远震体波有限破裂过程反演敏感性测试及其在汶川地震上的应用

Sensitivity Tests for Teleseismic Body Wave Finite Fault Inversion and its Application to the Wenchuan Earthquake

本文利用远震P和SH波反演得到2008年5月12日汶川大地震(MW=7.9)的一系列有限破裂模型。使用一种基于小波变换的模拟退火非线性反演方法,我们将主断层划分成若干个子断层,在反演时同时确定每个子断层上的滑移量、滑动角、上升时间(risetime)以及平均破裂速度。我们首先根据一个假定的破裂模型生成理论地震图,将该理论地震数据作为输入进行反演,对该有限破裂反演方法进行了一系列测试,以验证反演对断层倾角、平均破裂速度、最大破裂深度等参数的敏感性。然后我们采用4个不同倾角的断层面来对汶川地震远震体波记录进行反演。结果表明,若对只在一个断层面上模拟该地震,30°倾角是个较为合适的值。反演的结果还表明,此次地震有两个主要的能量释放区域,并且主断层面存在倾角变化的可能性。在将来的研究中,可以结合GPS,InSAR测地学以及强震等数据,来对强震的破裂过程做更细致的研究。

We present a series of rupture models of the Wenchuan MW7.9 earthquake based on inverting P and SH teleseismic body waves.A simulated annealing algorithm is used to determine the finite-fault model that minimizes the objective function described in terms of wavelet coefficients.With this approach,we can simultaneously invert for the slip amplitude,slip direction,rise time and rupture velocity.At the first step,experiments conducted on synthetic data are used to assess the ability to recover rupture slip details and teleseismic body waves.We investigate the resolvability of teleseismic body inversion on dip angle,rupture velocity and maximum rupture depth.Then 4 slip models are obtained for the Wenchuan earthquake by applying this method on 4 single fault planes which are specified by different dip angle.We analysis the resolvability of finite fault analysis by using telesesimic data and how to choose a reasonable dip angle for the Wenchuan earthquake.Two asperities are observed on different solutions,and likelihood of change dip is discussed.Incremental improvements in resolving for source complexity will be possible in the near future with more geodetic data and near field seismic data combined with space-based observations.