Seismic Swarm VS20041214.1 Near Volcano, Hawaii

An earthquake swarm designated VS20041214.1 occurred 7 km southwest of Volcano, Hawaii, from 00:08 on 14 December 2004 to 00:47 on 15 December 2004. During this 24-hour and 38-minute period, 32 earthquakes were recorded. Magnitudes ranged from 1.0 to 2.3, with the majority falling between 1.4 and 2.2. Depths varied from 1 km to 16 km, clustering primarily between 5 km and 14 km. Notable events included a magnitude 2.3 quake at 11:29 on 14 December at 8 km depth and another magnitude 2.3 event at 17:22 the same day at 11 km depth. Shallower activity, such as the magnitude 1.3 event at 1 km depth around 14:28, interspersed with deeper occurrences, suggesting localized stress adjustments within the volcanic subsurface.

Analysis of the swarm reveals a temporal pattern of increasing frequency in the afternoon and evening of 14 December, followed by a decline toward the swarm's conclusion. Depths indicate activity spanning both shallow crustal levels and mid-crustal zones, consistent with fluid migration or minor fault slip in a volcanically active setting. No single dominant magnitude trend emerged, reflecting the typical diffuse nature of swarm sequences rather than a mainshock-aftershock progression.

This event fits into broader seismic patterns on the Island of Hawaii. Since 1 January 2000, 15 such swarms have been documented in the region. Yearly distribution shows three swarms in 2000, one in 2001, eight in 2003, and three in 2004, underscoring episodic seismic unrest tied to the island's dynamic geology.

The area southwest of Volcano lies on the flanks of Kilauea volcano within Hawaii Volcanoes National Park. Hawaii's geology stems from the Hawaiian hotspot, a mantle plume that has generated the Hawaiian-Emperor seamount chain over approximately 80 million years. The Big Island represents the youngest and most volcanically active portion, with Kilauea exhibiting near-continuous activity for centuries. Earthquake swarms here commonly arise from magma movement, dike intrusions, or adjustments along rift zones and faults associated with volcanic loading. Depths observed in the 2004 swarm align with known brittle-ductile transition zones beneath the volcano, typically 3–15 km.

Historical context includes major eruptive periods at Kilauea, such as the prolonged Puʻuʻōʻō eruption from 1983 to 2018, which featured numerous seismic swarms linked to magma transport. The 2004 swarm occurred during a phase of summit and rift zone inflation, illustrating how such sequences contribute to monitoring volcanic hazards. Updated assessments from the Hawaiian Volcano Observatory emphasize ongoing surveillance of these patterns to forecast potential eruptive activity.

References: USGS Earthquake Catalog Hawaii Volcano Observatory annual reports Geological Society of America publications on Hawaiian volcanism