HR: 08:00h
AN: S51F-01 INVITED     [Abstracts]
TI: Rupture propagation and seismic energy radiation along fault surfaces of fractal characteristics
AU: * Ide, S
EM: ide@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Sciences, University of Tokyo, 7-3-1, Hongo, Bunkyo, Tokyo, 1130033 Japan
AU: Aochi, H
EM: H.Aochi@brgm.fr
AF: BRGM, 3 avenue Claude Guillemin, BP6009, ORLEANS, 45060 France
AB: We study rupture propagation in a 2D/3D infinite elastic medium with a slip-weakening friction law and heterogeneous distribution of slip-weakening distance, Dc. Ide and Aochi (2005 JGR) numerically demonstrated statistically self-similar rupture growths in a 3D space using a set of circular patches that obey a power-law size statistics. They showed that the rupture propagation velocity was sub-shear in average, but it could exceed S-wave velocity locally. Moment rate functions of most events had initial phases, but these were useless to predict the final event size. Seismic energy radiation from each model scaled linearly with seismic moment as expected from the self-similarity. We present a simple 2D model of shear crack growth to further investigate the effects of fractal property and Dc scaling. We define the local values of Dc to be proportional to the size of asperities, which is measured on a randomly generated fractal surface in the macroscopic slip direction, and calculate the Dc distribution multiplying a proportionality constant A. The initial, yield, and residual stresses are homogeneous over entire model area except within an initial nucleation area where Dc value is a local minimum. Changing the values of Dc and A, we simulate spontaneous rupture propagation from numerous local minimums. Each rupture is calculated till it stops spontaneously (stopped event) or breaks the entire model space (non-stopping event). We use a boundary integration equation method with a renormalization technique developed by Aochi and Ide (2004). When D = 1, most ruptures naturally stop and the probability of rupture arrest is almost constant at any size. The ratio of non-stopping events increases as A decreases and D increases. At the limit to D = 2, where the topography becomes white noise, it is natural that such high irregularity acts as a spatially uniform Dc and no rupture stops once starts. For these non-stopping events, the final rupture area should be determined by other factor such as stress heterogeneity that is not considered in the present model. For many stopped events, we observe dynamic behavior similar to those visible in our 3D circular patch simulation, such as average sub-shear rupture propagation, local acceleration and deceleration of rupture front, and initial phase in radiated seismograms. The ratio between seismic energy and seismic moment is almost constant for the stopped events except for very small ones.
DE: 4440 Fractals and multifractals
DE: 7209 Earthquake dynamics (1242)
DE: 7223 Earthquake interaction, forecasting, and prediction (1217, 1242)
SC: Seismology [S]
MN: Fall Meeting 2005