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

本提案探讨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大范围的地震行为，以研究地震期间产生的辐射能量。由于辐射能是观测数据最丰富的来源，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，显示了弹性动力学断层模型中滑移减弱与速度减弱摩擦的差异。本项目拟深入研究辐射能量场，寻找源物理的进一步特征。首先，该项目将研究远场辐射能量的光谱含量，而不是只关注总辐射能量，并将其作为力矩和摩擦范围的函数进行检查。在这里，我们可以期望看到滑移与速度减弱摩擦的进一步差异。接下来的研究将检查辐射的空间依赖性，观察当一个人从远场移动到近场时，辐射能量是如何变化的。在这里，该项目将检查相对于事件震源的固定半径和角度的平均频谱能量密度，对类似大小的事件进行平均。有趣的距离依赖效应是预期的，特别是对于一个地壳深度的距离。最后，研究将寻找断层运动与辐射能量场各方面的相关性。具体来说，模型显示了当滑动脉冲穿过断层上的应力非均质性时，滑动和传播速度的变化；这些变化如何表现在指向性效应和光谱含量上？

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?