Seismic Swarm S20000607.2: Analysis of Activity East of Benton, California

Seismic swarm S20000607.2 was recorded 22 km east of Benton, California, in Mono County. The sequence began at 19:27 on 6 June 2000 and concluded at 21:30 on 8 June 2000, encompassing 60 earthquakes over 50 hours and 3 minutes. This event represents the first of two swarms documented in the region since 1 January 2000. Magnitudes during the swarm ranged from -0.8 to 3.2, with the majority of events below 2.0. Depths clustered between 5 km and 12 km, indicating shallow crustal activity typical of the area. The largest event, magnitude 3.2, occurred at 18:20 on 7 June at 6 km depth. Subsequent notable shocks included multiple magnitude 2.1 events on 7 and 8 June. The swarm exhibited a rapid onset followed by a gradual decline in frequency, consistent with fluid-driven or stress-release processes in extensional settings. The location lies within the western Basin and Range Province, where active normal faulting accommodates regional extension. Nearby structures include the White Mountains fault zone and proximity to the Long Valley Caldera volcanic complex, both known for episodic seismicity. Historical records show that such swarms often occur without producing surface rupture or larger mainshock-aftershock sequences. This swarm provides insight into the distributed, low-magnitude nature of seismicity east of Benton. Most events remained under magnitude 1.5, with only a handful exceeding 2.0, underscoring the swarm's diffuse character rather than a single dominant rupture.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
California Geological Survey Regional Fault Maps
Nevada Seismological Laboratory Regional Seismicity Reports