Seismic Swarm S20200511.2 in the Hawaii Region

A notable earthquake swarm designated S20200511.2 occurred in the Hawaii region from 13:35 on 11 May 2020 to 05:41 on 15 May 2020. Over 88 hours and 5 minutes, the swarm produced 131 earthquakes. Analysis of the first 100 events reveals a rapid onset with events clustered in the initial hours, followed by sustained activity through the first day. Magnitudes ranged primarily between 1.4 and 3.9, with the largest events reaching 3.9 on 11 May at 21:59 and again on 12 May at 02:04. Depths concentrated between 5 and 12 km, consistent with shallow crustal processes.

The temporal distribution shows intense sequences on 11 May evening and into 12 May morning, including multiple pairs of nearly simultaneous events at similar depths. Later events maintained similar magnitude and depth patterns, indicating ongoing stress release without significant migration. This pattern aligns with fluid-driven or magmatic intrusion mechanisms typical in volcanic settings.

Hawaii lies above a mantle hotspot that has generated the Hawaiian-Emperor seamount chain over tens of millions of years. The islands consist of massive shield volcanoes built by successive basaltic lava flows. Seismic activity here arises mainly from volcanic processes such as magma movement, dike propagation, and gravitational adjustments of the volcanic edifice rather than plate-boundary tectonics. Depths of 5–12 km correspond to the brittle-ductile transition zone beneath the volcanoes where magma reservoirs commonly reside.

Since 2000, only three prior swarms have been recorded in the region: one each in 2001, 2005, and 2017. The 2020 swarm therefore represents a relatively infrequent episode. Such swarms can precede or accompany eruptive phases at Kilauea or Mauna Loa, although many remain aseismic at the surface.

The 2020 sequence underscores the persistent volcanic hazard in Hawaii. Continuous monitoring by the Hawaiian Volcano Observatory remains essential for distinguishing benign swarms from those that may escalate to eruption.

References

USGS Earthquake Catalog Hawaiian Volcano Observatory reports