Seismic Swarm VS20030715.1: Analysis of Activity Southwest of Volcano, Hawaii

A notable seismic swarm, designated VS20030715.1, occurred 8 km southwest of Volcano, Hawaii, from 04:39 on 15 July 2003 to 11:05 on 16 July 2003. Over 30 hours and 26 minutes, the event registered 31 earthquakes, providing valuable data on subsurface dynamics in this volcanically active zone.

The swarm's sequence began with a magnitude 1.3 event at 10 km depth. Subsequent activity included multiple events clustered at shallow depths of 1–10 km, with magnitudes ranging from 1.1 to 2.1. Notable occurrences featured a 2.1-magnitude quake at 1 km depth early on 15 July, followed by several 1.6–1.9 magnitude events at depths of 6–15 km throughout the evening. Activity tapered with smaller events, including a final 1.2-magnitude quake at 4 km depth on 16 July. Depths varied from near-surface (1 km) to moderate (29 km), reflecting both shallow crustal adjustments and deeper magmatic influences.

This region lies on the Big Island of Hawaii, dominated by Kilauea volcano, one of Earth's most active shield volcanoes. Kilauea's flank experiences frequent seismicity due to magma intrusion, rift zone extension, and gravitational spreading of the volcanic edifice. The southwest location aligns with the Kilauea Southwest Rift Zone, where historical eruptions and ground deformation are common. Earthquake swarms here typically signal fluid migration or pressure changes within the volcanic system rather than tectonic faulting alone.

Hawaii's volcanic geology stems from the Hawaiian hotspot, with the Pacific plate moving over a mantle plume. Kilauea has erupted continuously since 1983, shaping landscapes through lava flows and caldera activity. Seismic monitoring by agencies such as the USGS Hawaiian Volcano Observatory has documented similar swarms as precursors or companions to eruptive phases, underscoring the area's dynamic nature.

Historical records indicate six swarms in the region since 1 January 2000. Earlier events occurred in 2000 (three swarms), 2001 (one swarm), and 2003 (two swarms, including VS20030715.1). These patterns suggest recurring subsurface processes tied to Kilauea's ongoing activity.

Insights from the swarm reveal a predominance of low-magnitude events (mostly 1.1–2.1) at shallow to intermediate depths, consistent with magma-related fracturing. The 30-hour duration and 31 events indicate a moderate-intensity episode, likely driven by localized pressure release without leading to surface eruption. Such data enhance understanding of swarm evolution in hotspot volcanic settings.

References

USGS Hawaiian Volcano Observatory reports on Kilauea seismicity and rift zone geology (updated through 2023 data archives).
Hawaii Volcanoes National Park geological summaries on volcanic history and monitoring.
SeismoSight internal classification records for swarm VS20030715.1 parameters.