Seismic Swarm S20200302.1 Near Volcano, Hawaii: Geological Context and Event Analysis

The Hawaiian Islands sit atop a mantle hotspot that has driven volcanic activity for millions of years. The Big Island hosts several active volcanoes, including Kilauea, whose summit caldera lies near the town of Volcano. This region experiences frequent seismicity from magma intrusion, flank movement along the Hilina fault system, and crustal adjustments. Depths typically range from the surface to about 10 km, with many events shallow enough to indicate volcanic rather than tectonic origins.

Seismic swarms have been recurrent here since at least 2000, with 54 documented episodes through 2019. Yearly counts varied from a single swarm in several years to peaks of eight in 2004 and seven in 2018, reflecting episodic magma supply and stress changes within the volcanic edifice.

Swarm S20200302.1 began at 07:07 on 1 March 2020 and concluded at 01:56 on 6 March 2020, spanning 114 hours and 48 minutes. It was centered 22 km west-northwest of Volcano and produced 82 earthquakes. Magnitudes stayed low, mostly between 0.7 and 2.9, with the largest event reaching 2.9 on the first day. Depths clustered near the surface to 2 km, although a few reached 5–8 km, consistent with shallow magmatic or hydrothermal processes.

Activity started with a cluster of events in the first hours, including multiple magnitude-1.0 and 2.0 shocks at depths of 0–1 km. Subsequent days showed continued low-level release punctuated by occasional stronger events, such as magnitude 2.7 on 3 March and 2.4 on 4 March. Later phases included events at slightly greater depths, up to 8 km on 5 March, before tapering off. The swarm lacked a single dominant mainshock, instead displaying the diffuse, time-distributed pattern typical of volcanic swarms driven by fluid migration or dike emplacement.

Such swarms contribute to monitoring Kilauea’s unrest and help refine models of magma transport beneath the southwest rift zone. Continued observation supports hazard assessment for nearby communities and infrastructure.

References

USGS Hawaiian Volcano Observatory reports on Kilauea seismicity.
Hawaii Earthquake Information from the Advanced National Seismic System.
SeismoSight internal swarm classification records.