Seismic Swarm S20120529.2: Analysis of Activity Near Volcano, Hawaii

Seismic swarm S20120529.2 occurred 15 km south-southeast of Volcano, Hawaii, registering 67 earthquakes between 20:47 on 28 May 2012 and 05:17 on 3 June 2012. The sequence lasted 128 hours and 30 minutes, with events clustered at shallow depths consistent with volcanic and tectonic processes in the region.

The Hawaiian Islands form through hotspot volcanism, where the Pacific Plate moves over a mantle plume, producing the active volcanoes of Kilauea and Mauna Loa on the Big Island. This tectonic setting generates frequent earthquake swarms driven by magma movement, flank instability, and faulting along rift zones. Depths in the swarm ranged from surface level to 11 km, typical for upper-crustal activity associated with these volcanoes.

Event magnitudes remained predominantly below 2.5, indicating low-energy release distributed across many small quakes rather than a single mainshock. The largest recorded event reached magnitude 3.2 at 10 km depth on 30 May at 06:21, followed closely by a magnitude 3.0 at the same depth later that day. Shallower events, often 1–5 km deep, clustered during the first 48 hours, while deeper activity appeared toward the swarm’s conclusion on 3 June.

Temporal patterns show peak frequency on 29 and 30 May, with multiple magnitude 2+ events spaced hours apart. Later stages featured lower-magnitude, more sporadic quakes, suggesting gradual release of accumulated stress. Depths generally increased slightly over time, possibly reflecting migration of fluids or magma along subsurface pathways.

Since 1 January 2000, 29 swarms have been documented in the area. Yearly distribution includes three in 2000, one in 2001, eight in 2003, five in 2004, one each in 2005 and 2006, four in 2007, one in 2008, three in 2011, and one in 2012 prior to this sequence. Such recurrence underscores the persistent volcanic and structural dynamics southeast of Volcano.

This swarm aligns with historical patterns of distributed seismicity in Hawaii’s volcanic flanks, where magma-induced stresses produce swarms without leading to immediate eruptions. Monitoring of similar sequences aids in distinguishing background volcanic tremor from potential precursors.

References

USGS Hawaiian Volcano Observatory reports on Kilauea seismicity and regional tectonics.