Seismic Swarm VS20030805.1: Earthquake Activity Southwest of Volcano, Hawaii

Seismic swarm VS20030805.1 was recorded 12 km southwest of Volcano, Hawaii, on the Big Island. The sequence began at 06:11 on 4 August 2003 and concluded at 04:12 on 6 August 2003, spanning 46 hours and encompassing 31 earthquakes.

The Hawaiian Islands owe their existence to the Hawaiian hotspot, a mantle plume that has generated the archipelago over millions of years. The swarm location lies on the southwestern flank of Kīlauea volcano, one of the world’s most active shield volcanoes. Kīlauea’s frequent magma intrusions and flank movements generate abundant shallow seismicity. Earthquakes in this region typically result from stress changes induced by magma migration, dike propagation, or gravitational adjustments along the volcano’s south flank.

The 2003 swarm exhibited low to moderate magnitudes between 1.1 and 2.1. Focal depths ranged from 2 km to 13 km, consistent with activity in the shallow volcanic crust and upper volcanic edifice. The sequence displayed temporal clustering, with the highest event rate occurring late on 4 August 2003 when multiple events occurred within minutes. Magnitudes remained modest throughout, indicating brittle failure on small faults without escalation to larger ruptures.

Subsequent events on 5 August maintained similar characteristics, with isolated peaks at 00:10 and 00:24. Activity declined sharply after 06:00 on 5 August before a final event at 04:12 on 6 August. No surface deformation or eruptive phenomena were associated with this particular swarm according to the provided classification.

Since 1 January 2000, seven swarms have been documented in the same general area. Earlier episodes occurred in 2000 (three swarms), 2001 (one swarm), and 2003 (three swarms, including the present sequence). Such recurrent swarms reflect the ongoing volcanic-tectonic interaction that characterizes Kīlauea’s dynamic environment.

This swarm illustrates typical background seismicity driven by the interplay between magmatic processes and flank instability. Continued monitoring by the Hawaiian Volcano Observatory remains essential for distinguishing routine swarms from those that may precede significant eruptive or intrusive events.

References

SeismoSight internal swarm classification VS20030805.1
USGS Hawaiian Volcano Observatory geological summaries
USGS Earthquake Hazards Program regional tectonics reports