HR: 11:20h
AN: S22A-05    [Abstracts]
TI: Linking Earthquake Size Distribution to Stress
AU: * Schorlemmer, D
EM: danijel@sed.ethz.ch
AF: Swiss Seismological Service ETH Zurich, ETH Hoenggerberg HPP P5, Zurich, 8093 Switzerland
AU: Wiemer, S
EM: stefan.wiemer@sed.ethz.ch
AF: Swiss Seismological Service ETH Zurich, ETH Hoenggerberg HPP P5, Zurich, 8093 Switzerland
AU: Wyss, M
EM: wapmerr@maxwyss.com
AF: WAPMERR, Route de Malagnou 36A, Geneve, 1208 Switzerland
AB: Stress dependence of the size distribution of acoustic emissions and micro earthquakes has already been established in the laboratory and for mining related events. However, can this dependence be extrapolated to earthquakes in general? This requires that the parameter $b$ in the Gutenberg-Richter relation $\log N = a - bM$ cannot be a constant, even for worldwide samples. We demonstrate that the $b$-value of earthquakes systematically varies for different styles of faulting, classified through their rake angles. Determining $b$-values as function of rake angle, we universally find that normal faulting events have the highest $b$-values ($b \approx 1.1$), thrust events the lowest ($b \approx 0.75$), and strike-slip events show intermediate values ($b \approx 0.95$). These values are the average from the five datasets investigated for our study: Harvard CMT, southern & northern California, NEID Kanto-Tokai, and NEID F-Net, all providing high-quality focal mechanisms. These results require that $b$ depends inversely on differential stress, offering a framework that explains a range of observational data. Furthermore, seismic hazard assessment needs to correctly estimate the critical parameter $b$ to avoid errors.
DE: 7223 Seismic hazard assessment and prediction
DE: 7230 Seismicity and seismotectonics
DE: 7200 SEISMOLOGY
DE: 7215 Earthquake parameters
SC: Seismology [S]
MN: 2004 AGU Fall Meeting