Recent observations show that certain rupture phase can propagate backward relative to the earlier one during a single earthquake event. Such back-propagating rupture (BPR) was not well considered by the conventional earthquake source studies and remains a mystery to the seismological community. Here we present a comprehensive analysis of BPR, by combining theoretical considerations, numerical simulations, and observational evidences. First, we argue that BPR in terms of back-propagating stress wave is an intrinsic feature during dynamic ruptures; however, its signature can be easily masked by the destructive interference behind the primary rupture front. Then, we propose an idea that perturbation to an otherwise smooth rupture process may make some phases of BPR observable. We test and verify this idea by numerically simulating rupture propagation under a variety of perturbations, including a sudden change of stress, bulk or interfacial property and fault geometry along rupture propagation path. We further cross-validate the numerical results by available observations from laboratory and natural earthquakes, and confirm that rupture “reflection” at free surface, rupture coalescence and breakage of prominent asperity are very efficient for exciting observable BPR. Based on the simulated and observed results, we classify BPR into two general types: interface wave and high-order re-rupture, depending on the stress recovery and drop before and after the arrival of BPR, respectively. Our work clarifies the nature and excitation of BPR, and can help improve the understanding of earthquake physics, the inference of fault property distribution and evolution, and the assessment of earthquake hazard.

中文翻译：

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反向传播的破裂：性质、激发和影响


最近的观测表明，在单次地震事件中，某个破裂阶段可以相对于先前的破裂阶段向后传播。传统的地震源研究并未充分考虑这种反向传播破裂 （BPR），对于地震学界来说仍然是一个谜。在这里，我们通过结合理论考虑、数值模拟和观测证据，对 BPR 进行了全面分析。首先，我们认为 BPR 就反向传播应力波而言是动态破裂期间的内在特征;然而，它的特征很容易被初级破裂前沿后面的相消干涉所掩盖。然后，我们提出了一个想法，即对原本平稳的破裂过程的扰动可能会使 BPR 的某些阶段可观察。我们通过数值模拟各种扰动下的破裂传播来测试和验证这一想法，包括沿破裂传播路径的应力、体或界面性质以及断层几何形状的突然变化。我们通过实验室和自然地震的可用观测进一步交叉验证了数值结果，并证实自由表面的破裂“反射”、破裂合并和突出凹凸的破损对于激发可观测的 BPR 非常有效。根据模拟和观察结果，我们将 BPR 分为两大类：界面波和高阶再破裂，分别取决于 BPR 到达前后的应力恢复和下降。我们的工作阐明了 BPR 的性质和激励，有助于提高对地震物理学的理解、断层特性分布和演变的推断以及地震危险性的评估。