Seismic Swarm Activity in the Maug Islands Region

A seismic swarm designated PS20231124.1 occurred in the Maug Islands region of the Northern Mariana Islands. The sequence began at 09:05 UTC on 24 November 2023 and ended at 17:18 UTC on 25 November 2023, lasting 32 hours and 13 minutes. Sixteen earthquakes were recorded during this interval.

The swarm initiated with a magnitude 6.9 event at 22 km depth. Subsequent activity consisted primarily of events between magnitude 4.8 and 5.6, with most occurring at approximately 10 km depth. Additional notable shocks included magnitude 5.4, 5.2, and multiple 5.1 events on 24 November, followed by two magnitude 5.6 earthquakes on 25 November that marked the conclusion of the swarm.

Since 1 January 2000, only two prior swarms have been documented in the region, occurring in 2016 and 2021. These episodes reflect episodic clustering rather than continuous high-frequency seismicity.

The Maug Islands form part of the Mariana volcanic arc, generated by subduction of the Pacific Plate beneath the Philippine Sea Plate. Convergence rates in this segment exceed 40 mm per year, producing a steeply dipping Wadati-Benioff zone that extends to depths greater than 600 km. The islands themselves represent the emergent portions of submerged volcanic calderas aligned along the arc front. This tectonic framework accounts for the region’s persistent volcanic and seismic hazards, including frequent moderate-to-large thrust and normal-faulting earthquakes.

References: SeismoSight internal swarm classification PS20231124.1 USGS Earthquake Hazards Program – Mariana Islands tectonics summary Smithsonian Institution Global Volcanism Program – Maug Islands entry