Dynamics and Near‐Field Surface Motions of Transitioned Supershear Laboratory Earthquakes in Thrust Faults
Dynamics and Near‐Field Surface Motions of Transitioned Supershear Laboratory Earthquakes in Thrust Faults
复制标题
DOI：
10.1029/2021jb023733
复制
发表时间：
2022-03
期刊：
影响因子：
--
通讯作者：
Y. Tal;V. Rubino;A. Rosakis;N. Lapusta
中科院分区：
文献类型：
--
作者：
Y. Tal;V. Rubino;A. Rosakis;N. Lapusta
我们研究了逆冲断层的非对称几何形状如何影响超剪切破裂及其相关的尾随瑞利破裂的动力学，因为它们与自由表面相互作用，并调查由此产生的近场地面运动。地震是通过沿沿着摩擦界面传播的实验室破裂来模拟的，摩擦界面倾角为61°。使用一种实验技术，结合高速摄影与数字图像相关，我们产生了粒子位移和速度的全场演变测量序列。我们的全场测量能力使我们能够确认和量化上盘和下盘的实验运动之间的不对称性，在上盘出现更大的速度幅度。有趣的是，由于上盘的运动通常接近垂直，而下盘的运动在倾向方向上比断层倾角浅，因此发现下盘的水平表面速度分量大于上盘。地表速度随距断层道距离的衰减一般在上盘比在下盘大，垂直分量比水平分量更明显。在表面运动的旋转测量实验证实，破裂与自由表面的相互作用可以解释通过扭转机制，导致逆冲地震的自由表面附近的正应力减少。无量纲分析表明，实验测量与大规模数值模拟以及逆冲地震的现场观测一致。
We study how the asymmetric geometry of thrust faults affects the dynamics of supershear ruptures and their associated trailing Rayleigh ruptures as they interact with the free surface, and investigate the resulting near‐field ground motions. Earthquakes are mimicked by propagating laboratory ruptures along a frictional interface with a 61° dip angle. Using an experimental technique that combines ultrahigh‐speed photography with digital image correlation, we produce sequences of full‐field evolving measurements of particle displacements and velocities. Our full‐field measurement capability allows us to confirm and quantify the asymmetry between the experimental motions of the hanging and footwalls, with larger velocity magnitudes occurring at the hanging wall. Interestingly, because the motion of the hanging wall is generally near‐vertical, while that of the footwall is at dip direction shallower than the dip angle of the fault, the horizontal surface velocity components are found to be larger at the footwall than at the hanging wall. The attenuation in surface velocity with distance from the fault trace is generally larger at the hanging wall than at the footwall and it is more pronounced in the vertical component than in the horizontal one. Measurements of the rotations in surface motions confirm experimentally that the interaction of the rupture with the free surface can be interpreted through a torqueing mechanism that leads to reduction in normal stress near the free surface for thrust earthquakes. Nondimensional analysis shows that the experimental measurements are consistent with larger‐scale numerical simulations as well as field observations from thrust earthquakes.