Back-propagating supershear rupture in the 2016Mw7.1 Romanche transform fault earthquake
Back-propagating supershear rupture in the 2016Mw7.1 Romanche transform fault earthquake
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DOI：
10.1038/s41561-020-0619-9
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发表时间：
2020-08-10
影响因子：
18.3
通讯作者：
Sudhaus, Henriette
中科院分区：
文献类型：
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作者：
Hicks, Stephen P.;Okuwaki, Ryo;Sudhaus, Henriette
地震破裂的传播方式强烈影响潜在破坏性的地面震动。复杂的破裂通常涉及沿多个断层的滑动，这掩盖了断层带摩擦行为的信息。几何上光滑的海洋变换断层板边界为研究断层动力学提供了有利的环境，因为应变沿着单个宽断层带调节，抵消了均质地质。在这里，我们利用附近海底地震仪和全球地震网络的数据，对 2016 年赤道大西洋罗曼什断裂带发生的 7.1 级地震进行了分析。我们表明，这种破裂有两个阶段：（1）向上和向东传播到转换断层与洋中脊相交的较弱区域，然后（2）以超剪切速度向西向断层中心进行不寻常的反向传播。我们认为，弱断层段的深层破裂促进了浅层锁定区域更大的地震滑移。这凸显出即使沿着单个不同断层带的地震也可能是高度动态的。对反向传播破裂的观察很少，并且在破裂模拟中很大程度上不存在反向传播的可能性，并且在危险评估中也没有考虑到这一点。根据对附近海底和全球地震仪记录的数据的分析，在一次地震中，海洋转换断层沿一个方向破裂，然后以超过剪切波传播的速度向后传播。
How an earthquake rupture propagates strongly influences the potentially destructive ground shaking. Complex ruptures often involve slip along multiple faults, which masks information on the frictional behaviour of fault zones. Geometrically smooth ocean transform fault plate boundaries offer a favourable environment to study fault dynamics, because strain is accommodated along a single, wide fault zone that offsets the homogeneous geology. Here we present an analysis of the 2016M(w) 7.1 earthquake on the Romanche fracture zone in the equatorial Atlantic, using data from both nearby seafloor seismometers and global seismic networks. We show that this rupture had two phases: (1) upward and eastward propagation towards a weaker region where the transform fault intersects the mid-ocean ridge, and then (2) an unusual back-propagation westwards at a supershear speed towards the centre of the fault. We suggest that deep rupture into weak fault segments facilitated greater seismic slip on shallow locked zones. This highlights that even earthquakes along a single distinct fault zone can be highly dynamic. Observations of back-propagating ruptures are sparse, and the possibility of reverse propagation is largely absent in rupture simulations and unaccounted for in hazard assessments.In one earthquake, an oceanic transform fault ruptured in one direction and then backwards at a speed exceeding that of shear-wave propagation, according to an analysis of data recorded by nearby seafloor and global seismometers.