Seismic Swarm VS20220923.1: Geological Context and Event Analysis on the Island of Hawaii

The Island of Hawaii, the largest and geologically youngest of the Hawaiian archipelago, sits atop the Hawaiian hotspot in the central Pacific Ocean. Formed primarily by five shield volcanoes—Kohala, Mauna Kea, Hualalai, Mauna Loa, and Kilauea—the island experiences persistent seismic activity driven by volcanic processes. Magma movement, crustal deformation, and faulting within the volcanic edifice generate frequent earthquakes, many of which occur in swarms. These swarms represent clusters of events closely spaced in time and location, typically without a single dominant mainshock. Seismic swarms have been documented regularly on the island. Since 2000, 20 swarms have occurred, distributed across years as follows: 2004 (4), 2006 (1), 2015 (2), 2016 (1), 2017 (2), 2020 (2), 2021 (5), and 2022 (3). Such episodes often correlate with unrest at Kilauea or Mauna Loa, where shallow magma intrusions produce low-magnitude events at depths generally less than 5 km. Swarm VS20220923.1 began at 10:17 on 23 September 2022 and concluded at 05:36 on 8 October 2022, spanning 355 hours and 19 minutes. During this interval, 375 earthquakes were recorded. The first 100 events, spanning 23–25 September, exhibited predominantly low magnitudes between 0.4 and 2.7, with the majority below 2.0. Depths clustered near the surface, ranging from -3 km to 10 km, indicating shallow crustal sources consistent with volcanic rather than tectonic origins. Early activity on 23 September featured the highest event rate and included the swarm’s peak magnitude of 2.7, followed by a gradual decline in both frequency and intensity over subsequent days. These characteristics align with typical Hawaiian swarm patterns linked to fluid migration or minor dike propagation beneath the volcanic flanks. No significant surface deformation or eruptive activity was associated with this episode, underscoring its role as a minor unrest signal within the island’s ongoing volcanic system.

References

United States Geological Survey, Hawaiian Volcano Observatory earthquake catalog.
SeismoSight internal swarm classification records.