Seismic Swarm S20000224.1 Near Volcano, Hawaii: Geological Context and Event Analysis

Seismic swarm S20000224.1 was recorded 7 km south of Volcano, Hawaii, on the Big Island. The sequence began at 05:16 on 23 February 2000 and concluded at 17:11 on 2 March 2000. Over 203 hours and 54 minutes, 216 earthquakes were detected. This activity occurred within the seismically active zone associated with Kilauea volcano, part of the Hawaiian hotspot chain.

The Hawaiian Islands formed through prolonged volcanic activity driven by a mantle plume beneath the Pacific Plate. Kilauea, one of the world's most active volcanoes, lies on the southeastern flank of Mauna Loa and has produced frequent eruptions and associated seismicity for centuries. Shallow earthquake swarms commonly precede or accompany magma movement in the East Rift Zone and summit caldera. Historical records document similar swarms during the 20th century, including episodes linked to the 1983–2018 Puʻuʻōʻō eruption and earlier flank movements.

Analysis of the first 100 events reveals a classic volcanic swarm signature. Magnitudes ranged from 0.5 to 4.0, with the majority below 2.0. Depths were predominantly shallow, concentrated between 0 and 3 km, consistent with brittle failure in the volcanic edifice rather than deeper tectonic sources. A notable 4.0 magnitude event occurred at 00:06:53 on 24 February at 1 km depth, marking the peak energy release early in the sequence. Subsequent events showed rapid clustering, with dozens occurring within minutes during the initial hours.

Temporal patterns indicate an initial intense phase on 23–24 February, followed by a gradual decline. Most events clustered at depths of 1–2 km, suggesting involvement of the shallow hydrothermal or magmatic system. No events exceeded magnitude 3 after the early peak, and activity tapered through late February. These characteristics align with fluid-driven or magma-induced seismicity typical of Kilauea’s rift zones.

The swarm’s location south of Volcano places it near the boundary between the East Rift Zone and the south flank, areas subject to gravitational spreading and occasional slow-slip events. Such activity contributes to the long-term evolution of the island’s southeastern coast.

References
SeismoSight internal classification data for swarm S20000224.1 parameters and event list.
USGS Hawaiian Volcano Observatory summaries on Kilauea seismicity and regional geology.