The July 2019 Ridgecrest, California earthquake sequence involved two large events, the M6.4 foreshock and the M7.1 mainshock that ruptured a system of intersecting strike-slip faults. We present analysis of space geodetic observations including Synthetic Aperture Radar (SAR) and Global Navigation Satellite System (GNSS) data, geological field mapping, and seismicity to constrain the sub-surface rupture geometry and slip distribution. The data render a complex pattern of faulting with a number of sub-parallel as well as cross-cutting fault strands that exhibit variations in both strike and dip angles, including a “flower structure” formed by shallow splay faults. Slip inversions are performed using both homogeneous and layered elastic half space models informed by the local seismic tomography data. The inferred slip distribution suggests a moderate amount of the shallow coseismic slip deficit. The peak moment release occurred in the depth interval of 3-4 km, consistent with results from previous studies of major strike-slip earthquakes, and the depth distribution of seismicity in California. We use the derived slip models to investigate stress transfer and possible triggering relationships between the M7.1 mainshock and the M6.4 foreshock, as well as other moderate events that occurred in the vicinity of the M7.1 hypocenter. Triggering is discouraged for the average strike of the M7.1 rupture (320 deg), but encouraged for the initial orientation of the mainshock rupture suggested by the first motion data (340 deg.). This lends support to a scenario according to which the earthquake rupture nucleated on a small fault that was more optimally oriented with respect to the regional stress, and subsequently propagated along the less-favorably oriented pre-existing faults, possibly facilitated by dynamic weakening. The nucleation site of the mainshock experienced positive dynamic Coulomb stress changes that are much larger than the static stress changes, yet the former failed to initiate rupture.

中文翻译：

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受空间大地数据和余震位置约束的2019年Ridgecrest地震序列的有限滑移模型

2019 年 7 月加利福尼亚州里奇克莱斯特地震序列涉及两个大型事件，即 M6.4 前震和 M7.1 主震，它们破坏了交叉走滑断层系统。我们对空间大地测量观测进行了分析，包括合成孔径雷达 (SAR) 和全球导航卫星系统 (GNSS) 数据、地质场测绘和地震活动，以限制地下破裂几何形状和滑动分布。数据呈现出复杂的断层模式，其中包含许多次平行以及横切断层链，这些断层链表现出走向和倾角的变化，包括由浅张断层形成的“花状结构”。滑移反演是使用由局部地震层析成像数据通知的均匀和分层弹性半空间模型来执行的。推断的滑动分布表明存在适度的浅层同震滑动缺陷。峰值矩释放发生在 3-4 公里的深度区间，与之前对大走滑地震的研究结果以及加利福尼亚地震活动的深度分布结果一致。我们使用推导出的滑动模型来研究 M7.1 主震和 M6.4 前震之间的应力传递和可能的触发关系，以及发生在 M7.1 震源附近的其他中等事件。不鼓励触发 M7.1 破裂（320 度）的平均走向，但鼓励第一个运动数据（340 度）建议的主震破裂的初始方向。这为这样一种情景提供了支持，即地震破裂在一个小断层上成核，该断层相对于区域应力的方向更佳，随后沿着方向不太有利的预先存在的断层传播，这可能是由动态减弱促进的。主震成核位置经历了比静态应力变化大得多的正动态库仑应力变化，但前者未能引发破裂。