Seismic Swarm VS20120223.1 Near Volcano, Hawaii: February 2012 Event Analysis

Seismic swarm VS20120223.1 was recorded in the region 10 km west-southwest of Volcano, Hawaii, on the Big Island. The sequence began at 11:17 on 22 February 2012 and concluded at 16:03 on 25 February 2012, encompassing a total duration of 76 hours and 45 minutes during which 80 earthquakes were detected.

This swarm occurred within the tectonically active Hawaiian volcanic system, where the island chain sits above a mantle hotspot that fuels ongoing shield-volcano growth. The location places the events on the southwestern flank of Kīlauea, one of the world's most active volcanoes. Shallow crustal stresses in this area frequently produce earthquake swarms linked to magma intrusion, dike propagation, and gravitational adjustments along rift zones.

Event magnitudes ranged primarily between 0.5 and 4.3, with the majority falling between 1.5 and 2.5. Notable larger events included a magnitude 4.1 earthquake at 07:02 on 24 February at 4 km depth and a magnitude 4.3 event at 13:52 the same day at 5 km depth. Depths were predominantly shallow, concentrated between 1 and 5 km, consistent with volcanic-tectonic activity; one outlier reached 27 km. The sequence showed clustered activity on 22 and 24 February, with reduced rates on 23 and 25 February before termination.

Such swarms reflect the dynamic interplay between magmatic processes and regional faulting in the Hawaiian hotspot setting. Historical records maintained by SeismoSight indicate 31 swarms have occurred in the same area since 1 January 2000. Yearly distribution includes three swarms in 2000, one in 2001, eight in 2003, eight in 2004, one in 2005, two in 2006, four in 2007, one in 2008, and three in 2011. These recurrent episodes underscore the persistent seismic character of the Kīlauea southwest flank driven by volcanic inflation and rift-zone extension.

Analysis of the 2012 swarm highlights typical patterns of volcanic seismicity in Hawaii, where low-to-moderate magnitude events cluster over days without necessarily leading to surface eruption. The data align with long-term monitoring observations that link swarm duration and energy release to subsurface magma movement.

References

SeismoSight internal swarm classification database
USGS Hawaiian Volcano Observatory geological summaries on Kīlauea activity