M 7.1 - 4 km SE of Sagbayan, Philippines

Tectonic Summary

The October 15, 2013, M 7.1 earthquake near the city of Catigbian on Bohol Island, Philippines, occurred as the result of shallow reverse faulting on a moderately inclined fault dipping either to the northwest or to the southeast. Finite-fault modeling of globally recorded seismic data for this earthquake is not able to distinguish between these two possibilities. The depth of the event indicates that it ruptured a fault within the crust of the Sunda plate, rather than on the deeper subduction zone plate boundary interface. At the location of this earthquake, the Philippine Sea plate moves towards the west-northwest with respect to the Sunda plate at a rate of approximately 100 mm/yr, subducting beneath the Philippines several hundred kilometers to the east of the October 15th earthquake at the Philippine Trench.

The Philippines straddle a region of complex tectonics at the intersection of three major tectonic plates (the Philippine Sea, Sunda, and Eurasia plates). As such, the islands frequently experience large and damaging earthquakes, and the region within 500 km of the October 15th earthquake has hosted 19 events of M 6+, a dozen of which have been shallow (0–70 km). One of these, a M 6.8 earthquake 70 km to the east of the October 15, 2013, event in 1990, caused several casualties.

Hayes et al. (2016) Tectonic summaries of magnitude 7 and greater earthquakes from 2000 to 2015, USGS Open-File Report 2016-1192. (5.2 MB PDF)