The 2019 Ridgecrest, California, sequence includes an Mw 6.4 earthquake on 4 July and an Mw 7.1 mainshock 34 hr later. We perform absolute location of Mw≥1.0 Ridgecrest events using multiple velocity models, station corrections, and a location algorithm robust to velocity model and arrival‐time error. The obtained seismicity is mainly ∼3–12 km deep, with few shallower events. The Mw 6.4 hypocenter is ∼12 km deep, compatible with hypocentral depths of most Mw≥6 earthquakes in southern California. The Mw 7.1 hypocenter, however, is unusually shallow at ∼4 km⁠. The immediate post‐Mw 6.4 seismicity defines a deep, ∼12 km long, southeast–northwest structure containing the Mw 6.4 hypocenter and a shallower, orthogonal, ∼18 km long northeast–southwest structure. These structures have little or no intersection, making the Mw 6.4 event a double earthquake, rupturing first the deeper and then the shallower structure. The ensuing, pre‐Mw 7.1 seismicity extends the southeast–northwest structure northwestwards to within ∼3 km of the future Mw 7.1 hypocenter and illuminates a new crossing structure, whereas small clusters of events within 2 km of the future Mw 7.1 hypocenter activate 3–4 times in pulses from a few hours after the Mw 6.4 event through Mw 7.1 initiation. This pre‐Mw 7.1 seismicity suggests Mw 7.1 rupture initiation activated as an event in the pulsing clusters, and early Mw 7.1 rupture growth was primed by stress changes from the Mw 6.4 rupture and its aftershocks. Moreover, shallow Mw 7.1 nucleation, for which spontaneous rupture growth into a large earthquake is not expected, may have required this incitation by the Mw 6.4 events, a significant complication for hazard estimation. Otherwise, Mw 7.1‐like rupture might not have occurred until much later, perhaps with nucleation at greater depth. The Ridgecrest seismicity defines additional structures around and crossing the main Mw 6.4 and 7.1 rupture zones, but some of this seismicity likely shows delayed activity on pre‐existing faults due to stress changes from the main events and not rupture complexity during the larger events.

中文翻译：

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2019年Ridgecrest地震的绝对位置显示了7.1兆瓦的震源浅，7.1兆瓦的前移和脉动和6.4兆瓦的破裂

2019年的加利福尼亚里奇克莱斯特序列包括7月4日的6.4兆瓦地震和34小时后的7.1兆瓦主震。我们使用多个速度模型，测站校正以及对速度模型和到达时间误差具有鲁棒性的定位算法，对Mw≥1.0Ridgecrest事件进行绝对定位。所获得的地震活动深度主要约为3–12 km，很少发生浅层地震。Mw 6.4震源深度约为12 km，与南加州大多数Mw≥6地震的震中深度兼容。然而，Mw 7.1震中在约4km⁠处异常浅。Mw 6.4之后的直接地震活动定义了一个长约12 km的东南-西北结构，其中包含Mw 6.4震源，以及一个较浅的正交的约18 km的东北-西南结构。这些结构几乎没有交集，因此6.4级地震是两次地震，首先破裂更深的然后是较浅的结构。随后发生的Mw 7.1地震活动将东南-西北结构向西北扩展到未来Mw 7.1震源的约3 km之内，并阐明了一个新的交叉结构，而未来Mw 7.1震源在2 km内的小事件簇激活了3–从Mw 6.4事件发生到启动Mw 7.1，几个小时后产生4次脉冲。兆瓦7.1地震前的地震表明，脉动星团中兆瓦7.1破裂的启动是一个事件，兆瓦7.1破裂的早期增长是由兆瓦6.4破裂及其余震引起的应力变化引起的。此外，Mw 7.1形核较浅，其预期不会自发破裂发展成大地震，可能是由于Mw 6.4事件引起了这种诱因，这是危害估计的重大复杂因素。否则，直到很久以后才可能发生Mw 7.1样的破裂，可能是在更深的核中。Ridgecrest地震活动性定义了Mw 6.4和7.1主破裂区周围并与之相交的其他结构，但由于主要事件的应力变化，这种地震活动中的某些可能显示出对既有断层的活动被延迟，并且在较大事件中并未引起复杂的破裂。