Decadal scale variations in the seismicity rate in the Ridgecrest‐Coso region, part of the Eastern California Shear Zone, included seismic quiescence from the 1930s to the early 1980s, followed by increased seismicity until the 2019 Mw 6.4 and 7.1 Ridgecrest sequence. This sequence exhibited complex rupture on almost orthogonal faults and triggered aftershocks over an area of ∼90 km long by ∼5–10 km wide, which is a fraction of the area of the previously seismically active Indian Wells Valley and Coso range region. During the last 40 yr, the seismicity has been predominantly the result of strike‐slip motion, extending north from the Garlock fault, along the Little Lake and Airport Lake fault zones, and approaching the southernmost Owens Valley fault to the north. The Coso range forms an extensional stepover between these two strike‐slip fault systems. This evolution of a plate boundary zone is driven by the northwestward motion of the Sierra Nevada, and crustal extension along the southwestern edge of the Basin and Range Province. Stress inversion of focal mechanisms shows that the postseismic stress state consists of almost horizontal σ1 and vertical σ2⁠. The σ1 is spatially rotated across the Coso range stepover with σ1‐trending ∼N17° E to the north, whereas, along the Mw 7.1 mainshock rupture, the trend is ∼N6° E⁠. The friction angles as measured between fault strikes and the σ1 trends correspond to a frictional coefficient of 0.75, suggesting average fault strength. In comparison, the mature Garlock fault has a smaller frictional coefficient of 0.28, similar to weak faults like the San Andreas fault. Thus, it appears that the heterogeneously oriented and spatially distributed but strong Ridgecrest‐Coso faults accommodate seismicity at seemingly random places and times within the region and are in the process of self‐organizing to form a major throughgoing plate‐boundary segment.

中文翻译：

---

1930年代至2019年Ridgecrest-Coso地区的地震活动，应力状态和断层样式：不断演化的板块边界段的地震构造

作为加利福尼亚东部剪切带一部分的里奇克雷斯特-科索地区，地震活动率的年代际尺度变化包括从1930年代到1980年代初的地震静止，随后地震活动增加，直到2019年Mw 6.4和7.1 Ridgecrest序列。该序列在几乎正交的断层上表现出复杂的破裂，并在约90公里长，约5-10公里宽的区域引发余震，这是以前地震活跃的印第安维尔斯谷和科索山脉区域的一小部分。在过去的40年中，地震活动主要是走滑运动的结果，从加洛克断层向北延伸，沿着小湖和机场湖断层带向北延伸，到达最南端的欧文斯谷断层。Coso范围在这两个走滑断层系统之间形成了一个扩展的过渡。板块边界带的这种演化是由内华达山脉的西北运动以及沿盆地和Range Province西南边缘的地壳扩展驱动的。震源机制的应力反演表明，震后应力状态几乎由水平σ1和垂直σ2⁠组成。σ1在Coso范围跨度上在空间上旋转，北移σ1趋势为〜N17°E，而沿着Mw 7.1主震破裂，趋势为〜N6°E。在断层走向和σ1趋势之间测得的摩擦角对应于0.75的摩擦系数，表明平均断层强度。相比之下，成熟的Garlock断层的摩擦系数较小，为0.28，类似于San Andreas断层之类的弱断层。