The speed at which an earthquake rupture propagates affects its energy balance and ground shaking impact. Dynamic models of supershear earthquakes, which are faster than the speed of shear waves, often start at subshear speed and later run faster than Eshelby’s speed. Here we present robust evidence of an early and persistent supershear rupture at the sub-Eshelby speed of the 2018 magnitude 7.5 Palu, Indonesia, earthquake. Slowness-enhanced back-projection of teleseismic data provides a sharp image of the rupture process, along a path consistent with the surface rupture trace inferred by subpixel correlation of synthetic-aperture radar and satellite optical images. The rupture propagated at a sustained velocity of 4.1 km s^–1 from its initiation to its end, despite large fault bends. The persistent supershear speed is further validated by seismological evidence of far-field Rayleigh Mach waves. The unusual features of this earthquake probe the connections between the rupture dynamics and fault structure. An early supershear transition could be promoted by fault roughness near the hypocentre. Steady rupture propagation at a speed unexpected in homogeneous media could result from the presence of a low-velocity damaged fault zone.

地震破裂的传播速度会影响其能量平衡和震动的影响。超级剪切地震的动力学模型比剪切波的速度快，通常以次剪切速度开始，后来又比Eshelby的速度快。在这里，我们提供了有力的证据，证明在2018年印度尼西亚印尼帕卢7.5级地震的亚埃舍尔比速度下，早期和持续的超剪切破裂。地震数据的慢度增强的反投影沿与合成孔径雷达和卫星光学图像的亚像素相关性推断出的表面破裂痕迹一致的路径，提供了破裂过程的清晰图像。破裂以4.1 km s ^–1的持续速度传播从开始到结束，尽管有大的断层弯曲。远场瑞利马赫波的地震学证据进一步证实了持续的超剪切速度。这次地震的异常特征探讨了断裂动力学与断层结构之间的联系。震中附近的断层粗糙度可以促进早期的超剪切转变。低速损坏的断层带可能导致在均质介质中以无法预料的速度持续破裂传播。