Seismic Swarm S20180502.1: May 2018 Earthquake Sequence on Hawaii Island

The Island of Hawaii, also known as the Big Island, lies above the Hawaiian hotspot, a mantle plume responsible for the ongoing construction of the Hawaiian-Emperor seamount chain. This intraplate volcanism drives frequent seismic activity as magma migrates through the crust beneath active shield volcanoes such as Kilauea and Mauna Loa. Seismic swarms—clusters of earthquakes occurring in rapid succession without a single dominant mainshock—are common manifestations of these processes, reflecting fluid movement, dike intrusion, and caldera deformation.

Swarm S20180502.1 was recorded on the Island of Hawaii from 21:22 on 1 May 2018 to 06:23 on 10 May 2018. In 201 hours, 196 earthquakes were detected. Analysis of the first 100 events shows predominantly low-magnitude seismicity, with magnitudes ranging from 0.9 to 4.6. Depths were shallow, concentrated between 0 and 13 km, consistent with volcanic rather than tectonic origins. Notable events included a magnitude 3.9 at 22:39 on 4 May, followed shortly by two magnitude 4.6 earthquakes at depths of 7 km and 2 km. These larger events occurred amid a sequence dominated by magnitudes 1.5–2.7, with many events at or near 0 km depth.

This swarm coincided with heightened volcanic unrest at Kilauea, where magma movement preceded the onset of fissure eruptions in the lower East Rift Zone. Shallow seismicity and occasional deeper events up to 26 km illustrate the vertical extent of magmatic pathways beneath the volcano. Negative depth values in the catalog likely represent events near or slightly above sea level within the volcanic edifice.

Historical records indicate that seismic swarms have been recurrent on the Island of Hawaii. Since 1 January 2000, 44 swarms have been identified, with annual counts varying as follows: 2000 (3), 2001 (1), 2003 (7), 2004 (4), 2005 (1), 2006 (2), 2007 (3), 2008 (1), 2011 (2), 2012 (4), 2013 (1), 2014 (2), 2015 (4), 2016 (2), 2017 (2), and 2018 (5). These episodes underscore the persistent influence of hotspot-driven magmatism on regional seismicity.

The May 2018 sequence exemplifies how swarms serve as precursors to eruptive activity, providing critical data for monitoring magma ascent and assessing volcanic hazards in one of Earth’s most active volcanic regions.

References

USGS Hawaiian Volcano Observatory reports on Kilauea activity (2018)
Hawaii Seismic Network earthquake catalog summaries
Geological Society of America publications on Hawaiian hotspot volcanism