Seismic Swarm S20200708.3: Activity Near Little Lake, California

Seismic swarm S20200708.3 was recorded in the region 19 km east of Little Lake, California. The sequence began at 16:01 on 7 July 2020 and concluded at 01:03 on 21 July 2020, spanning 321 hours and 2 minutes. A total of 239 earthquakes were detected during this period.

Analysis of the initial events reveals predominantly low-magnitude activity. Magnitudes ranged from negative values to a maximum of 2.0, with the majority falling between 0.0 and 1.5. Focal depths varied between 2 km and 12 km, indicating shallow crustal seismicity consistent with regional fault structures. Early events on 7 July clustered around magnitudes of 0.3–1.3 at depths of 4–11 km. Subsequent activity through 12 July maintained similar characteristics, with occasional spikes to magnitude 1.5 but no escalation to larger events within the first 100 recorded shocks.

This swarm occurred within the Eastern California Shear Zone, a tectonically active belt accommodating right-lateral shear between the Pacific and North American plates. The area features distributed strike-slip faulting, including segments associated with the Little Lake Fault and nearby structures. Seismicity here reflects ongoing strain accumulation and release along these faults.

Historical data indicate frequent swarm activity in the region since 2000, with 88 swarms documented through 2020. Annual counts show variability, including peaks of 31 swarms in 2019 and 20 in 2020, alongside lower activity in earlier years such as 2001 (1 swarm) and 2014 (1 swarm). These swarms typically involve numerous small events without a dominant mainshock.

The 2019 Ridgecrest earthquake sequence, featuring a magnitude 7.1 event on 6 July located 8 km from the swarm center, underscores the area's capacity for significant ruptures. That sequence activated multiple fault segments and altered local stress conditions, potentially influencing subsequent swarm behavior.

Ongoing monitoring in this zone supports improved understanding of swarm dynamics and their relation to larger tectonic processes. Continued observation aids in assessing seismic hazard for nearby communities and infrastructure.

References

• SeismoSight internal swarm classification records (S20200708.3 parameters and event data)
• USGS Earthquake Catalog (regional historical seismicity and Ridgecrest sequence details)