Seismic Swarm S20231208.1 Near Volcano, Hawaii

Seismic swarm S20231208.1 was recorded 6 km south of Volcano, Hawaii, on the Big Island. The sequence began at 01:26 on 7 December 2023 and concluded at 15:16 on 9 December 2023, spanning 61 hours and 50 minutes. During this interval, 59 earthquakes were detected, with magnitudes ranging from 0.4 to 4.3 and focal depths primarily between 0 and 3 km, although one event reached 23 km. The swarm exhibited a typical pattern of clustered, low-to-moderate magnitude events concentrated in the shallow crust. A notable outlier was the magnitude 4.3 earthquake at 03:16 on 7 December, occurring at 23 km depth, while the majority of activity remained above 3 km. Multiple events clustered around magnitudes 1.7–2.7 during the peak periods on 7 and 8 December, consistent with fluid migration or stress adjustments in the volcanic edifice. This region lies on the south flank of Kīlauea volcano within the Hawaii Volcanoes National Park area. Kīlauea is one of the world’s most active shield volcanoes, built by successive basaltic lava flows from a summit caldera and rift zones. The volcano sits above the Hawaiian hotspot, where magma ascends through the Pacific plate, producing frequent intrusions, eruptions, and associated seismicity. Historical monitoring by the U.S. Geological Survey Hawaiian Volcano Observatory has documented persistent background earthquakes and episodic swarms linked to magma movement along the East Rift Zone and south flank décollement. Since 2000, 106 seismic swarms have been identified in the immediate vicinity. Annual counts show marked variability: three in 2000, one in 2001, seven each in 2003 and 2004, one in 2005, two in 2006, three in 2007, one in 2008, three in 2011, four in 2012, one in 2013, two in 2014, five in 2015, two each in 2016 and 2017, eight in 2018, four in 2019, fourteen in 2020, ten in 2021, seven in 2022, and nineteen in 2023. Elevated swarm frequency in recent years aligns with renewed eruptive episodes at Kīlauea, including the 2018 lower East Rift Zone eruption and subsequent summit activity. Such swarms commonly precede or accompany magma intrusion or flank slip, though most remain non-eruptive. Depths under 3 km indicate involvement of the shallow volcanic system, while deeper events may reflect adjustments along the volcanic basement. Continued monitoring is essential given the area’s history of rapid changes in activity. References
U.S. Geological Survey Hawaiian Volcano Observatory – Kīlauea monitoring reports and seismic catalogs (ongoing).
Hawaii Volcanoes National Park geological summaries (National Park Service).
SeismoSight internal swarm classification database.