Seismic Swarm S20090109.1 Near Indian Springs, Nevada

Seismic swarm S20090109.1 occurred approximately 46 km west-northwest of Indian Springs, Nevada, between 18:53 UTC on 8 January 2009 and 12:30 UTC on 12 January 2009. Over this 89-hour period, 48 earthquakes were recorded, with magnitudes ranging from -0.5 to 2.1 and focal depths between 0 and 10 km. The sequence consisted predominantly of microearthquakes, including numerous events below magnitude 0.0, interspersed with a few events reaching low-positive magnitudes. The largest shock measured 2.1 on 9 January at 11:28 UTC at a depth of 4 km. Activity was most intense during the first two days, after which event rates declined steadily until termination on 12 January.

The temporal distribution showed clustering, with many events occurring within minutes of one another on 9 January. Depths remained shallow throughout, consistent with brittle failure in the upper crust. No events exceeded magnitude 3.0, indicating a low-energy swarm rather than a mainshock-aftershock sequence.

The swarm took place in southern Nevada within the Basin and Range Province, a region undergoing active crustal extension driven by Pacific-North American plate interaction. This tectonic setting produces numerous normal faults that accommodate east-west stretching. The area near Indian Springs lies along the southern margin of the Walker Lane belt, where right-lateral shear and extension create favorable conditions for episodic swarm activity. Historical records indicate that 26 swarms have occurred in the vicinity since 1 January 2000, with notable clusters in 2000 (5 swarms), 2002 (7), 2008 (7), and smaller numbers in intervening years.

Such swarms are common in the Great Basin and are often attributed to fluid migration along faults or transient stress changes rather than magmatic intrusion. The shallow depths observed align with the typical seismogenic zone in this part of Nevada, where brittle failure occurs above approximately 10–12 km. Regional fault systems, including segments of the Rock Valley and Cane Spring faults, have been associated with past microseismicity, although specific causative structures for the 2009 swarm remain undetermined from catalog data alone.

Long-term monitoring by regional networks has documented that swarm episodes in southern Nevada rarely produce damaging ground motion. The 2009 sequence remained well below thresholds for felt reports or infrastructure impact. Continued surveillance contributes to refined understanding of strain accumulation and release along the plate-boundary transition zone.

References

• Nevada Seismological Laboratory earthquake catalog
• USGS Earthquake Hazards Program regional seismicity reports
• USGS Geological Survey Professional Paper series on Basin and Range tectonics