Seismic Swarm VS20200904.1: Analysis of Activity Near Volcano, Hawaii

Seismic swarm VS20200904.1 was recorded 5 km SSW of Volcano, Hawaii, beginning at 19:23 on 3 September 2020 and concluding at 01:29 on 5 September 2020. Over this 30-hour period, 64 earthquakes were detected, providing a detailed snapshot of localized crustal dynamics in one of Earth's most active volcanic regions.

The events clustered at shallow depths, predominantly between 0 and 6 km, with isolated occurrences reaching 11 km. Magnitudes remained low, ranging from 0.3 to 2.4, consistent with typical microseismicity patterns. The initial event registered 2.4 at 6 km depth, followed by a rapid succession of smaller tremors. A notable cluster occurred around 13:13 on 4 September, including a 2.2 magnitude shock at 2 km and concurrent events at similar depths. Later activity tapered with isolated readings up to 1.7 magnitude near the swarm's end.

This swarm fits within established patterns of seismicity on the Island of Hawaii. The location lies on the south flank of Kilauea volcano, part of the Hawaiian hotspot chain formed by a mantle plume beneath the Pacific plate. Kilauea has exhibited persistent volcanic and seismic behavior for centuries, driven by magma ascent, flank instability, and interaction with the underlying oceanic crust. Earthquake swarms here often reflect fluid migration, stress accumulation along rift zones, or adjustments in the volcanic edifice rather than large tectonic releases.

Historical records indicate 62 such swarms in the region since 1 January 2000. Yearly distribution shows variability, with peaks in 2003 (8 swarms), 2018 (9 swarms), and 2020 (6 swarms up to the date of this event). Earlier years such as 2000, 2004, and 2015 each recorded between 3 and 6 swarms, underscoring recurrent episodic unrest tied to Kilauea's eruptive cycles.

Geological context highlights the area's position within the East Rift Zone and adjacent Hilina fault system. These structures accommodate extension and slumping of the volcanic flank, generating frequent low-magnitude sequences. Depths in the provided data align with shallow brittle failure above the ductile transition zone influenced by heat from the hotspot. Such activity contributes to monitoring efforts that track potential precursors to larger eruptions or flank movements.

Insights from the swarm reveal a typical progression: an energetic onset, sustained low-level repetition over daytime hours on 4 September, and gradual decay. Most events at 0–1 km depth suggest near-surface processes, while deeper outliers may indicate connections to magma reservoirs. This distribution supports models of distributed fracturing rather than a single fault rupture.

Continued observation of these patterns aids in refining hazard assessments for nearby communities. The 2020 swarm exemplifies the persistent, low-intensity seismicity that characterizes Hawaii's dynamic landscape.

References

USGS Hawaiian Volcano Observatory reports on Kilauea seismicity.
Hawaii Volcanoes National Park geological summaries.
Peer-reviewed studies on Hawaiian hotspot volcanism in Journal of Volcanology and Geothermal Research.