Structural Controls Over the 2019 Ridgecrest Earthquake Sequence Investigated by High‐Fidelity Elastic Models of 3D Velocity Structures
Structural Controls Over the 2019 Ridgecrest Earthquake Sequence Investigated by High‐Fidelity Elastic Models of 3D Velocity Structures
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DOI：
10.1029/2020jb021124
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发表时间：
2021-07
期刊：
影响因子：
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通讯作者：
S. Tung;M. Shirzaei;Chandrakanta Ojha;A. Pepe;Zhen Liu
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作者：
S. Tung;M. Shirzaei;Chandrakanta Ojha;A. Pepe;Zhen Liu
我们建立了考虑2019年山脊地震序列（包含Mw7.1和Mw6.4两个主要事件）震中周围三维弹性结构的同震位移场有限元模型。利用干涉合成孔径雷达记录的地表位移场反演了同震滑动分布。利用一种新颖的非线性交叉线性反演方法，进一步优化了破裂倾角几何形状。研究发现，考虑弹性非均质性和断层沿走向曲线改善了对观测位移场的拟合，并能更准确地估计大地力矩和库仑应力变化。我们观察到余震和高滑块的位置与岩石异常弹性性质之间的空间相关性，表明浅层地壳的弹性结构可能控制了脊峰地震序列。在3.6 km深度，7.4 m的同震滑动发生在S波速度降低和明显的Mw7.1后余震区域之上。这意味着黏性物质或流体的存在可能导致了主震的低破裂速度。此外，西北向断裂带上的高滑带横向被两个余震群所包围，其位置以中等岩石刚度为特征。值得注意的是，一些较小的正交断层始终结束于地下刚体之上。总的来说，这些构造控制的观察提高了我们对早期断层系统内地震发生的理解。
We develop finite element models of the coseismic displacement field accounting for the 3D elastic structures surrounding the epicentral area of the 2019 Ridgecrest earthquake sequence containing two major events of Mw7.1 and Mw6.4. The coseismic slip distribution is inferred from the surface displacement field recorded by interferometric synthetic aperture radar. The rupture dip geometry is further optimized using a novel nonlinear‐crossover‐linear inversion approach. It is found that accounting for elastic heterogeneity and fault along‐strike curvilinearity improves the fit to the observed displacement field and yields a more accurate estimate of geodetic moment and Coulomb stress changes. We observe spatial correlations among the locations of aftershocks and patches of high slip, and rock anomalous elastic properties, suggesting that the shallow crust's elastic structures possibly controlled the Ridgecrest earthquake sequence. Most of the coseismic slip with a peak slip of 7.4 m at 3.6 km depth occurred above a zone of reduced S‐wave velocity and significant post‐Mw7.1 afterslip. This implies that viscous materials or fluid presence might have contributed to the low rupture velocity of the mainshock. Moreover, the zone of high slip on the northwest‐trending fault segment is laterally bounded by two aftershock clusters, whose location is characterized by intermediate rock rigidity. Notably, some minor orthogonal faults consistently end above a subsurface rigid body. Overall, these observations of structural controls improve our understandings of the seismogenesis within incipient fault systems.