The Physics of the Earthquake Source and Radiated Waves: Frequency Dependence, Spatial Distribution, and Directivity in Elastodynamic Models of Repeated Fault Ruptures

这项建议考察了一类新的弹性动力学模型的扩展，这些模型已经成功地模拟了广泛的地震行为，用于研究地震期间产生的辐射能量。由于辐射能量是最丰富的观测数据来源，它最终将为地震模型提供最重要的约束。以前的工作已经研究了总辐射能量如何对震源物理敏感，显示了在弹性动力学断层模型中滑动减弱和速度减弱摩擦的差异。该项目建议更深入地研究辐射能量场，以寻找源物理的进一步特征。首先，该项目不是只研究总辐射能量，而是研究远场辐射能量的光谱含量，检查它作为力矩的函数，以及一定范围的摩擦。在这里，我们可以看到滑动和速度减弱摩擦力的进一步差异。接下来，这项研究将考察辐射的空间相关性，观察当一个人从远场移动到近场时，辐射能量如何变化。在这里，该项目将检查相对于震源的固定半径和角度的平均光谱能量密度，对类似大小的事件进行平均。预计会出现有趣的距离依赖效应，特别是对于距离地壳深度数量级的距离。最后，研究将寻找断层上运动与辐射能量场方面的相关性。具体地说，这些模型显示了当滑动脉冲通过断层上的应力不均匀时滑动和传播速度的变化；这些变化是如何在方向性效应和频谱含量上表现出来的？

This proposal examines the extension of a new class of elastodynamic models, which have already been successful at simulating a wide range of earthquake behaviors, to the study of the radiated energy produced during earthquakes. Because radiated energy is the richest source of observational data, it will ultimately provide the most significant constraints on earthquake models. Previous work has examined how total radiated energy can be sensitive to the earthquake source physics, showing differences for slip weakening versus velocity weakening friction in elastodynamic fault models. This project proposes to look deeper into the radiated energy field to look for further signatures of the source physics. First, rather than looking only at the total radiated energy, the project will investigate the spectral content of the far field radiated energy, examining this as a function of moment, and for a range of frictions. Here we can expect to see further differences for slip versus velocity weakening friction. Next the research will examine the spatial dependence of the radiation, looking at how the radiated energy changes as one moves from the far field to the near field. Here, the project will examine the average spectral energy density for a fixed radius and angle relative to the event hypocenter, averaging over events of similar size. Interesting distance dependence effects are expected, particularly for distances of order a crustal depth away. Finally, the research will look for correlations in the motions on the fault with aspects of the radiated energy field. Specifically, the models show slip and propagation velocity variations as slip pulses pass through stress heterogeneities on the fault; how are these variations manifested in directivity effects and spectral content?