Seismic Swarm S20180505.1: Geological Context and Event Analysis in Hawaii

Seismic swarm S20180505.1 was recorded southeast of Fern Forest on Hawaii's Big Island, beginning at 16:17 on 4 May 2018 and concluding at 15:34 on 23 May 2018. The sequence lasted 455 hours and 17 minutes, encompassing 726 earthquakes. This activity occurred in a region shaped by the Hawaiian hotspot, where the Pacific plate moves over a mantle plume, fueling the growth of shield volcanoes including Kilauea and Mauna Loa.

The Big Island's geology features frequent low-magnitude seismicity driven by magma intrusion, flank movement, and volcanic unrest. Depths in the swarm data predominantly ranged from 0 to 9 km, consistent with shallow crustal processes near active rift zones. A notable event of magnitude 5.7 occurred at 21:32 on 4 May at 6 km depth, followed by a magnitude 4.3 shock minutes later. Subsequent events remained mostly below magnitude 3.5, illustrating the swarm's characteristic pattern of clustered, moderate-energy releases rather than isolated large quakes.

Analysis of the first 100 events reveals a rapid onset with varied magnitudes and shallow focal depths. Initial shocks included magnitudes of 2.5, 0.8, and 1.0 within the first hours, escalating to the 5.7 peak. Depths stayed largely under 10 km, with occasional deeper readings up to 13 km. Magnitudes clustered between 1.0 and 3.4 after the initial spike, reflecting sustained but diminishing energy release typical of magma-driven swarms. This distribution aligns with volcanic settings where fluid migration triggers numerous small fractures.

Hawaii has experienced recurrent swarms since 2000, totaling 46 documented episodes. Yearly counts show peaks in 2003 (8 swarms) and elevated activity in 2018 (5 swarms), underscoring the island's persistent seismic-volcanic regime. Such sequences often precede or accompany eruptive phases, as magma movement stresses surrounding rock.

The 2018 swarm fits within this historical framework, highlighting ongoing monitoring needs in this dynamic hotspot environment. Reliable sources for regional geology include the U.S. Geological Survey volcano observatories and peer-reviewed studies on Hawaiian tectonics.

References

U.S. Geological Survey, Hawaiian Volcano Observatory reports on Kilauea activity.
Hawaii Seismic Network data archives.
Geological Society of America publications on hotspot volcanism.