCB 8.04$_{-.22}$$^{+.52}$, and SUB 9.58$_{-.46}$$^{+.48}$. Coupled lithosphere thicknesses are found to be: CRB 3.0$_{-1.4}$$^{+7.0}$ km; CTF 8.6$_{-4.1}$$^{+11}$ km; CCB 18$_{-11}$$^{+?}$ km; OSR 0.13$_{-0.09}$$^{+.13}$ km for normal-faulting and 0.40$_{-.21}$$^{+?}$ km for strike-slip; OTF 12$_{-7.1}$$^{+?}$, 1.6$_{-0.5}$$^{+1.4}$, and 1.5$_{-0.6}$$^{+1.2}$ km at low, medium, and high velocities; OCB 3.8$_{-2.3}$$^{+13.7}$ km, and SUB 18.0$_{-10.8}$$^{+?}$ km. Generally high coupling of subduction and continental plate boundaries suggests that here all seismic gaps are dangerous unless proven to be creeping. Generally low coupling within oceanic lithosphere suggests a different model of isolated seismic asperities surrounded by large seismic gaps which may be permanent.
UR: http://moho.ess.ucla.edu/~kagan/kagan.html
DE: 7209 Earthquake dynamics and mechanics
DE: 7223 Seismic hazard assessment and prediction
DE: 8123 Dynamics, seismotectonics
SC: Seismology [S]
MN: 2003 Fall Meeting