Analysis of the VS20041215.1 Earthquake Swarm in Hawaii

The VS20041215.1 swarm represents a notable seismic episode recorded in the region 27 km east of Honaunau-Napoopoo on Hawaii’s Big Island. Activity commenced at 14:49 on 14 December 2004 and concluded at 01:11 on 30 December 2004, spanning 370 hours and 22 minutes. During this interval, 342 earthquakes were registered, providing a concentrated dataset for examining subsurface processes beneath the island’s southwestern flank.

Hawaii’s geology is shaped by hotspot volcanism, with the Big Island formed by the coalescence of five shield volcanoes. Kīlauea and Mauna Loa dominate current activity, while Hualālai and Mauna Kea contribute to the regional stress field. The swarm location lies along the southern flank, where volcanic loading and gravitational spreading interact with the underlying oceanic crust and mantle. Earthquakes in this setting commonly arise from magma migration, fault slip on décollement surfaces, and flexure of the lithosphere.

The first 100 events of the swarm displayed magnitudes between 1.3 and 2.6 and focal depths predominantly between 30 km and 50 km. These depths place the activity below the typical volcanic edifice, suggesting involvement of the lower crust or uppermost mantle. The temporal distribution showed an initial peak within the first 48 hours, followed by a gradual decline, consistent with fluid-driven triggering or stress diffusion rather than a single mainshock-aftershock sequence.

Regional historical records indicate that earthquake swarms have occurred intermittently since systematic monitoring began. Since 1 January 2000, three swarms have been documented, with VS20041215.1 identified as the earliest. Subsequent episodes reflect the persistent influence of magmatic and tectonic forces on the island’s southern sector.

The swarm’s characteristics align with known patterns of deep seismicity associated with magma transport beneath the Kīlauea and Mauna Loa systems. Such events contribute to long-term monitoring of volcanic unrest and help refine models of flank stability. Continued observation of similar sequences supports improved hazard assessment for communities on the island’s western and southern coasts.

References

United States Geological Survey, Hawaiian Volcano Observatory seismic catalogs (2000–2024).
Hawaii State Earthquake Database, swarm classification records.
SeismoSight internal swarm registry, VS20041215.1 parameters.