Seismic Insights into Swarm S20070524.1: Kilauea’s Dynamic Crust

The region 7 km south of Volcano, Hawaii, lies on the southern flank of Kilauea, one of Earth’s most active shield volcanoes. Situated above the Hawaiian hotspot, this area experiences persistent volcanic and tectonic activity driven by magma ascent and flank movement along the Hilina fault system. Kilauea’s summit caldera and east rift zone have produced frequent eruptions and associated seismicity for centuries, with documented activity extending back through Hawaiian oral histories and into modern instrumental records beginning in the early 20th century. Swarm S20070524.1 began at 03:21 on 24 May 2007 and concluded at 14:53 on 3 June 2007. Over 251 hours and 32 minutes, 114 earthquakes were recorded. The sequence clustered at shallow depths, predominantly between 0 and 3 km, with occasional events reaching 10 km. Magnitudes ranged from 0.9 to 4.7, highlighting the swarm’s low-to-moderate energy release typical of volcanic-tectonic unrest rather than a single large rupture. Analysis of the first 100 events reveals a clear temporal pattern. The initial 24 hours featured the strongest activity, including a 4.7 magnitude event at 19:13 on 24 May and a 4.1 event shortly afterward, both at depths of 0–2 km. Subsequent hours showed rapid aftershock decay interspersed with renewed bursts, such as the 3.9 magnitude shock at 20:51. By 25–26 May, magnitudes had decreased, with most events below 2.5 and depths remaining shallow. Later phases from 27 May onward exhibited slightly deeper foci (5–10 km) and lower magnitudes, suggesting migration or adjustment of stress within the volcanic edifice. This swarm fits within a broader historical context. Since 1 January 2000, twenty earthquake swarms have occurred in the immediate region. Yearly tallies include three in 2000, one in 2001, eight in 2003, five in 2004, one in 2005, and two in 2006. Such recurrence underscores Kilauea’s ongoing magmatic and structural adjustments, often preceding or accompanying eruptive episodes. Geologically, these swarms arise from the interplay between magma intrusion along rift zones and gravitational instability of the volcano’s south flank. The 2007 sequence likely reflects fluid pressure changes and minor slip on pre-existing faults, consistent with Kilauea’s long-term behavior. No surface rupture or major eruptive event was directly linked, illustrating how many Hawaiian swarms dissipate without culminating in visible volcanism. Continued monitoring by the Hawaiian Volcano Observatory remains essential for distinguishing benign swarms from precursors to larger unrest. The detailed temporal and magnitude distribution of S20070524.1 provides valuable data for refining models of volcanic seismicity in basaltic shield environments. References
USGS Earthquake Catalog (historical swarm statistics)
Hawaiian Volcano Observatory reports on Kilauea activity (2000–2007)
SeismoSight internal swarm classification database