Location:

Period:

8 Jul 2022 16:55:13 - 8 Jul 2022 23:43:29 (6 hours 48 minutes)

Volcanoes in 100km radius:

None

Earthquakes:

2 swarms found nearby.

2001

PS20010615.1(10.2km)

14 Jun

6 hours

5 earthquakes

2016

PS20160729.1(141.5km)

29 Jul

20 minutes

5 earthquakes

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Seismic Swarm in the Pagan Region, Northern Mariana Islands: July 2022 Analysis

A seismic swarm designated PS20220708.1 occurred in the Pagan region of the Northern Mariana Islands on 8 July 2022. The sequence began at 16:55 UTC and concluded at 23:43 UTC, lasting 6 hours and 48 minutes. During this period, nine earthquakes were recorded, with magnitudes ranging from 5.0 to 5.9 and focal depths predominantly at 10–12 km.

The events unfolded as follows: a 5.4-magnitude quake at 16:55:13, followed by a 5.3 at 17:02:58, a 5.0 at 17:10:02, another 5.0 at 17:23:46, a 5.0 at 17:46:28, a 5.3 at 20:44:26, a 5.0 at 20:46:11, a 5.8 at 23:36:06, and culminating in a 5.9 at 23:43:29. All events clustered tightly in time and space, characteristic of swarm behavior without a dominant mainshock-aftershock pattern.

The Pagan region lies within the Mariana Volcanic Arc, formed by the subduction of the Pacific Plate beneath the Philippine Sea Plate. This tectonic setting drives frequent seismicity and volcanism across the Northern Mariana Islands. Pagan itself is an active stratovolcano situated on the Mariana Ridge, with documented eruptions in historical times contributing to the area's elevated seismic hazard.

Since 2000, only two prior swarms have been identified in the region: one in 2001 and another in 2016. These infrequent clusters underscore the episodic nature of seismic activity here, often linked to magma movement or fault interactions within the arc system.

This 2022 swarm provides insight into the ongoing tectonic stresses in the subduction zone. The consistent shallow depths and rapid succession of moderate-magnitude events suggest fluid migration or stress transfer along local faults, common in volcanic arcs. Such activity reinforces the need for continued monitoring in this remote but geologically dynamic part of the Pacific Ring of Fire.

References

USGS Earthquake Catalog (earthquake.usgs.gov)
Smithsonian Institution Global Volcanism Program (volcano.si.edu)
Pacific Island Science and Technology (pacificislandsciencetech.org)