Earthquake Swarm S20161125.1: Geological Context and Event Analysis on Hawaiʻi Island

Earthquake swarms represent clusters of seismic events occurring in rapid succession without a dominant mainshock, often linked to volcanic or magmatic processes. Swarm S20161125.1, recorded on the Island of Hawaiʻi, began at 04:52 on 24 November 2016 and concluded at 17:08 on 28 November 2016. Over 108 hours and 16 minutes, 47 earthquakes were detected, with magnitudes ranging from 0.4 to 3.0 and depths predominantly between 0 and 5 km, except for two events near 28–29 km.

The sequence initiated with paired events at 04:52 on 24 November, registering magnitudes of 0.7 and 2.0. Subsequent activity showed repeated clustering, particularly on 24 November, with multiple pairs exceeding magnitude 2.0 at shallow depths under 3 km. Notable peaks included a magnitude 3.0 event at 23:16 on 24 November and a magnitude 2.8 at 17:24 on 25 November. Activity tapered after 26 November, with isolated deeper events on 28 November at approximately 28–29 km depth reaching magnitudes 2.9 and 2.3. These patterns indicate episodic shallow fracturing consistent with fluid migration or stress adjustments in volcanic terranes.

Hawaiʻi Island lies above the Hawaiian hotspot, where the Pacific Plate moves northwest over a mantle plume, fueling the growth of shield volcanoes including Kīlauea, Mauna Loa, and Mauna Kea. This tectonic setting produces frequent shallow seismicity through magma intrusion, dike propagation, and gravitational flank instability. Historical records document 39 swarms since 2000, with elevated frequencies in 2003 (8 swarms) and 2004 (5 swarms). Such recurrent swarms reflect ongoing volcanic-tectonic interactions that have shaped the island’s geology over millennia.

The 2016 swarm aligns with typical pre-eruptive or intrusive signatures observed at Kīlauea’s East Rift Zone and summit regions, where low-magnitude events dominate due to brittle failure in basalt. Depths under 5 km correspond to the volcanic edifice, while the deeper pair may relate to deeper conduit adjustments. No surface deformation or eruptive activity was directly tied to this specific sequence in available records.

Long-term monitoring by the Hawaiian Volcano Observatory underscores that swarms contribute to hazard assessment by signaling potential magma movement. Continued seismic surveillance remains essential given the island’s dynamic volcanic environment.

References

United States Geological Survey, Hawaiian Volcano Observatory reports on regional seismicity.
Hawaiian Volcano Observatory, historical earthquake swarm catalog (2000–2016).