Seismic Activity in Guam: The 2001 M7.0 and 2002 M7.1 Earthquakes

Guam lies within the tectonically active Mariana subduction zone, where the Pacific Plate converges with and subducts beneath the Philippine Sea Plate at rates exceeding 6 cm per year. This setting produces frequent moderate to large earthquakes, with the island situated on the overriding Mariana Plate near the Mariana Trench. The region’s geology features volcanic arcs, forearc basins, and extensive fault systems that accommodate both subduction-related thrusting and strike-slip motion. On 12 October 2001 at 15:02 UTC, a magnitude 7.0 earthquake struck 69 km south-southeast of Inarajan Village at a depth of 37 km. The event was centered within the forearc region and produced strong ground shaking across southern Guam. One year later, on 26 April 2002, a magnitude 7.1 earthquake occurred 20 km south-southwest of Merizo Village. Its epicenter lay approximately 59 km from the 2001 rupture zone, highlighting the clustered nature of large events along the plate interface and nearby crustal faults. Both earthquakes exemplify the persistent seismic hazard in the southern Mariana Islands. Historical records document repeated M7+ events throughout the twentieth century, reflecting the ongoing accumulation and release of strain along the subduction megathrust and secondary faults. Depths between 30 and 40 km, as recorded for the 2001 shock, are typical of intraslab or interface earthquakes in this segment of the subduction zone. The proximity of the two recent events underscores the potential for temporally clustered seismicity. Guam’s population centers, infrastructure, and coastal exposure remain vulnerable to strong shaking, tsunami generation, and secondary hazards such as landslides. Continued monitoring by regional seismic networks supports improved understanding of rupture patterns and long-term hazard assessment for the island.

References

USGS Earthquake Catalog (events 2001-2002). Global CMT Project focal mechanism solutions.