Seismic Swarm S20190415.1 Near Round Valley, California
A seismic swarm designated S20190415.1 occurred 6 km east-southeast of Round Valley in Inyo County, California. The sequence began at 12:11 on 15 April 2019 and concluded at 15:01 on 16 April 2019, lasting 26 hours and 49 minutes. During this period, 64 earthquakes were recorded.
The events exhibited magnitudes between 0.6 and 3.8, with focal depths ranging from 6 km to 10 km. The largest shock reached magnitude 3.8 at 17:55 on 15 April at a depth of 9 km. Other notable events included a magnitude 3.2 at 15:58 and several magnitude 2.1–2.8 shocks distributed throughout the first day. Smaller events dominated the later stages, with the final recorded earthquake of magnitude 1.7 occurring at 15:01 on 16 April.
Round Valley lies along the eastern flank of the Sierra Nevada in the Basin and Range province. This tectonically active region experiences ongoing extension driven by Pacific–North American plate interaction. Normal faulting along the Sierra Nevada frontal fault system and subsidiary structures accommodates much of the regional strain. Earthquake swarms in this setting often reflect fluid migration or aseismic slip that perturbs nearby fault segments without producing a single dominant mainshock.
The 2019 swarm fits a pattern of episodic seismic activity documented in the area. Since 1 January 2000, six swarms have occurred near Round Valley, with prior episodes in 2003 (one swarm), 2007 (two swarms), 2012 (two swarms), and 2016 (one swarm). Such recurrent swarms suggest persistent but distributed strain release along immature fault networks rather than long-term locking of a major through-going structure.
No surface rupture or significant damage was associated with S20190415.1. The shallow depths and moderate magnitudes are typical for background seismicity in the Owens Valley region, which has hosted larger historical events, including the 1872 Owens Valley earthquake. Continued monitoring remains essential for distinguishing swarm behavior from potential foreshock sequences in this extensional tectonic environment.