Seismic Swarm VS20221128.1 Near Honaunau-Napoopoo, Hawaii: Geological Context and Event Analysis

A significant seismic swarm, classified internally as VS20221128.1, occurred in the region 27 km east of Honaunau-Napoopoo on the Big Island of Hawaii. The swarm initiated at 16:46 on 27 November 2022 and concluded at 18:58 on 8 December 2022, spanning 266 hours and 11 minutes. During this period, 416 earthquakes were recorded, highlighting ongoing tectonic and volcanic processes in one of the world's most active volcanic settings.

The Hawaiian Islands form through hotspot volcanism, where the Pacific Plate moves over a mantle plume, generating the chain of shield volcanoes. On the Big Island, Kilauea and Mauna Loa dominate activity, with frequent magma intrusions and flank movements producing earthquake swarms. The swarm location lies on the southwestern flank, an area influenced by both volcanic unrest and gravitational spreading of the volcanic edifice. Shallow seismicity here often correlates with magma migration or fault adjustments within the volcanic pile.

Historical data since 2000 indicate 25 prior swarms in the region, distributed across years as follows: five in 2004, one each in 2006 and 2012, two in 2015, one in 2016, three in 2017, three in 2020, five in 2021, and four in 2022. These recurrent events underscore the persistent nature of seismic activity tied to Hawaii's dynamic geology.

Analysis of the first 100 events reveals predominantly low-magnitude earthquakes, with values ranging from 1.1 to 4.2. The majority clustered between 1.5 and 3.0, consistent with swarm characteristics rather than mainshock-aftershock sequences. Depths were overwhelmingly shallow, mostly between -4 km and 5 km, reflecting activity within or near the volcanic crust. Negative depth values may indicate events above sea level on the island's slopes. A notable peak occurred on 28 November, including a magnitude 4.2 event at 08:56:25, accompanied by several magnitude 3+ quakes shortly thereafter. Activity showed temporal clustering, with bursts of higher-frequency events interspersed with quieter intervals.

This swarm aligns with patterns observed in Hawaii's volcanic systems, where fluid movement or pressure changes in the subsurface trigger dense earthquake sequences. Such episodes contribute to monitoring efforts by agencies tracking potential precursors to eruptions or significant ground deformation.

References

United States Geological Survey (USGS) Hawaiian Volcano Observatory reports on regional seismicity.
Hawaii Volcanoes National Park geological summaries.
SeismoSight internal swarm classification database.