Abstract The 2012 Mw 8.6 Indian Ocean earthquake, the largest instrumentally recorded strike-slip event, has been described as a westward rupture on orthogonal faults that are part of the original oceanic fabric of the region. Reported estimates of its depth vary from 10 to 45 km, while the maximum depth of its inferred rupture extends to ~50–60 km. The complexity of the earthquake is undeniable both in terms of fault geometry and rupture propagation, with debates on the geometry of the causative faults. Results from recent seismic surveys enable a fresh look at the earthquake fault geometry, nucleation depths, and lithospheric rheology. In the present study, these new findings are incorporated into 22 forward models using a revised velocity structure and N-S geometries that flatten with depth. The rupture initiation is modeled in the uppermost mantle (25–30 km) as well as in the upper mantle at ~45 km, the latter of which is 15–20 km below the commonly accepted values of maximum depth for frictional failure. Our study shows that the westward directionality of wave propagation is achieved for strike-slip failure on a listric-like fault, in contrast to subvertical geometries as previously suggested. This propagation is persistent for a strike-slip failure only for events nucleating at upper mantle depths (~45 km) rather than for those set to originate at depths between 25 and 30 km. However, for a dip-slip failure the westward propagation is found to be consistent at both nucleation depths on a listric-like fault. This study highlights a deep nucleation within the lithospheric mantle for the 2012 Mw 8.6 earthquake that could be due to strain localization induced by fluid-rock interaction and/or mineral transformation/crystallization near the 680 °C isotherm at ~45 km depth (≈1.4 GPa), which correlates with deep serpentinization on faults.

中文翻译：

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2012 年 Mw 8.6 印度洋地震：类李斯特断层上的深成核

摘要 2012 年 Mw 8.6 印度洋地震是仪器记录的最大走滑事件，被描述为正交断层向西破裂，正交断层是该地区原始海洋结构的一部分。其深度的报告估计值从 10 到 45 公里不等，而其推断的破裂的最大深度扩展到约 50 到 60 公里。就断层几何形状和破裂传播而言，地震的复杂性是不可否认的，关于成因断层的几何形状的争论。最近的地震勘测结果使我们能够重新审视地震断层的几何形状、成核深度和岩石圈流变学。在本研究中，这些新发现被纳入 22 个使用修正的速度结构和随着深度变平的 NS 几何形状的正向模型中。破裂起始在最上地幔（25-30 公里）和上地幔中模拟，约 45 公里，后者比普遍接受的摩擦破坏最大深度值低 15-20 公里。我们的研究表明，与先前建议的亚垂直几何形状相比，在类似李斯特的断层上的走滑破坏实现了波传播的向西方向性。这种传播仅对于在上地幔深度（~45 公里）处成核的事件，而不是那些起源于 25 至 30 公里深度的事件，对于走滑失败是持续的。然而，对于倾滑破坏，发现向西传播在链状断层上的两个成核深度是一致的。这项研究强调了 2012 Mw 8 岩石圈地幔内的深层成核。