Earthquake Swarm VS20201202.1: Seismic Activity Near Kīlauea Volcano, Hawaii
Earthquake swarm VS20201202.1 was recorded 7 km southwest of Volcano, Hawaii, on the Big Island. The sequence began at 22:07 on 1 December 2020 and concluded at 00:42 on 25 December 2020, spanning 554 hours and 35 minutes. A total of 641 earthquakes were detected during this period.
This swarm occurred within the seismically active zone associated with Kīlauea, one of the world's most active shield volcanoes. Kīlauea forms part of the Hawaiian hotspot chain, where magma rises through the Pacific Plate, producing frequent shallow seismic events linked to magma movement, dike intrusions, and rift-zone deformation. Depths in the provided events cluster between 0 and 3 km, consistent with typical upper-crustal activity beneath the volcano's south flank and Southwest Rift Zone.
Analysis of the first 100 events reveals predominantly low-magnitude earthquakes. Magnitudes ranged from 0.3 to 2.5, with the majority below 1.0. The two largest events reached 2.5 on 2 December at 10:06 and 2.4 at the swarm's onset. Depths remained shallow, mostly 0–2 km, with only a few events at 3 km. Timing shows an initial burst of activity on 1–2 December, followed by sustained low-level seismicity through early 3 December. Such patterns align with episodic magma pressurization rather than tectonic fault slip.
Hawaii has experienced recurrent earthquake swarms since systematic monitoring began. Since 1 January 2000, 66 swarms have been documented in the region. Annual counts include three in 2000, eight in 2003, nine in 2018, and eleven in 2020, underscoring the persistent volcanic influence on local seismicity. These swarms often precede or accompany eruptive phases at Kīlauea, reflecting the dynamic interplay between the summit caldera, rift zones, and mobile south flank.
The 2020 swarm fits within this established framework. Its shallow focus and high event rate without a dominant mainshock are characteristic of volcanic rather than tectonic sequences. Continued monitoring by the U.S. Geological Survey Hawaiian Volcano Observatory remains essential for interpreting any escalation toward surface deformation or eruptive activity.
References
- SeismoSight internal swarm classification VS20201202.1
- U.S. Geological Survey Hawaiian Volcano Observatory volcanic and seismic monitoring data
- Geological context from USGS Professional Papers on Kīlauea volcano structure and history