Seismic Swarm S20231120.1: Analysis of Activity Near Volcano, Hawaii

A seismic swarm designated S20231120.1 occurred 13 km SSW of Volcano, Hawaii, from 00:39 on 20 November 2023 to 00:18 on 22 November 2023. Over 47 hours and 39 minutes, 71 earthquakes were recorded. Magnitudes ranged from 0.1 to 3.0, with the majority below 2.0. Depths were predominantly shallow, between 0 and 6 km, though isolated events reached 11 km and 39 km.

This swarm aligns with patterns typical of Hawaii's volcanic systems. The Island of Hawaii sits above a mantle hotspot that has generated the Hawaiian-Emperor seamount chain over millions of years. The swarm location lies on the south flank of Kīlauea volcano, where frequent microseismicity reflects magma transport, dike intrusion, and gravitational adjustments along rift zones and fault systems.

Kīlauea remains one of Earth's most active volcanoes, with documented eruptions spanning centuries. Its east rift zone and summit caldera produce recurring earthquake swarms linked to magma movement. Historical records from the Hawaiian Volcano Observatory show swarms often precede or accompany eruptive phases, as pressure changes within the shallow magmatic system trigger brittle failure in surrounding rock.

Since 2000, 96 swarms have been identified in the region. Annual counts varied, with notable increases in 2018 (9 swarms), 2020 (13 swarms), and 2023 (14 swarms). These events cluster along the volcano's southern and eastern sectors, consistent with ongoing deformation monitored by GPS and InSAR.

The November 2023 swarm exhibited classic volcanic characteristics: a rapid onset, high event rate over two days, and shallow focal depths. Peak activity occurred on 21 November, including events of magnitude 3.0, 2.8, and 2.7, all at depths of 1 km or less. Such clustering suggests localized stress release possibly driven by fluid migration or minor inflation beneath the surface.

No significant surface deformation or eruptive activity was associated with this specific swarm, distinguishing it from larger pre-eruptive sequences observed in prior years. Continued monitoring remains essential given the area's history of sudden escalations in seismic rates.

References

USGS Hawaiian Volcano Observatory reports on Kīlauea seismicity
SeismoSight internal swarm classification data