Seismic Swarm S20240811.1: Analysis of Activity East of Little Lake, California

Seismic swarm S20240811.1 was recorded 20 km east of Little Lake in Inyo County, California. The sequence began at 16:41 on 10 August 2024 and concluded at 09:25 on 16 August 2024, spanning 136 hours and 43 minutes. During this interval, 78 earthquakes were detected, with magnitudes ranging from negative values to a peak of 3.7.

The largest event, magnitude 3.7, occurred at 09:45 on 11 August at a depth of 5 km. Subsequent notable shocks included magnitudes of 2.8, 2.7, 2.6 (two events), 2.4, and 2.2 (two events). Depths were predominantly shallow, clustered between 2 km and 8 km, consistent with activity in the upper crust. Many events registered below magnitude 1.0, reflecting the high sensitivity of modern monitoring networks in capturing microseismicity.

This swarm fits established patterns in the region. The area lies within the Eastern California Shear Zone, a tectonically active belt characterized by distributed right-lateral strike-slip faulting and north-northwest trending normal faults. These structures accommodate a portion of the Pacific-North American plate boundary deformation. The Coso Volcanic Field, located nearby, contributes to elevated geothermal gradients and fluid-driven seismicity, where pressurized fluids can trigger episodic earthquake clusters without a single dominant mainshock-aftershock sequence.

Historical records since 2000 document 118 swarms in the same locale. Annual counts show variability, with notable peaks in 2019 (31 swarms) and 2020 (24 swarms), followed by lower activity in subsequent years. The 2024 swarm represents the first recorded event of this type in the current year. Such recurrent swarms underscore the persistent strain accumulation and release along local fault networks.

Swarm characteristics typically include rapid onset, spatial clustering, and a broad magnitude distribution without clear foreshock-mainshock-aftershock progression. Depths in the present sequence align with previous observations, remaining above 10 km and often concentrated near 4–5 km. This distribution suggests involvement of shallow crustal faults influenced by both tectonic stress and hydrothermal processes.

Ongoing monitoring by regional seismic networks continues to track after-activity and potential migration of events. The shallow nature of the recorded earthquakes indicates limited potential for significant surface rupture, though felt reports may occur near the epicentral area for events above magnitude 3.0.

References

SeismoSight internal swarm classification and event catalog.
USGS Earthquake Hazards Program regional tectonic summaries.
California Geological Survey fault and seismic activity reports.