Deep Earthquake Activity in the Pagan Region of the Northern Mariana Islands

The Pagan region of the Northern Mariana Islands experienced a significant magnitude 7.7 earthquake on July 29, 2016, at 21:18 UTC. The event occurred at a depth of 267 kilometers, consistent with deep-focus seismicity in subduction zone environments. Two nearly identical magnitude 7.7 events were recorded that day, located within a few kilometers of each other, highlighting the precision limits of early location estimates for deep events.

The Northern Mariana Islands form part of the Mariana volcanic arc, created by the subduction of the Pacific Plate beneath the Philippine Sea Plate. This tectonic setting produces a steeply dipping Wadati-Benioff zone capable of generating earthquakes at depths exceeding 200 kilometers. Pagan Island itself sits above this active subduction system, where intermediate-depth and deep earthquakes occur regularly as the downgoing slab deforms and transforms.

Historical records since 2000 show additional strong events in the same area. A magnitude 7.2 earthquake struck the Pagan region on October 31, 2007, approximately 37 kilometers from the 2016 epicenter. These events illustrate the persistent seismic productivity of the Mariana slab at intermediate to great depths.

Deep earthquakes in this region typically produce limited surface shaking due to their focal depths, though they can be felt across the island chain. The 2016 sequence did not generate a tsunami, as is common for events occurring well below the seafloor. Ongoing monitoring by regional seismic networks continues to track slab-related seismicity to improve understanding of subduction dynamics beneath the Mariana arc.

References

USGS Earthquake Catalog Global CMT Project Earthquake Catalog