Numerical Simulation of Fault Zone Guided Waves: Accuracy and 3-D Effects
Numerical Simulation of Fault Zone Guided Waves: Accuracy and 3-D Effects
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断层带导波的数值模拟：精度和 3-D 效应
DOI：
10.1007/978-3-0348-8203-3_11
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发表时间：
2002
影响因子：
2
通讯作者：
Y. Ben‐Zion
中科院分区：
文献类型：
--
作者：
H. Igel;G. Jahnke;Y. Ben‐Zion
摘要-断裂带被认为是由地震速度降低的区域组成的。当震源位于或靠近这些低速带时，会产生导向地震头和陷波，这可能是断裂带深层结构的指示。以上几个断裂带的观测表明，它们是近断层辐射的共同特征，但它们的解释可能非常模糊。已经发展出分析方法来计算断裂带和物质不连续处震源的合成地震记录。这些解可用于平面-平行层状断裂带结构中波传播的精确模拟。然而，目前尚不清楚这种简化几何形状的适度偏差如何影响捕获波运动的产生效率和观测。由于更复杂的模型无法用解析方法求解，因此必须采用数值方法。本文讨论了中等不规则断裂带结构中波的三维有限差分计算。我们研究了材料界面处源数值解的准确性，并讨论了三维结构的一些主导效应。我们还表明，对线源生成的二维解进行简单的数学运算，可以精确地模拟点源产生的三维波传播。模拟结果表明，断裂带的结构不连续性（如断层偏移）大于断裂带宽度对圈闭效率有显著影响，而垂直梯度、断裂带随深度变窄、小尺度构造和中等几何变化对圈闭效率没有显著影响。结果还表明，在浅层断裂带层外和层下位置合适的震源可以在上覆断裂带层中产生可观的导波能量。
Abstract— Fault zones are thought to consist of regions with reduced seismic velocity. When sources are located in or close to these low-velocity zones, guided seismic head and trapped waves are generated which may be indicative of the structure of fault zones at depth. Observations above several fault zones suggest that they are common features of near fault radiation, yet their interpretation may be highly ambiguous. Analytical methods have been developed to calculate synthetic seismograms for sources in fault zones as well as at the material discontinuities. These solutions can be used for accurate modeling of wave propagation in plane-parallel layered fault zone structures. However, at present it is not clear how modest deviations from such simplified geometries affect the generation efficiency and observations of trapped wave motion. As more complicated models cannot be solved by analytical means, numerical methods must be employed. In this paper we discuss 3-D finite-difference calculations of waves in modestly irregular fault zone structures. We investigate the accuracy of the numerical solutions for sources at material interfaces and discuss some dominant effects of 3-D structures. We also show that simple mathematical operations on 2-D solutions generated with line sources allow accurate modeling of 3-D wave propagation produced by point sources. The discussed simulations indicate that structural discontinuities of the fault zone (e.g., fault offsets) larger than the fault zone width affect significantly the trapping efficiency, while vertical properly gradients, fault zone narrowing with depth, small-scale structures, and moderate geometrical variations do not. The results also show that sources located with appropriate orientations outside and below a shallow fault zone layer can produce considerable guided wave energy in the overlying fault zone layer.