Seismic Swarm S20220715.1: Activity Near Ridgecrest, California

A seismic swarm designated S20220715.1 occurred 14 km northeast of Ridgecrest, California, beginning at 05:09 on 14 July 2022 and concluding at 09:05 on 18 July 2022. Over 99 hours and 56 minutes, the sequence produced 55 earthquakes. Depths ranged primarily between 6 km and 11 km, with the majority clustered around 7–10 km. The largest event reached magnitude 4.5 at 01:19 on 15 July 2022 at a depth of 6 km. Subsequent activity included multiple events between magnitudes 1.0 and 2.3, with the sequence tapering to smaller magnitudes by 18 July. The swarm exhibited typical characteristics of clustered, low-to-moderate magnitude seismicity without a single dominant mainshock-aftershock pattern. Events occurred in episodic bursts, particularly on 15 July, reflecting fluid migration or stress redistribution along local fault structures within the Eastern California Shear Zone. Since 1 January 2000, 66 swarms have been recorded in the region. Notable concentrations occurred in 2019 (31 swarms) and 2020 (27 swarms), with smaller numbers in other years including two in 2022. This distribution aligns with heightened tectonic activity following the 2019 Ridgecrest Earthquake Sequence. The M 7.1 mainshock of that sequence, located 7 km from the center of swarm S20220715.1, ruptured previously unmapped faults and altered regional stress fields, contributing to subsequent swarm activity. Geologically, the Ridgecrest area lies at the boundary between the Mojave Desert and the southern Sierra Nevada, within a broad zone of distributed right-lateral shear between the Pacific and North American plates. The Little Lake Fault Zone and nearby segments of the Garlock Fault accommodate much of the deformation. Post-2019 studies have documented complex, interconnected fault networks that facilitate both large events and prolonged swarm sequences at shallow to mid-crustal depths. The 2022 swarm underscores the continued seismic productivity of the area. Monitoring such sequences provides insight into evolving fault interactions and helps refine hazard assessments for the region. Continued observation remains essential given the proximity to population centers and critical infrastructure. References
USGS Earthquake Hazards Program – Ridgecrest Earthquake Sequence documentation
California Geological Survey – Regional fault and seismicity reports
SeismoSight internal swarm classification records