HR: 11:20h
AN: S12A-04    [Abstracts]
TI: Spontaneous rupture dynamics of a planar fault with arbitrary dipping orientation embedded in 3-D elastic half-space
AU: * Chen, X
EM: xfchen@pku.edu.cn
AF: School of Earth and Space Sciences, Peking University, Beijing, 100871 China
AU: Zhang, H
EM: zhanghm@pku.edu.cn
AF: School of Earth and Space Sciences, Peking University, Beijing, 100871 China
AB: In this study, we proposed the boundary integral equation method (BIEM) with exact Green­_s function for half-space to model the dynamic rupture propagation on a planar fault embedded in a half-space. Although the conventional BIEM is flexible and efficient in modeling dynamic rupture on complicated fault systems (Aochi et al., 2000, 2002), it has been restricted to extremely simple medium model, i.e., infinite medium. The reason is that the formulation of the BIEM relies heavily on the existence of suitable Green­_s functions, and only the Green­_s function for an infinite medium has a simple and closed form. Unfortunately, when the simplest Green­_s function is used, the influence of free surface cannot be included without taking the free surface into account. However, for many large earthquakes, especially those in which rupture propagated up to the surface (e.g., the 1999, ChiChi earthquake), the effect of free surface may play an important role in the rupture pattern. For the first time, we introduced the exact Green­_s function for a half-space, which can be expressed as a wave-number integral in frequency domain, into the BIEM, therefore the effect of the free surface is automatically included. The model we considered is an inclined planar fault (the dip angle can vary from 0 to 90 degree) embedded in a half-space, the rupture started from a small patch, and propagated spontaneously. First, we derived the Green­_s functions and their derivatives with respect to spatial coordinates for a half-space based on bases expand. Starting from the representation theorem in general form, we derived the boundary integral equations (i.e., the stress-slip relations on the fault), and removed the hypersingularities in the BIEs following Fukuyama and Madariaga (1995, 1998). Then a simple discretization scheme (Fukuyama and Madariaga, 1998; Aochi et al., 2000) was applied to the BIEs. Since the Green­_s function for a half-space doesn­_t have a simple form, the discretized BIEs involved double integrals. Special attention was paid to decrease the double integrals to single ones, and we finally obtained a series of simplified discrete BIEs. Combined with the slip weakening law, the rupture process can be obtained numerically. We compared the rupture patterns between the two models: a fault embedded in a half-space and that in an infinite space, and found that significant difference when the depth of the fault is small, especially the case in which the fault extends to the free surface. The proposed method can be easily extended into a more complicated model in principal: a fault system embedded in a multilayered half-space, which need further study in the future. However, since more complicated Green­_s function is adopted, the computation is much more expensive than the case of simple Green­_s function.
DE: 7260 Theory and modeling
DE: 7209 Earthquake dynamics and mechanics
DE: 3210 Modeling
SC: Seismology [S]
MN: 2004 AGU Fall Meeting