Seismic Swarm S20181130.1 Near Little Lake, California

Seismic swarm S20181130.1 occurred approximately 12 km northeast of Little Lake in Inyo County, California. The sequence began at 19:22 on 29 November 2018 and concluded at 13:16 on 2 December 2018, spanning 65 hours and 53 minutes. During this period, 51 earthquakes were recorded, with magnitudes ranging from 0.2 to 2.5 and focal depths predominantly between 1 and 2 km.

The swarm exhibited typical characteristics of clustered microseismicity, featuring numerous low-magnitude events without a dominant mainshock. The largest event reached magnitude 2.5 at 22:37 on 29 November at a depth of 1 km. Multiple events clustered in the initial hours, followed by episodic activity that gradually declined. Such patterns are consistent with fluid migration or stress adjustments along local fault structures in the Eastern California Shear Zone.

This region lies within a tectonically active corridor marked by right-lateral strike-slip faulting and distributed deformation. Proximity to the Coso Volcanic Field introduces potential geothermal and magmatic influences that can modulate swarm behavior through pore-pressure changes. Historical records indicate recurrent swarms in the area, reflecting ongoing tectonic and possibly hydrothermal processes.

Since 1 January 2000, 52 swarms have been documented in the vicinity. Annual counts include four in 2000, four in 2001, two in 2002, seven in 2004, one in 2005, six in 2006, one in 2009, seven in 2010, one in 2011, four in 2012, four in 2013, two in 2014, three in 2015, four in 2016, and two in 2017. These episodes underscore the persistent seismic productivity of the Little Lake–Coso corridor.

The shallow depths observed in swarm S20181130.1 align with patterns seen in prior events, suggesting activation of near-surface fractures. No damage or felt reports were associated with this sequence, consistent with its modest magnitudes. Continued monitoring remains essential given the area's history of swarm activity and its location within a major shear zone.

References

SeismoSight internal swarm classification database.
USGS Earthquake Catalog (regional tectonic framework).
California Geological Survey (Eastern California Shear Zone geology).