Seismic Activity and Geology of the Pagan Region, Northern Mariana Islands

The Pagan region lies within the Northern Mariana Islands, an arc of volcanic islands situated above the Mariana subduction zone. Here the Pacific Plate descends beneath the Philippine Sea Plate, producing one of Earth’s most seismically active environments. The subduction interface reaches depths exceeding 200 km beneath the islands, generating both shallow crustal events and intermediate-depth earthquakes within the descending slab.

On 31 October 2007 at 03:30 UTC, a magnitude 7.2 earthquake struck directly beneath Pagan at a focal depth of 207 km. The event originated within the subducting Pacific slab, consistent with the region’s characteristic Wadati-Benioff zone seismicity. Two additional magnitude 7.7 earthquakes occurred nearby on 29 July 2016, located 37 km and 41 km from the 2007 hypocenter, respectively. All three events illustrate the persistent release of strain along the steeply dipping slab.

Geologically, the Northern Mariana Islands occupy the fore-arc and volcanic front of the subduction system. Pagan itself is a composite stratovolcano whose edifice rises more than 2 km above the seafloor. Magma generation is driven by dehydration of the subducting plate, which lowers the melting point of the overlying mantle wedge. Historical records document multiple eruptions at Pagan in the 20th century, underscoring the close spatial and temporal link between deep seismicity and arc volcanism.

Since 2000, the Pagan region has hosted several earthquakes above magnitude 7.0, highlighting its elevated seismic hazard. Intermediate-depth events such as the 2007 earthquake typically produce limited surface shaking on the islands yet can trigger submarine landslides and local tsunami warnings. The Mariana Trench, located only 150 km to the east, marks the surface expression of the plate boundary and reaches depths greater than 10 km, further concentrating tectonic stress.

Ongoing monitoring by regional seismic networks continues to track microseismicity and volcanic unrest. The combination of deep slab earthquakes and active volcanism defines the Pagan region as a key locality for studying subduction-zone processes and associated hazards in the western Pacific.