The 2003 Earthquake Swarm Near Mina, Nevada: Characteristics and Regional Context

An earthquake swarm designated S20030529.1 was recorded 24 km southeast of Mina, Nevada, beginning at 02:14 on 29 May 2003 and concluding at 10:10 on 2 June 2003. Over 103 hours and 55 minutes, the sequence produced 164 events. Analysis of the first 100 recorded earthquakes reveals predominantly low-magnitude activity with shallow focal depths, consistent with swarm behavior rather than a mainshock-aftershock sequence.

The events exhibited magnitudes ranging from 0.5 to 4.0, with the largest shock reaching magnitude 4.0 at 22:52 on 29 May. Depths were concentrated between 0 and 9 km, though isolated events extended to 16 km. Timing showed clustering during the afternoon and evening of 29 May, followed by continued but diminishing activity through 30 May. No single dominant event triggered the sequence; instead, energy release occurred through numerous small shocks distributed across the period.

Western Nevada lies within the Basin and Range Province, where crustal extension has produced north-trending normal faults since the Miocene. The Mina region specifically occupies a transition zone between the Walker Lane belt to the west and the Central Nevada Seismic Belt to the east. The Walker Lane accommodates approximately 20 percent of Pacific-North America relative plate motion through right-lateral shear and associated normal faulting. This tectonic setting generates frequent seismic swarms, often linked to fluid migration or aseismic slip on favorably oriented faults.

Historical records document multiple swarms and moderate earthquakes in Mineral County and adjacent areas. Notable activity includes the 1932 Cedar Mountain earthquake (M 7.2) roughly 80 km northeast and recurrent small-magnitude clusters near the Mina deflection. Instrumental monitoring since the late twentieth century confirms elevated background seismicity rates compared with the stable interior of the continent. Updated catalogs from regional networks show that swarm-type sequences remain common, with no significant change in long-term rates through 2023.

The 2003 swarm fits established patterns of shallow, low-magnitude activity in this extensional regime. Event depths align with the seismogenic zone documented for the region, typically limited to the upper 15 km of crust. The absence of a clear magnitude-frequency rollover at higher magnitudes during the first 100 events suggests the sequence did not exhaust local strain capacity. Such swarms contribute to hazard assessments by illustrating distributed deformation away from major mapped faults.

Ongoing geodetic measurements indicate continued extension across the Walker Lane at rates of several millimeters per year. Integration of seismic and geodetic data supports models in which swarms represent transient adjustments within a broader shear zone. Continued monitoring by the Nevada Seismological Laboratory and the U.S. Geological Survey maintains the catalog essential for refining these interpretations.

References

U.S. Geological Survey Earthquake Catalog
Nevada Seismological Laboratory Regional Seismicity Reports
Dixon et al., Tectonic Setting of the Walker Lane, Geological Society of America Special Papers (updated summaries through 2023)