Finite difference simulations of seismic scattering: Implications for the propagation of short‐period seismic waves in the crust and models of crustal heterogeneity
Finite difference simulations of seismic scattering: Implications for the propagation of short‐period seismic waves in the crust and models of crustal heterogeneity
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DOI：
10.1029/jb091ib06p06465
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发表时间：
1986-05
影响因子：
--
通讯作者：
A. Frankel;R. Clayton
中科院分区：
文献类型：
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作者：
A. Frankel;R. Clayton
通过有限差分法生成的合成地震图用于研究弹性波和声波在地震速度随机空间变化的二维介质中的散射。这项研究的结果提供了关于短周期（5）传播的重要见解，自相似介质的特征是散射 Q 值随频率恒定，而理论预测指数介质中的表观 Q 值与频率成正比。因此，这些地壳异质性的替代模型可以通过改进地壳 Q 在大于 1 Hz 的频率下的频率依赖性测量来测试，假设散射是这些频率下的大部分衰减的原因。合成尾波时间衰减的测量清楚地表明，尾波衰减的单散射模型在存在中等量的散射衰减（散射 Q ≤ 200）的情况下是不合适的。在这些情况下，使用单次散射理论从尾波衰减率得出的 Q 值与介质的传输 Q 不对应。观察到沿自由表面的接收器阵列观察到的合成波形的互相关取决于介质的相关距离。这里提出的地壳自相似随机介质会产生高频（15-30 Hz）波形变化，类似于孔径数百米的实际小规模地震阵列所报告的波形变化。
Synthetic seismograms produced by the finite difference method are used to study the scattering of elastic and acoustic waves in two-dimensional media with random spatial variations in seismic velocity. The results of this study provide important insights about the propagation of short-period ( 5), the self-similar medium is characterized by a scattering Q that is constant with frequency, whereas theory predicts that the apparent Q in an exponential medium is proportional to frequency. These alternative models of crustal heterogeneity can thus be tested by improved measurements of the frequency dependence of crustal Q at frequencies greater than about 1 Hz, assuming that scattering is responsible for most of the attenuation at these frequencies. Measurements of the time decay of the synthetic coda waves clearly show that the single scattering model of coda decay is not appropriate in the presence of moderate amounts of scattering attenuation (scattering Q ≤ 200). In these cases, Q values derived from the coda decay rate using the single scattering theory do not correspond to the transmission Q of the medium. The cross correlation of synthetic waveforms observed for an array of receivers along the free surface is observed to be dependent on the correlation distance of the medium. The self-similar random medium proposed here for the crust produces waveform variations at high frequencies (15–30 Hz) similar to those reported for actual small-scale seismic arrays with apertures of hundreds of meters.