Earthquake Swarm VS20201130.1: Seismic Activity on Hawai'i Island

An earthquake swarm designated VS20201130.1 was recorded on the Island of Hawai'i between 18:22 on 29 November 2020 and 19:14 on 30 November 2020. Over this 24-hour-and-52-minute period, 88 earthquakes were detected. The events were concentrated in a region of active volcanism, with magnitudes ranging from 0.4 to 3.2 and focal depths predominantly between 0 and 4 km. The largest event reached magnitude 3.2 at a depth of 0 km, occurring at 12:06 on 30 November. Multiple events clustered around magnitudes 1.8–2.2, reflecting typical swarm characteristics of numerous small, closely spaced shocks without a single dominant mainshock.

Shallow depths indicate activity within or near the volcanic edifice, consistent with magma migration or fluid movement in the subsurface. The temporal distribution showed an initial pair of events at 18:22 on 29 November, followed by a steady sequence through the night and into the following afternoon, with the final recorded shock at 19:14 on 30 November. Such swarms arise from stress changes induced by volcanic processes rather than tectonic fault rupture.

Hawai'i Island lies above the Hawaiian hotspot, where the Pacific plate moves over a mantle plume, sustaining shield volcanoes including Kīlauea and Mauna Loa. These volcanoes produce frequent seismic swarms linked to dike intrusions, summit inflation, and rift-zone extension. Historical records document persistent low-level seismicity punctuated by episodic swarms, reflecting the dynamic interplay between magma supply and crustal stress. Since 1 January 2000, 64 swarms have been identified on the island, distributed across years as follows: 2000 (3), 2001 (1), 2003 (8), 2004 (5), 2005 (1), 2006 (2), 2007 (4), 2008 (1), 2011 (3), 2012 (4), 2013 (1), 2014 (2), 2015 (3), 2016 (2), 2017 (2), 2018 (9), 2019 (3), and 2020 (10). Elevated swarm counts in 2003, 2018, and 2020 correlate with documented eruptive or intrusive episodes at Kīlauea.

This swarm fits the established pattern of short-duration, high-frequency microseismicity that precedes or accompanies volcanic unrest. Depths near or above sea level suggest involvement of the shallow volcanic system, where pore-pressure changes can trigger rapid sequences of small events. Monitoring networks operated by the U.S. Geological Survey Hawaiian Volcano Observatory provide continuous data that enable precise location and magnitude determination for such activity.

Continued observation of swarm statistics contributes to refined hazard assessments for the island's populated districts and infrastructure. Patterns observed since 2000 underscore the recurrent nature of these episodes within Hawai'i's volcanic environment.

References

SeismoSight internal swarm classification database
USGS Hawaiian Volcano Observatory seismic monitoring reports