Seismic Swarm S20160824.2: Insights into Kilauea’s Activity Near Volcano, Hawaii

An earthquake swarm designated S20160824.2 was recorded 6 km south of Volcano, Hawaii, between 04:43 on 24 August 2016 and 08:20 on 26 August 2016. Over 51 hours and 37 minutes, the sequence produced 38 events, providing a snapshot of shallow crustal dynamics beneath the Island of Hawaiʻi.

The swarm occurred within the tectonically active region influenced by the Hawaiian hotspot. Kilauea volcano, located immediately north of the swarm epicenters, sits above a mantle plume that has built the Hawaiian-Emperor seamount chain over millions of years. The island’s southern flank experiences persistent seaward motion along the basal décollement, generating frequent microseismicity. Depths reported for the 2016 events ranged from the surface to 5 km, with the majority clustered between 0 and 2 km, consistent with brittle failure in the volcanic edifice and shallow rift zones.

Event magnitudes remained modest, peaking at 3.5. The largest shock (3.5 at 2 km depth) occurred at 23:12 on 24 August, accompanied by a 2.5 event at 1 km depth moments earlier. Earlier in the sequence, a 3.3 event was recorded at 22:17. Activity showed two main pulses: an initial cluster on 24 August afternoon and evening, followed by renewed energy around midnight and into the early hours of 25 August. By 26 August, rates declined sharply, with the final recorded event registering magnitude 2.8 at the surface.

Such swarms are common in the Kilauea region. Historical records maintained since 1 January 2000 document 38 comparable swarms, with notable concentrations in 2003 (8 swarms) and 2004, 2007, 2011, and 2012 (4 swarms each). These episodes typically reflect magma intrusion, pressurization of the summit reservoir, or slip along the south flank décollement. The 2016 swarm’s shallow focus and rapid onset–decay pattern align with previously observed intrusive events that did not culminate in eruption.

Monitoring by the U.S. Geological Survey Hawaiian Volcano Observatory continues to track these patterns, integrating seismic, deformation, and gas data to assess hazard. While the 2016 sequence remained non-eruptive, it underscores the persistent seismic vitality of the volcano’s southern sector and the value of dense local networks in distinguishing background swarm activity from precursors to larger events.

References

U.S. Geological Survey, Hawaiian Volcano Observatory – Kilauea seismic monitoring archives
Hawaii Volcano Observatory weekly activity summaries, 2016
Global Volcanism Program, Smithsonian Institution – Kilauea reports