Earthquake Swarm VS20030624.1: Geological Context and Analysis Near Volcano, Hawaii

Earthquake swarms represent clusters of seismic events occurring in rapid succession without a dominant mainshock. Swarm VS20030624.1 was recorded 5 km west-southwest of Volcano, Hawaii, beginning at 12:08 on 23 June 2003 and concluding at 08:30 on 26 June 2003. Over 68 hours and 22 minutes, 43 earthquakes were detected, with magnitudes ranging from 1.0 to 2.4 and focal depths primarily between 1 km and 13 km.

The sequence initiated with a magnitude 2.1 event at 4 km depth on 23 June. Subsequent activity included multiple events exceeding magnitude 2.0, such as the 2.3 at 10 km depth on 24 June at 05:04 and another 2.3 at 10 km on 24 June at 10:58. Depths remained shallow overall, consistent with volcanic environments, though one outlier reached 30 km on 25 June. The swarm tapered with smaller events, ending at magnitude 2.0 at 4 km depth.

This swarm aligns with the tectonic setting of the Island of Hawaii, situated above the Hawaiian hotspot. The region experiences frequent seismicity driven by magma intrusion and volcanic processes at Kilauea, one of Earth's most active volcanoes. Historical records indicate four swarms in the area since 2000, with three in 2000 and one in 2001, underscoring recurrent unrest linked to subsurface magmatic movement.

Analysis of the 43 events reveals a pattern of low-to-moderate magnitudes clustered in time, typical of fluid-induced seismicity rather than tectonic fault rupture. Depths concentrated above 13 km suggest interaction with the volcanic edifice and shallow magma pathways. Such swarms often precede or accompany surface deformation or eruptive episodes in this geologically dynamic zone.

References:
SeismoSight internal swarm classification records.
USGS Hawaiian Volcano Observatory geological summaries on Kilauea activity.