Finite Slip Models of the 2019 Ridgecrest Earthquake Sequence Constrained by Space Geodetic Data and Aftershock Locations
Finite Slip Models of the 2019 Ridgecrest Earthquake Sequence Constrained by Space Geodetic Data and Aftershock Locations
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DOI：
10.1785/0120200060
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发表时间：
2020-08-01
影响因子：
3
通讯作者：
Fialko, Yuri
中科院分区：
文献类型：
--
作者：
Jin, Zeyu;Fialko, Yuri
2019年7月加利福尼亚州里奇克雷斯特的地震序列涉及两个大事件-6.4级前震和7.1级主震，这两次主震打破了相交的走滑断层系统。我们对空间大地测量数据进行了分析，包括合成孔径雷达和全球导航卫星系统数据、地质野外填图和地震活动，以约束地下破裂几何形状和滑动分布。这些数据呈现了一种复杂的断层模式，具有许多近平行和横切的断层链，它们在走向和倾角上都表现出不同，包括由浅层张开断层形成的“花状结构”。滑移反演采用均匀和分层弹性半空间模型，由当地的地震层析成像数据提供信息。推断的滑移分布表明，浅层同震滑移量适中。峰值时刻释放发生在3-4公里的深度区间，与以前对主要走滑地震的研究结果和加州地震活动的深度分布一致。利用推导出的滑动模型研究了7.1级主震和6.4级前震之间的应力传递和可能的触发关系，以及7.1级震中附近发生的其他中等地震。对于7.1级地震破裂的平均走向(320度)，不鼓励触发，但对于初动数据所显示的主震破裂的初始方位(340度)，则鼓励触发。这支持了这样一种情景，即地震破裂在一个相对于区域应力更有利的小断层上成核，随后沿着定向较差的先前存在的断层传播，可能是由于动力减弱。主震成核处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。
The July 2019 Ridgecrest, California, earthquake sequence involved two large events-the M 6.4 foreshock and the M 7.1 mainshock that ruptured a system of intersecting strike-slip faults. We present analysis of space geodetic observations including Synthetic Aperture Radar and Global Navigation Satellite System data, geological field mapping, and seismicity to constrain the subsurface rupture geometry and slip distribution. The data render a complex pattern of faulting with a number of subparallel 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 M 7.1 mainshock and the M 6.4 foreshock, as well as other moderate events that occurred in the vicinity of the M 7.1 hypocenter. Triggering is discouraged for the average strike of the M 7.1 rupture (320 degrees) but encouraged for the initial orientation of the mainshock rupture suggested by the first-motion data (340 degrees). 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.