HR: 0800h
AN: S41A-0949    [Abstracts]
TI: Multi-scale dynamic rupture simulation on fractal patch model
AU: * Ide, S
EM: ide@eps.s.u-tokyo.ac.jp
AF: Department of Earth and Planetary Science, 7-3-1 Hongo, Bunkyo, Tokyo, 113-0033 Japan
AU: Aochi, H
EM: h.aochi@brgm.fr
AF: BRGM/ARN/MAS, 3 avenue Claude Guillemin, BP6009 , Olreans, 45060 France
AB: We carried out multi-scale full-dynamic rupture simulations, using our new calculation scheme (Aochi and Ide, GRL, 2004) and a fractal patch model as an approximation of realistic heterogeneity. A basic assumption of this model is that a local slip weakening distance (or fracture energy) at a point is proportional to the size of the minimum asperity which includes that point. Since typical topography of fault surface obeys self-affine fractal statistics, we assumed that the asperity distribution is also represented by a power law. For simplicity we prepared seven different sizes of circular patches as discretized representation of asperities. When the patch radius increases by two, the number of patches decreases by four, where the fractal dimension is 2. The whole model space is a fault plane of 4096x4096 square grids, on which the circular patches are distributed randomly. This space is represented by four 64x64 subspaces on different scales and each subspace is connected to the subspaces on the larger and/or smaller scales by renormalization. The assumed values of initial, yield, and residual stresses are homogeneous across the fault plane. We begin each dynamic rupture simulation with breaking one of the patches of the minimum level. In most cases, the rupture stops immediately after the initiation. Sometimes, the rupture coalesces with adjacent patches, propagates into a patch of next level. Frequency-size distribution of these events is approximated by a power law, which is explained by the probability of interaction between asperities. The probability of triggering of dense patch distribution is high and resultant slope of the power law is less steep. Whole rupture process is spontaneous based on exact elasto-dynamics and slip-weakening law except for the nucleation in the minimum level. Thus we observed very heterogeneous process during the rupture: Rupture directivity, rupture front shape, slip distribution, and moment release functions. Some moment rate functions increase irregularly, which resemble to so-called initial phases observed in real seismic waves. We cannot distinguish small and large events from the initial rise of moment rate functions.
DE: 7260 Theory and modeling
DE: 7209 Earthquake dynamics and mechanics
SC: Seismology [S]
MN: 2004 AGU Fall Meeting