Seismic Swarm VS20150224.1: February 2015 Activity Southwest of Volcano, Hawaii

Seismic swarm VS20150224.1 was recorded 10 km southwest of Volcano, Hawaii, on the Big Island. The sequence began at 20:03 on 23 February 2015 and concluded at 13:08 on 27 February 2015, spanning 89 hours and 5 minutes. During this interval, 72 earthquakes were registered. Magnitudes ranged from 0.8 to 2.7, with the majority between 1.5 and 2.4. Focal depths were predominantly shallow, concentrated between 0 and 11 km, consistent with crustal processes in the volcanic edifice.

Activity commenced with a magnitude 1.2 event at 1 km depth. The following day featured the highest event rate, including several magnitude 2+ shocks at depths of 7–10 km. Notable events included a magnitude 2.7 earthquake at 8 km depth on 24 February at 21:22 and paired magnitude 2.4 events later that evening. Activity declined steadily through 25–27 February, ending with a magnitude 1.4 event at 2 km depth. The temporal clustering and shallow depths suggest fluid migration or minor stress adjustments within the volcanic system rather than a single large rupture.

This swarm occurred in a region shaped by the Hawaiian hotspot, which has generated the Hawaiian-Emperor seamount chain over tens of millions of years. The Big Island hosts active shield volcanoes, including Kilauea and Mauna Loa, built by repeated basaltic eruptions. Kilauea, located near the swarm epicentral area, remains one of Earth’s most active volcanoes, with documented summit and rift-zone activity driven by magma supply from a hotspot source approximately 60 km beneath the surface. Seismic swarms in this setting commonly reflect dike propagation, pressure changes in shallow magma reservoirs, or fault slip induced by volcanic loading.

Historical records indicate 36 swarms in the same region since 1 January 2000. Yearly distribution shows elevated rates in 2003 (8 swarms) and 2004 (6 swarms), followed by lower but recurrent activity in 2011–2014. These episodes align with known periods of heightened volcanic unrest at Kilauea, underscoring the persistent influence of magmatic and tectonic stresses on local seismicity.

The February 2015 swarm fits within this pattern of short-duration, low-magnitude sequences that rarely exceed magnitude 3 yet provide valuable indicators of subsurface conditions. Depths mostly shallower than 11 km place events within the volcanic crust, where interactions between magma, groundwater, and pre-existing faults are frequent. No escalation to significant eruptive activity was associated with this particular sequence.

Continued monitoring by the Hawaiian Volcano Observatory supports improved forecasting of unrest. Integration of seismic, geodetic, and gas data helps distinguish swarms linked to magma movement from those driven primarily by tectonic stress release.

References
SeismoSight internal classification for swarm VS20150224.1
USGS Hawaiian Volcano Observatory volcano and earthquake catalogs
USGS Earthquake Hazards Program event data for Hawaii region