Seismic Insights into Swarm S20190819.1: Hawaii Island Earthquake Activity

Earthquake swarms represent clusters of seismic events occurring in rapid succession without a dominant mainshock, often linked to magmatic or hydrothermal processes in volcanically active regions. Swarm S20190819.1, recorded on the Island of Hawaii, exemplifies this phenomenon within the Hawaiian hotspot setting. The sequence initiated at 15:49 on 18 August 2019 and concluded at 08:42 on 5 September 2019, encompassing 217 earthquakes over 424 hours and 52 minutes.

The Island of Hawaii hosts active shield volcanoes including Kilauea and Mauna Loa, formed by the Pacific plate's movement over a mantle plume. This geology produces frequent seismic swarms driven by magma intrusion, dike propagation, and crustal adjustments. Depths in the provided events predominantly range from 30 to 35 km, consistent with the brittle-ductile transition zone beneath the volcanic edifice, though occasional shallower or deeper occurrences reflect localized stress variations.

Examination of the first 100 events reveals a pattern of low-magnitude activity, with values mostly between 1.7 and 2.2. Initial events on 18 August clustered around 33-35 km depth, transitioning to include a notable 2.6 magnitude at 0 km depth early on 19 August. Subsequent activity maintained steady rates, with brief clusters such as those on 22 August showing multiple events near 34-39 km. A 3.0 magnitude at 3 km depth on 20 August stood as an outlier in both size and shallowness, potentially indicating near-surface fracturing. Overall, the sequence displayed consistent low-energy release without escalation to higher magnitudes.

Hawaii has experienced recurrent swarms since at least 2000, with 27 documented episodes through the present record. Yearly distributions include single events in 2000, 2005, 2006, 2007, 2008, 2011, 2013, and 2014; three each in 2003 and 2004; four in 2015; two in 2016; and seven in 2018. These historical patterns align with ongoing volcanic unrest, where swarms often precede or accompany eruptive phases at Kilauea or Mauna Loa.

This swarm's characteristics reinforce the island's dynamic tectonic environment, where seismic monitoring aids in understanding magma pathways and hazard assessment. Continued observation remains essential for interpreting future sequences in this geologically active locale.

References

USGS Earthquake Catalog Hawaiian Volcano Observatory Reports