Seismic Swarm S20241204.1 Near Pāhala, Hawaii: Geological Context and Event Analysis
A notable earthquake swarm, designated S20241204.1 by SeismoSight, occurred 9 km northeast of Pāhala on Hawaii's Big Island. The swarm initiated at 12:13 on 3 December 2024 and concluded at 17:54 on 10 December 2024, spanning 173 hours and 41 minutes. During this period, 138 earthquakes were recorded, with analysis focused on the first 100 events revealing a concentrated sequence of low-to-moderate magnitude activity.
The Pāhala region lies within the seismically active south flank of Kīlauea volcano, part of Hawaii's chain of shield volcanoes formed by hotspot volcanism. This area experiences frequent seismic swarms due to magma movement through the volcanic system, gravitational spreading of the volcano's flanks, and interactions along the décollement fault at the base of the volcanic edifice. Depths in the provided swarm data cluster predominantly between 26 and 37 km, consistent with activity in the deeper crustal levels beneath the Hawaiian volcanic pile, where magma reservoirs and fault zones interact.
Examination of the first 100 events shows magnitudes ranging from 1.0 to 2.9, with the majority falling between 1.5 and 2.5. Depths averaged around 30-33 km for most events, though several shallower occurrences near 7 km and 26-28 km appeared later in the sequence. Timing indicates peak activity on 3-6 December, with multiple events often occurring within minutes of each other, a hallmark of swarm behavior driven by fluid migration or stress transfer rather than a single large rupture. No events exceeded magnitude 3.0 in the initial dataset, underscoring the swarm's non-destructive yet informative nature for monitoring volcanic unrest.
Hawaii has a well-documented history of seismic swarms linked to its active volcanoes. Since 2000, exactly 100 such swarms have been recorded in the region, with notable increases in frequency during periods of heightened volcanic activity. Yearly distribution includes 2 in 2000, 5 in 2003, 5 in 2004, 1 in 2005, 1 in 2006, 2 in 2007, 1 in 2008, 2 in 2011, 3 in 2012, 1 in 2013, 2 in 2014, 4 in 2015, 2 in 2016, 1 in 2017, 7 in 2018, 3 in 2019, 12 in 2020, 10 in 2021, 7 in 2022, 20 in 2023, and 9 in 2024 up to the current event. These patterns correlate with cycles of magma supply and flank instability at Kīlauea and neighboring Mauna Loa.
Such swarms provide critical data for understanding subsurface dynamics in Hawaii's volcanic environment. The consistent depths and clustered timing observed here align with established models of magmatic intrusion and fault slip in the island's south sector. Continued monitoring remains essential given the region's ongoing volcanic history.
References
- SeismoSight internal swarm classification data for S20241204.1 and historical statistics since 2000.
- USGS Hawaiian Volcano Observatory reports on Kīlauea south flank seismicity and volcanic processes.