Along-strike variations in the Nankai shallow decollement properties and their implications for tsunami earthquake generation
Along-strike variations in the Nankai shallow decollement properties and their implications for tsunami earthquake generation
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DOI：
10.1002/2014gl061096
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发表时间：
2014-10-28
影响因子：
5.2
通讯作者：
Bangs, Nathan L.
中科院分区：
文献类型：
--
作者：
Park, Jin-Oh;Naruse, Hajime;Bangs, Nathan L.
俯冲带的慢海啸地震破裂沿着一个浅的板块边界断层（即，几乎一直延伸到海沟。地震反射剖面显示，南海俯冲带中的浅层滑脱层具有不同的反射特征，可以将俯冲带分为阻抗减小（推测为富含流体）和阻抗增大（流体贫乏）的滑脱区。由于流体压力升高，具有反极性反射的富含流体的滑脱区域可能起到条件稳定斑块的作用。与此相反，流体贫乏的滑脱区与正常极性的反射可能是不稳定的孕震斑块，没有异常的流体压力。我们认为，当大逆冲断层地震在浅部成核时，小的不稳定的流体贫乏斑块容易滑动。它们也可能加速（速度减弱）邻近的大的、条件稳定的斑块，产生大的浅层滑动和大海啸。因此，断层性质沿走向的差异可能涉及大海啸地震沿着南海浅层巨型逆冲断层。
Rupture of slow tsunami earthquakes at subduction zones propagates along a shallow plate-boundary fault (i.e., decollement) nearly all the way to the trench. Seismic reflection profiles reveal that the shallow decollements have variable reflection characteristics in the Nankai subduction zone, allowing us to divide the subduction zone into impedance-decreasing (inferred to be fluid-rich) and impedance-increasing (fluid-poor) decollement regions. The fluid-rich decollement regions with reverse-polarity reflections may play a role as conditionally stable patches because of elevated fluid pressures. In contrast, the fluid-poor decollement regions with normal-polarity reflections could be unstable seismogenic patches with no unusual fluid pressures. We propose that when megathrust earthquakes nucleate at shallow depth, the small unstable fluid-poor patches are prone to slip. They may also accelerate (velocity-weakening) adjacent large, conditionally stable patches, generating large shallow slip and large tsunamis. As a result, along-strike contrast of fault properties can involve large tsunami earthquakes along the Nankai shallow megathrust fault.