Seismic Swarm PS20241107.1 in the Volcano Islands Region
The Volcano Islands form part of Japan's Ogasawara archipelago in the western Pacific, situated along the Izu-Bonin-Mariana subduction zone. This tectonic setting arises from the Pacific Plate subducting beneath the Philippine Sea Plate, generating frequent seismic activity and volcanic features across the arc. The region experiences moderate to strong earthquakes due to ongoing plate convergence at rates of approximately 4–6 cm per year, with hypocenters often concentrated at shallow to intermediate depths.
SeismoSight recorded swarm PS20241107.1 beginning at 22:55 on 6 November 2024 and concluding at 19:53 on 7 November 2024. Over 20 hours and 58 minutes, seven earthquakes occurred in the Volcano Islands area. The sequence initiated with a magnitude 5.8 event at 8 km depth, followed shortly by two magnitude 5.1 shocks at 10 km. Subsequent events included a magnitude 5.2 at 01:11 on 7 November, a magnitude 4.2 at 01:36, a magnitude 5.0 at 02:12, and a final magnitude 5.1 at 19:53, all at 10 km depth except the initial shock.
This swarm reflects clustered seismicity typical of subduction-related stress release, where multiple events occur in rapid succession without a single dominant mainshock-aftershock pattern. Depths clustered near 10 km suggest activity within the upper crust or near the plate interface. No larger events or significant aftershock migration beyond the listed sequence were noted in the internal classification.
Historical records since 2000 indicate only three prior swarms in the same region, occurring in 2010 with two events and in 2011 with one event. These infrequent clusters underscore that while background seismicity persists, intense swarms remain uncommon, potentially linked to episodic fluid migration or localized stress accumulation along the arc.
The November 2024 swarm adds to understanding of the Volcano Islands' dynamic geology, where volcanic islands such as Iwo Jima overlie active magmatic systems influenced by the same subduction processes. Continued monitoring supports assessment of potential escalation, though current data show contained energy release within moderate magnitudes.
References
- SeismoSight internal swarm classification records
- USGS Earthquake Catalog for regional tectonics
- Japan Meteorological Agency seismic summaries for Izu-Bonin arc history