Seismic Swarm VS20031211.1: Analysis of Earthquake Activity near Volcano, Hawaii

Seismic swarm VS20031211.1 occurred 5 km southwest of Volcano, Hawaii, on the Big Island. The sequence began at 18:38 on 10 December 2003 and concluded at 15:18 on 14 December 2003, spanning 92 hours and 39 minutes. During this period, 97 earthquakes were recorded, with magnitudes ranging primarily between 1.4 and 2.9 and focal depths between 1 km and 12 km.

The swarm exhibited a clustered temporal pattern, with the majority of events occurring on 11 and 12 December. Early activity on 10 December included events of magnitude 1.9 at 4 km depth and 2.1 at 12 km depth. Peak intensity developed on 11 December, featuring a magnitude 2.9 event at 2 km depth alongside numerous events around magnitude 2.0 at depths of 5–10 km. Activity gradually declined through 13 and 14 December, ending with smaller events near 1.5 magnitude at shallow depths.

This pattern aligns with typical volcanic seismic swarms in the region, where low-magnitude events often reflect magma migration or fluid pressure changes within the volcanic edifice. Depths concentrated between 4 km and 10 km suggest involvement of the shallow crustal plumbing system beneath Kilauea volcano.

The area southwest of Volcano lies on the southern flank of Kilauea, an active shield volcano formed by the Hawaiian hotspot. Kilauea’s geology features frequent intrusive activity, where magma ascends through rift zones and causes brittle failure in surrounding rock. Historical records indicate that such swarms commonly precede or accompany eruptive episodes or dike intrusions along the East Rift Zone and Southwest Rift Zone.

Since 1 January 2000, eleven swarms have been documented in this locale. The distribution includes three in 2000, one in 2001, and seven in 2003, underscoring elevated seismic productivity during that interval. These events illustrate the persistent volcanic-tectonic interaction characteristic of Hawaii’s young oceanic island setting.

Insights from the swarm data reveal a predominance of events with magnitudes below 2.2, consistent with microseismicity driven by hydrothermal or magmatic processes rather than large tectonic release. The relatively shallow depths and tight spatial clustering point to localized stress perturbations within the volcanic crust. Such sequences provide valuable indicators for monitoring magma movement and assessing short-term volcanic hazards in the Kilauea region.

References SeismoSight internal classification records for swarm VS20031211.1 USGS Hawaiian Volcano Observatory volcanic activity summaries Global Volcanism Program database entries for Kilauea Hawaii State geological survey reports on rift zone seismicity