Seismic Swarm Near Warm River, Idaho: February 2020 Event and Regional Context

On February 12, 2020, a seismic swarm designated SVS20200212.1 was recorded 46 km east-northeast of Warm River, Idaho. The sequence began at 03:07 UTC and concluded at 14:42 UTC, spanning 11 hours and 34 minutes. During this interval, 36 earthquakes were detected, with magnitudes ranging from 0.6 to 2.2 and focal depths between 1 and 4 km. All events remained shallow, consistent with activity driven by fluid movement or minor crustal adjustments in the region.

The swarm exhibited a typical pattern of clustered, low-magnitude events without a dominant mainshock. Initial activity included events of magnitude 1.7 and 2.0 within the first five minutes, followed by intermittent bursts peaking around 05:15 UTC with a magnitude 2.2 shock. Later events tapered off, ending with a magnitude 0.9 quake. Such sequences often reflect episodic stress release rather than progressive rupture along a single fault.

This event aligns with historical patterns in the area. Since 2000, 15 swarms have occurred near Warm River, distributed across years including 2002 (four swarms), 2006 (two), 2008 (one), 2009 (three), 2012 (one), 2013 (one), 2015 (one), 2016 (one), and 2019 (one). These recurrent episodes indicate persistent underlying conditions favoring swarm-type seismicity.

Geologically, the location lies within the northeastern Basin and Range province, adjacent to the Snake River Plain and influenced by the Yellowstone hotspot. The hotspot has driven volcanism and crustal deformation for millions of years, creating a network of normal faults and volcanic features. Shallow seismicity frequently arises from hydrothermal fluid circulation or minor magmatic intrusions interacting with pre-existing fractures. Depths of 1–4 km place events within the brittle upper crust, where such interactions are common.

The broader Intermountain Seismic Belt, extending through eastern Idaho, experiences background seismicity tied to extensional tectonics. While larger events have occurred regionally in past decades, swarms like this one contribute to ongoing strain accommodation without producing significant surface rupture. Monitoring by regional networks continues to track these patterns for improved hazard assessment.

References
USGS Earthquake Catalog (earthquake.usgs.gov)
Idaho Geological Survey regional reports
Yellowstone Volcano Observatory updates on hotspot-related seismicity