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 2016 M_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.

地震破裂如何传播强烈影响潜在的破坏性地面震动。复杂的破裂通常涉及沿着多个断层的滑动，这掩盖了有关断层带摩擦行为的信息。几何上平滑的海洋变换断层板边界为研究断层动力学提供了一个有利的环境，因为应变是沿着单个宽阔的断层带提供的，这抵消了同质地质。在这里，我们对2016年M _w进行分析 使用来自附近海底地震仪和全球地震网络的数据，在赤道大西洋的罗曼奇断裂带发生7.1级地震。我们表明，这种破裂有两个阶段：（1）向较弱的区域向上和向东传播，在该区域中转换断层与大洋中脊相交，然后（2）以超剪切速度向西异常向后传播，向着中部。错误。我们认为，对弱断层的深层破裂有利于浅层锁定带更大的地震滑动。这突出表明，即使是沿着单个不同断层带的地震也可能是高度动态的。反向传播破裂的观察很少，并且在破裂模拟中基本上没有反向传播的可能性，而在危害评估中却没有考虑。