A notable earthquake swarm designated S20140605.1 occurred 146 km east-southeast of McCarthy, Alaska, from 05:38 on 5 June 2014 to 22:29 on 7 June 2014. Over 64 hours and 51 minutes, the sequence produced 123 events. The first 100 recorded shocks provide key insight into swarm dynamics in this tectonically active region.
The sequence initiated with two magnitude-5.1 events at depths of 11 km and 10 km. Subsequent activity consisted predominantly of smaller events, with magnitudes ranging from 0.5 to 2.8. Depths remained shallow, mostly between 0 km and 21 km, consistent with crustal processes. Frequency peaked in the first 12 hours, featuring numerous events below magnitude 2.0, followed by a gradual decline. Larger aftershocks, such as several magnitude-2.8 shocks, occurred intermittently but did not exceed the initial pair. This pattern reflects typical swarm behavior driven by fluid migration or stress redistribution rather than a single mainshock-aftershock cascade.
The swarm location lies within the Wrangell-St. Elias region of southern Alaska, part of the Pacific-North American plate boundary zone. Ongoing collision of the Yakutat terrane with the North American margin generates compressional stresses, crustal shortening, and elevated seismicity. The area features complex fault systems and volcanic centers, including nearby Wrangell volcanic field, where geothermal and magmatic influences can contribute to swarm triggering. Historical records document recurrent moderate seismicity here, with events often clustered due to the region's high strain rates and heterogeneous crust.
Geological context emphasizes the transition from subduction along the Aleutian megathrust to transform and collisional regimes eastward. Updated regional studies confirm persistent microseismicity and occasional swarms linked to both tectonic loading and possible hydrothermal activity. Depths observed in S20140605.1 align with the brittle upper crust, where most regional earthquakes nucleate above 20 km.
Analysis of the initial 100 events shows rapid onset followed by exponential decay in rate, with 70 percent occurring within the first day. Shallow depths and low magnitudes suggest minimal surface rupture potential, though the sequence contributed to local stress adjustments. No larger triggered events were recorded beyond the swarm window.
This activity underscores the value of dense seismic monitoring in remote Alaskan terrain for understanding plate-boundary processes. Continued observation aids hazard assessment in Wrangell-St. Elias National Park and surrounding areas.
USGS Earthquake Catalog (event parameters and regional seismicity data)
Alaska Division of Geological & Geophysical Surveys (tectonic framework reports)
SeismoSight internal swarm classification S20140605.1