Estimation of Absolute Stress in the Hypocentral Region of the 2019 Ridgecrest, California, Earthquakes
Estimation of Absolute Stress in the Hypocentral Region of the 2019 Ridgecrest, California, Earthquakes
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DOI：
10.1029/2021jb022000
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发表时间：
2021-07-01
影响因子：
3.9
通讯作者：
Fialko, Y.
中科院分区：
文献类型：
--
作者：
Fialko, Y.
地球岩石圈上部脆性部分的强度控制着构造活动区域的变形样式、地表地形、地震活动以及板块构造的发生，但它仍然是地球物理学中最具争议的量之一。在发震深度起作用的应力的直接测量在很大程度上是缺乏的。地震数据（特别是地震震源机制）已被用于推断主应力轴的方向。我表明，震源机制数据可以与来自精确地震位置的信息相结合，不仅对方向，而且对深部绝对应力的大小施加约束。所提出的方法利用共轭断层的相对姿态来评估发震区偏应力和摩擦强度的幅度以及空间非均质性。利用近似平面的地震活动群及其复合震源机制确定相对断层方向（二面角）和滑动方向。在美国加利福尼亚州里奇克莱斯特地区（该地区最近发生了一系列强烈地震）活动共轭断层之间观测到的二面角分布表明，原地摩擦系数为0.4 - 0.6，深度平均剪应力约为25 - 40兆帕，介于“强”断层理论和“弱”断层理论的预测之间。
Strength of the upper brittle part of the Earth's lithosphere controls deformation styles in tectonically active regions, surface topography, seismicity, and the occurrence of plate tectonics, yet it remains one of the most debated quantities in geophysics. Direct measurements of stresses acting at seismogenic depths are largely lacking. Seismic data (in particular, earthquake focal mechanisms) have been used to infer orientation of the principal stress axes. I show that the focal mechanism data can be combined with information from precise earthquake locations to place constraints not only on the orientation, but also on the magnitude of absolute stress at depth. The proposed method uses relative attitudes of conjugate faults to evaluate the amplitude and spatial heterogeneity of the deviatoric stress and frictional strength in the seismogenic zone. Relative fault orientations (dihedral angles) and sense of slip are determined using quasi-planar clusters of seismicity and their composite focal mechanisms. The observed distribution of dihedral angles between active conjugate faults in the area of Ridgecrest (California, USA) that hosted a recent sequence of strong earthquakes suggests in situ coefficient of friction of 0.4-0.6, and depth-averaged shear stress on the order of 25-40 MPa, intermediate between predictions of the "strong" and "weak" fault theories.