Seismic Swarm VS20231202.1: Analysis of Recent Activity on Hawaiʻi Island

A seismic swarm designated VS20231202.1 was recorded on the Island of Hawaiʻi between 13:31 UTC on 1 December 2023 and 19:08 UTC on 3 December 2023. The sequence lasted 53 hours and 37 minutes and comprised 49 earthquakes. All events were of low to moderate magnitude, with the largest reaching 2.7. Depths were predominantly shallow, concentrated between 0 and 4 km, although one outlier occurred at 30 km.

The swarm initiated with a 2.7-magnitude event at 1 km depth. Subsequent activity remained largely below magnitude 2.0 for the first several hours, featuring repeated events clustered near 1 km depth. On 2 December, a notable increase in frequency occurred between 09:37 and 12:00 UTC, during which multiple events of magnitude 1.7–2.3 were detected at depths of 1–2 km. The sequence maintained elevated rates through the afternoon before tapering, concluding with a final 1.7-magnitude event at 4 km depth on 3 December.

This swarm aligns with the long-term pattern of seismic activity on Hawaiʻi Island. Since 1 January 2000, 106 swarms have been documented in the region. Annual counts show considerable variability, with notable peaks in 2020 (14 swarms), 2021 (11 swarms), and 2023 (17 swarms). Earlier years recorded fewer events, such as single swarms in 2001, 2005, and 2008.

Hawaiʻi Island’s seismicity is driven by its position over the Hawaiian hotspot, where magma ascent through the Pacific plate generates both volcanic and tectonic earthquakes. The Island of Hawaiʻi hosts five major volcanoes—Kīlauea, Mauna Loa, Hualālai, Mauna Kea, and Kohala—each contributing to distinct seismic regimes. Shallow swarms commonly reflect magma intrusion or pressurization beneath active summit or rift zones, while deeper events may indicate deeper crustal adjustments. Historical monitoring by the U.S. Geological Survey Hawaiian Volcano Observatory confirms that such swarms frequently precede or accompany eruptive episodes, although not all swarms culminate in surface activity.

The VS20231202.1 swarm’s shallow depth distribution and modest magnitudes are consistent with typical intrusive episodes beneath the island’s active volcanic centers. No surface deformation or eruptive phenomena were associated with this particular sequence.

References

• SeismoSight internal swarm classification records for VS20231202.1
• U.S. Geological Survey Hawaiian Volcano Observatory historical seismicity summaries (2000–2023)