Seismic Swarm VS20010521.1 Near Volcano, Hawaii: Geological Context and Event Analysis

The seismic swarm designated VS20010521.1 occurred 5 km west-southwest of Volcano, Hawaii, on the Big Island. This event, recorded by the SeismoSight network, began at 14:59 on 20 May 2001 and concluded at 02:15 on 22 May 2001. Over 35 hours and 16 minutes, the swarm produced 28 earthquakes, providing insight into localized crustal stress within one of Earth’s most active volcanic regions.

Hawaii’s geology stems from the Hawaiian hotspot, a mantle plume that has generated the Hawaiian-Emperor seamount chain over tens of millions of years. The Big Island represents the youngest expression of this volcanism, with Kīlauea and Mauna Loa as primary centers. The swarm’s location places it near Kīlauea’s southwest flank, where magma intrusion and flank movement frequently trigger shallow seismicity. Depths in the recorded events ranged from surface levels to 46 km, consistent with both volcanic and tectonic processes in the region.

The sequence opened with a magnitude 1.5 event at 3 km depth on 20 May. Subsequent activity included multiple events between 1.3 and 1.7 magnitude clustered between 3 km and 13 km depth during the evening hours. On 21 May, a pair of magnitude 1.9 earthquakes occurred at 1 km depth, followed by the swarm’s largest event—a magnitude 2.3 quake at 2 km. Later activity shifted to slightly greater depths, culminating in a magnitude 1.5 event at 46 km on 22 May. These patterns reflect typical swarm behavior driven by fluid migration or stress adjustment rather than a single mainshock-aftershock sequence.

Since 1 January 2000, three such swarms have been documented in the area, with the earliest occurring in 2000. This frequency aligns with Kīlauea’s long-term eruptive and intrusive cycles, which have shaped the island’s landscape through repeated lava flows and rift-zone deformation.

The 2001 swarm underscores the persistent seismic hazard associated with Hawaii’s active volcanoes. Continued monitoring remains essential for understanding magma movement and mitigating risks to nearby communities and infrastructure.