Monte Carlo simulation of seismogram envelopes in scattering media
Monte Carlo simulation of seismogram envelopes in scattering media
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DOI：
10.1029/1999jb900437
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发表时间：
2000-03
影响因子：
--
通讯作者：
K. Yoshimoto
中科院分区：
文献类型：
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作者：
K. Yoshimoto
分析地方和区域地震的尾波包络是研究以地震波散射和衰减为特征的岩石圈非均匀结构的最有效方法之一。为了合成尾波包络，我们引入了一种称为直接模拟蒙特卡罗方法的数值方案，该方法已被用于气体动力学理论领域。由于算法的简单性，该方法在数值计算的灵活性方面比以前的方法具有几个优点，以将构建现实的地震图包络所需的各种因素结合起来。尾波包络模拟的基础上，包括多次散射，我们表明，地震速度随深度的增加严重影响尾波包络的形状。在浅源地震的合成包络中，可以清楚地看到由于莫霍面速度增加和自由面反射引起的射线弯曲效应。我们的模拟表明，由于正的速度梯度与深度的地震能量在浅深度的停滞放大的包络的振幅。由于这种效应，对于均匀速度模型的先验假设，通过常规方法测量散射系数可能被高估。
The analysis of the seismogram coda envelopes of local and regional earthquakes is one of the most effective strategies for investigating the heterogeneous lithospheric structure characterized by the seismic scattering and attenuation. In order to synthesize the coda envelope we introduce a numerical scheme called the direct simulation Monte Carlo method, which has been used in the field of the kinetic theory of gases. Because of the simplicity of the algorithm the method has several advantages over previous methods in terms of the flexibility of the numerical calculation to incorporate various factors required to construct realistic seismogram envelopes. On the basis of coda envelope simulations, including multiple scattering, we show that an increase of seismic velocity with depth severely affects the shape of the coda envelope. The effects of ray bending due to the velocity increase at the Moho and the reflection at the free surface are clearly found in the synthesized envelope for a shallow earthquake. Our simulation demonstrates that the amplitude of the envelope is magnified by stagnation of seismic energy at shallow depths due to the positive velocity gradient with depth. Because of this effect, for an a priori assumption of a homogeneous velocity model the measurement of the scattering coefficient by conventional methods may be overestimated.