Seismic Swarm S20150423.1: Analysis of Activity Southwest of Volcano, Hawaii

An earthquake swarm designated S20150423.1 occurred 5 km southwest of Volcano, Hawaii, on the Big Island. The sequence began at 20:28 HST on 22 April 2015 and concluded at 22:41 HST on 17 May 2015. Over 602 hours and 13 minutes, 2,099 earthquakes were recorded. This event aligns with patterns of seismic unrest common to the Kilauea volcanic system.

The region lies within the Hawaii hotspot province, where the Pacific plate moves over a mantle plume, fueling ongoing shield volcanism. Kilauea, one of five volcanoes comprising the island, has exhibited persistent activity for centuries. Its east rift zone and summit caldera frequently host earthquake swarms linked to magma migration through dikes and sills. Depths in this swarm ranged primarily from surface levels to about 10 km, consistent with shallow crustal processes above the volcano's magma reservoir.

Analysis of the first 100 events reveals a rapid onset with events clustered in the initial 48 hours. Magnitudes stayed modest, spanning 0.1 to 2.4, while depths concentrated between 0 and 4 km, with occasional deeper outliers. Timing showed bursts of activity separated by quieter intervals, typical of fluid-driven seismicity rather than tectonic mainshock-aftershock sequences. Such patterns reflect incremental stress changes from ascending magma or hydrothermal fluids.

Hawaii has recorded 36 swarms since 2000, underscoring the repetitive nature of volcanic seismicity. Yearly counts include three in 2000, one in 2001, eight in 2003, five in 2004, one in 2005, two in 2006, four in 2007, one in 2008, three in 2011, four in 2012, one in 2013, two in 2014, and one in 2015. These episodes often precede or accompany eruptive phases, providing critical monitoring data for hazard assessment.

This swarm contributed to broader understanding of Kilauea's dynamic plumbing system. Continuous seismic monitoring by the Hawaiian Volcano Observatory supports real-time evaluation of unrest, aiding public safety in this geologically active setting.

References

USGS Hawaiian Volcano Observatory reports on Kilauea seismicity (2015 updates).
Hawaii Volcanoes National Park geological summaries.
Peer-reviewed studies on Hawaiian hotspot volcanism in Journal of Volcanology and Geothermal Research.