Seismic Swarm S20101031.1: Analysis of Activity Near Topaz, California

Seismic swarm S20101031.1 occurred 3 km NNW of Topaz, California, beginning at 01:02 on 31 October 2010 and concluding at 13:45 on 2 November 2010. Over this 60-hour, 42-minute period, 39 earthquakes were recorded. The events clustered in a compact area characteristic of swarm sequences, where numerous earthquakes occur without a single dominant mainshock.

The sequence initiated with a magnitude 4.2 event at 5 km depth. Subsequent activity included events ranging from magnitude 0.5 to 3.0, with depths mostly between 0 and 13 km. Notable later shocks included a magnitude 3.0 event at the surface on 2 November and several magnitude 2+ events distributed across the first two days. Depths varied, with many shallow occurrences indicating activity within the upper crust.

This swarm aligns with the tectonic setting of the region, situated along the California-Nevada border in the Walker Lane belt. This zone accommodates a portion of the Pacific-North American plate boundary deformation through a network of strike-slip and normal faults. The area experiences distributed seismicity due to transtensional forces, distinct from the primary San Andreas system farther west.

Historical records indicate three prior swarms in the immediate vicinity since 2000: one each in 2000, 2003, and 2005. These earlier episodes, like the 2010 sequence, featured low-to-moderate magnitudes and short durations, consistent with fluid-driven or stress-transfer mechanisms common in the Basin and Range province.

Geological context reveals Quaternary faulting and volcanic influences nearby, including proximity to the Sierra Nevada frontal fault system. Updated regional monitoring by seismic networks confirms ongoing low-level activity, though no significant surface rupture has been associated with these swarms. Depths in the 0–13 km range match typical brittle failure zones in this extensional environment.

The 2010 swarm's temporal pattern showed peak activity within the first 12 hours, followed by a gradual decline, illustrating standard swarm decay without aftershock productivity typical of mainshock sequences. Magnitudes remained below 4.3, underscoring the modest energy release overall.

Such events provide insight into local stress accumulation and potential precursors to larger regional earthquakes, though no escalation occurred here. Continued monitoring supports refined hazard assessments for the Walker Lane transition zone.

References USGS Earthquake Hazards Program regional reports on the Walker Lane belt California Geological Survey Quaternary fault database Nevada Seismological Laboratory historical catalog summaries