Seismic Swarm S20050918.1 Near Incline Village, Nevada

Seismic swarm S20050918.1 was recorded 10 km north-northeast of Incline Village, Nevada, on the northern shore of Lake Tahoe. The sequence began at 22:56 UTC on 17 September 2005 and concluded at 12:41 UTC on 20 September 2005, spanning 61 hours and 44 minutes. During this interval, 34 earthquakes were detected, with magnitudes ranging from –0.1 to 2.2 and focal depths between 3 km and 13 km.

The swarm initiated with a magnitude 2.2 event at 10 km depth. Subsequent activity consisted predominantly of micro-earthquakes below magnitude 1.0, interspersed with a few events reaching magnitude 1.4–1.5. Notable shocks included a magnitude 1.4 at 01:25 on 18 September (8 km depth), another magnitude 1.4 at 08:32 the same day (8 km depth), and a magnitude 1.5 at 20:27 on 19 September (8 km depth). Depths clustered most frequently between 5 km and 8 km, consistent with shallow crustal faulting in the region.

This swarm fits into a broader pattern of seismic activity in the Tahoe-Truckee area. Since 1 January 2000, seven swarms have occurred in the vicinity. Earlier episodes were documented in 2003 (three swarms), 2004 (two swarms), and 2005 (two swarms, including the present sequence).

The Incline Village area lies within the northern Walker Lane belt, a zone of distributed right-lateral shear accommodating approximately 10–15 mm per year of Pacific–North America plate motion. The belt separates the rigid Sierra Nevada block from the extending Basin and Range province. Active faults in the region include strands of the North Tahoe fault and the Incline Village fault, which exhibit both normal and strike-slip components. Seismicity is driven by this transtensional regime rather than magmatic processes, although fluid migration along faults may contribute to swarm behavior.

Historical records indicate that the Lake Tahoe basin has experienced recurrent moderate earthquakes, including the 1966 Truckee event (M 6.0) located roughly 30 km to the northeast. Paleoseismic studies document Holocene surface rupture on nearby faults, underscoring the potential for larger events despite the predominance of small-magnitude swarms in recent decades.

The 2005 swarm produced no reported damage or felt shaking beyond the immediate epicentral area, consistent with the modest magnitudes involved. Continued monitoring by regional seismic networks remains essential for characterizing long-term strain accumulation along Walker Lane structures.

References

• USGS Earthquake Catalog (queried for 2000–2024 events near Incline Village, NV)
• Nevada Seismological Laboratory, University of Nevada, Reno – regional fault and swarm summaries
• Faulds, J.E., et al. (2005), “Kinematics and timing of strike-slip and normal faulting in the northern Walker Lane,” Geological Society of America Special Paper 434