Seismic Swarm S20201021.1: Analysis of Earthquake Activity on the Island of Hawaii
Seismic swarm S20201021.1 occurred on the Island of Hawaii from 02:54 on 20 October 2020 to 15:18 on 22 October 2020. Over this 60-hour period, 37 earthquakes were recorded, with magnitudes ranging from 1.6 to 2.7. Depths predominantly clustered between 29 and 49 km, though isolated events reached shallower levels near 0–3 km.
The sequence began with a rapid series of events on 20 October, including two magnitude 2.7 quakes at depths of 48 km and 49 km. Activity continued intermittently through 21 October, featuring a notable shallow event of magnitude 2.5 at 3 km depth. The swarm concluded with a final magnitude 1.8 event on 22 October at 29 km depth. Such clustering of similar-magnitude events over a short timeframe is characteristic of volcanic regions where fluid migration or stress adjustments occur.
The Island of Hawaii hosts active shield volcanoes, primarily Kīlauea and Mauna Loa, whose magmatic systems drive much of the regional seismicity. Earthquake swarms here often reflect magma movement through the crust or adjustments along volcanic flanks rather than purely tectonic processes. Depths in the 30–50 km range align with the lower crust and upper mantle transition beneath the island, where magma reservoirs can influence fracture propagation.
Historical records indicate 51 swarms on the Island of Hawaii since 1 January 2000. Annual counts show variability, with peaks in 2018 (8 swarms) and elevated activity in 2003 (6), 2015 (4), and 2020 (6). This pattern underscores recurring unrest linked to the island’s ongoing volcanic construction and flank instability.
This swarm provides insight into potential subsurface dynamics, including possible magma intrusion or hydrothermal fluid movement. Continued monitoring remains essential given the proximity to populated areas and infrastructure on the Big Island.
References
- United States Geological Survey Earthquake Catalog
- Hawaii Volcano Observatory seismic reports
- SeismoSight internal swarm classification data