Poster of the Sulangan, Philippines Earthquake of 31 August 2012 - Magnitude 7.6

Tectonic Summary

The August 31, 2012 M 7.6 earthquake off the east coast of the Philippines occurred as a result of reverse faulting within the oceanic lithosphere of the Philippines Sea plate. The preliminary location of the earthquake indicates this is an intraplate event, 50 or more kilometers to the east of the subduction zone plate boundary between the Philippine Sea and Sunda plates. At the latitude of the earthquake, the Philippine Sea plate moves west-northwest at a velocity of approximately 100 mm/yr with respect to the Sunda plate.

While this region of the Philippines experiences moderate-to-large earthquakes fairly frequently - there have been approximately 40 events of M6 and above over the past 40 years, within 250 km of the August 31 2012 earthquake - large events outboard of the subduction zone are unusual. While several moderate-sized events have occurred in this intraplate region, most have been the result of normal faulting within the shallower oceanic lithosphere, rather than deeper reverse faulting like August 31 2012 event. The largest nearby event regardless of mechanism was the October 1975 M 7.6 earthquake, approximately 200 km to the north of the August 31 2012 event.

Earthquake Report

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