Seismic Swarm S20200527.1: Analysis of Activity Near Little Lake, California
Seismic swarm S20200527.1 occurred in a tectonically active zone of eastern California, approximately 22 km east of Little Lake in Kern County. The swarm initiated at 08:45 on 26 May 2020 and concluded at 08:42 on 30 May 2020, spanning 95 hours and 57 minutes. During this interval, 82 earthquakes were recorded, with the majority exhibiting magnitudes below 2.0 and focal depths ranging from 2 to 13 km.
The provided event catalog reveals a typical swarm pattern characterized by low-magnitude events clustered in time without a dominant mainshock. Early activity on 26 May included events such as a magnitude 1.5 at 11:04:57 (depth 5 km) and multiple magnitude 1.0 events around 13:17. Peak activity extended into 29 May, featuring the swarm's largest events: a magnitude 1.9 at 01:25:41 (depth 4 km) and a magnitude 2.0 at 09:16:09 (depth 8 km). Subsequent events on 30 May tapered off, ending with a magnitude 1.3 at 08:42:39 (depth 4 km). Negative magnitudes, indicative of microseismicity, were also documented, underscoring the swarm's microseismic nature.
This region lies within the Eastern California Shear Zone, a network of strike-slip faults accommodating Pacific-North American plate motion. Proximity to the Coso Volcanic Field contributes to elevated seismicity, driven by both tectonic stresses and hydrothermal processes. The area's volcanic history includes Pleistocene rhyolitic and basaltic eruptions, with ongoing geothermal activity influencing fluid migration that can trigger swarm sequences.
Historical data since 2000 indicate 95 swarms in the vicinity, with notable increases in frequency during 2019 (29 swarms) and 2020 (16 swarms through May). Earlier years showed lower counts, such as 7 in 2004 and 2010, reflecting episodic clustering linked to regional strain accumulation. Such patterns align with the broader seismic behavior of the Walker Lane and Garlock Fault systems, where swarms often precede or follow larger tectonic events.
The 2020 swarm's characteristics—shallow depths and rapid event succession—suggest possible involvement of pressurized fluids within fractured crust, a common mechanism in volcanically influenced terrains. No significant surface deformation or damage was associated, consistent with the low energy release.
References
- SeismoSight internal swarm classification records for S20200527.1 event parameters and historical statistics.
- USGS Earthquake Hazards Program regional tectonic summaries for the Eastern California Shear Zone and Coso Volcanic Field.