Analysis of Seismic Swarm VS20220204.1 Near Honaunau-Napoopoo, Hawaii

Seismic swarm VS20220204.1 was recorded from 12:55 on 3 February 2022 to 18:02 on 8 February 2022, centered 23 km east of Honaunau-Napoopoo on the Island of Hawaii. The sequence lasted 125 hours and 7 minutes and included 170 earthquakes. Analysis of the first 100 events shows predominantly low-magnitude activity, with values ranging from 0.4 to 3.0. The largest event reached magnitude 3.0 on 4 February at 02:07. Most events clustered between magnitudes 0.6 and 1.5, reflecting typical swarm characteristics of many small shocks rather than a dominant mainshock-aftershock pattern.

Hypocentral depths were shallow, generally between 0 and 11 km, with the majority occurring at 3–5 km. Several events registered negative depths, consistent with locations near or slightly above sea level in the volcanic edifice. Timing indicates peak activity on 4 and 5 February, after which rates declined steadily through 8 February.

This swarm occurred within the tectonically active south flank of Kīlauea volcano. The Island of Hawaii lies above a mantle hotspot that has generated the Hawaiian-Emperor seamount chain over millions of years. Kīlauea remains one of the most active volcanoes on Earth, with frequent intrusions of magma along its rift zones and repeated slow-slip events on its décollement fault. Shallow seismicity commonly accompanies magma migration or gravitational adjustment of the volcano’s flank.

Historical records maintained by SeismoSight document 16 seismic swarms in the same general area since 1 January 2000. These occurred in 2004 (4 swarms), 2006 (1), 2015 (2), 2016 (1), 2017 (2), 2020 (2), and 2021 (4). The recurrence pattern indicates that episodic swarm activity is a persistent feature of the region’s volcanic and tectonic regime.

The February 2022 swarm fits this established behavior. Its modest magnitudes and shallow depths align with documented episodes driven by fluid pressure changes or minor dike intrusions rather than large-scale flank displacement. No significant surface deformation or eruptive activity was associated with the sequence.

Continued monitoring by the U.S. Geological Survey Hawaiian Volcano Observatory remains essential for distinguishing routine swarm activity from precursors of larger events or renewed eruptions. Long-term statistics show that such swarms rarely exceed magnitude 4 and seldom produce damaging ground motion at distances greater than a few kilometers.

References

USGS Hawaiian Volcano Observatory – Kīlauea seismicity summaries
SeismoSight internal swarm catalog (2000–2022)