Seismic Swarm S20200219.2 Near Ridgecrest, California

Earthquake swarm S20200219.2 occurred approximately 22 km north of Ridgecrest in Kern County, California. The sequence initiated at 15:40 UTC on 18 February 2020 and concluded at 20:18 UTC on 21 February 2020, spanning 76 hours and 37 minutes. During this period, 87 earthquakes were recorded.

The swarm exhibited typical characteristics of low-magnitude clustered seismicity. Event magnitudes ranged from negative values to a peak of 2.7, with the majority below 1.0. Focal depths concentrated between 3 km and 10 km, consistent with shallow crustal activity in the region. Notable events included a magnitude 2.3 earthquake at 17:59 UTC on 18 February and a magnitude 2.7 event at 07:12 UTC on 20 February. Activity showed episodic clustering rather than a single mainshock-aftershock pattern.

This swarm took place within the Eastern California Shear Zone, a broad region of distributed right-lateral strike-slip faulting that accommodates a portion of the Pacific-North America plate motion. The area lies near the intersection of the Garlock Fault and the Little Lake Fault Zone. These structures have produced multiple moderate earthquakes historically, including the 2019 Ridgecrest sequence of magnitude 6.4 and 7.1 events located roughly 20–30 km to the south.

Seismic swarms are recurrent in this portion of the Mojave Desert. Records since 2000 document 85 such sequences, with notable annual counts including four in 2000, seven in 2004, seven in 2010, thirty in 2019, and four in 2020. The elevated swarm frequency observed in 2019 aligns with elevated background seismicity following the Ridgecrest mainshocks, suggesting possible triggering or stress redistribution effects.

The 2020 swarm did not produce felt shaking at the surface or reported damage, reflecting the small magnitudes involved. Such sequences contribute to ongoing monitoring of fault interaction and strain accumulation along secondary structures north of Ridgecrest.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
California Geological Survey regional fault maps
Southern California Earthquake Data Center swarm records