HR: 1340h
AN: S53A-1081    [Abstracts]
TI: Nucleation and Propagation of Dynamic Earthquake Rupture Under Constrained Stochastic Shear Stress
AU: * Ripperger, J
EM: ripperger@sed.ethz.ch
AF: Institute of Geophysics, ETH Zuerich, Schafmattstr. 30, Zurich, 8093 Switzerland
AU: Mai, P M
EM: mai@sed.ethz.ch
AF: Institute of Geophysics, ETH Zuerich, Schafmattstr. 30, Zurich, 8093 Switzerland
AU: Ampuero, J
EM: ampuero@erdw.ethz.ch
AF: Institute of Geophysics, ETH Zuerich, Schafmattstr. 30, Zurich, 8093 Switzerland
AB: Nucleation, propagation and arrest of dynamic rupture are strongly influenced by the distribution of shear stress on the fault plane. Whether or not a seismic instability grows into a moderate to large earthquake, but also the temporal properties (propagation velocity, slip velocity) of sustained rupture depend on the statistical properties of the initial stress fields. Though the incipient stresses are not known for future earthquakes, their physically consistent stochastic characterization will help to include effects of rupture dynamics into earthquake scenario calculations for improved near-source seismic hazard assessment. We therefore study the characterization of heterogeneous stress distributions to explore and quantify their effects on nucleation and propagation of dynamic rupture. Our numerical model consists of a planar fault plane in an elastic medium. Friction on the fault follows a linear slip-weakening law, while the frictional coefficients, the critical slip-weakening distance and normal stress are constant across the fault plane. Shear stress is generated using a spatial random field model, constrained to a fractal wave-number spectrum with a flat part below a given corner wavenumber k_c. Tectonic loading is assumed to occur by homogeneously increasing the initial stress. The critical stress state, at which instability occurs, is found approximately by a trial and error procedure. We find that the resulting nucleation zone in general has a complex shape, but whose dimensions can be related to nucleation lengths that have been analytically derived for simple cases. The critical stress load that has to be added to reach the critical state depends on the ratio A(k_{nuc)/A_0. Here A_0 is the spectral amplitude of the initial shear stress in the flat part below k_c and A(k_nuc) is the amplitude at wave number k_nuc associated with the nucleation length. The average stress level at the critical state of nucleation, which controls the temporal evolution of dynamic rupture, also depends on this spectral amplitude ratio. To relate our dynamic modeling to directly observable quantities, we also analyze the macroscopic rupture parameters (seismic moment, moment rate and seismic energy).
DE: 7209 Earthquake dynamics (1242)
DE: 7290 Computational seismology
SC: Seismology [S]
MN: Fall Meeting 2005