Seismic Swarm VS20210805.1: Analysis of Activity Near Volcano, Hawaii

A seismic swarm designated VS20210805.1 occurred 5 km SSW of Volcano, Hawaii, from 16:28 on 4 August 2021 to 10:32 on 13 August 2021. Over 210 hours and 4 minutes, 279 earthquakes were recorded. This event aligns with the region's established pattern of swarm activity driven by volcanic processes at Kīlauea.

Kīlauea, on the Big Island of Hawaii, ranks among the world's most active volcanoes. Its geology features a summit caldera and rift zones where magma movement frequently triggers shallow seismicity. The swarm location lies within the volcano's southern flank, an area of ongoing deformation and faulting associated with the East Rift Zone.

Analysis of the first 100 events reveals predominantly low-magnitude earthquakes. Magnitudes ranged from 0.2 to 2.5, with the majority below 2.0. Depths clustered between 0 and 2 km, indicating shallow crustal sources typical of volcanic swarms, though isolated events reached 5 km and one outlier at 31 km. Temporal distribution showed peak activity on 5 August, with multiple events exceeding magnitude 2.0 occurring within hours. Later events maintained similar characteristics, underscoring sustained but non-escalating energy release.

Such swarms reflect fluid migration or stress adjustments in the volcanic system rather than tectonic mainshock-aftershock sequences. Hawaii's historical record confirms frequent recurrence, with 72 swarms documented since 2000. Annual counts varied, including peaks in 2018 (9 swarms) and 2020 (13 swarms), consistent with eruptive cycles at Kīlauea.

The 2021 swarm fits this context without indicating unusual escalation. Depths and magnitudes align with prior monitoring data from the region, where shallow events predominate due to the thin oceanic crust and active magma plumbing.

References

United States Geological Survey, Hawaiian Volcano Observatory reports on Kīlauea seismicity (ongoing monitoring data).
Hawaii Volcanoes National Park geological summaries.
SeismoSight internal swarm classification records.