Mindoro, Philippines Earthquake

First Posting | Summary
Posting Date: October 8, 2004, 10:30:00 AM

A M6.5 earthquake struck Mindoro Island, Philippines, on Friday, October 8, 2004, at 11:35 p.m. local time (14:35 UTC). The U. S. Geological Survey (USGS) has estimated the focal depth at about 118.2 km. The epicenter was located about 90 km south southwest of Manila, about 45 km west northwest of Batangas, 75 km northwest of Calapan, and 115 km south southeast of Olongapo. The quake was felt over a wide area, including almost 144 km north of Manila. This event occurred in the southern end of the Manila subduction zone where the South China Sea subducts beneath the Philippine Islands to the east. The Manila subduction zone is one of the major subduction zone systems surrounding the Philippines. The total convergence rates between South China Sea and Luzon of northern Philippine range from 6 cm/yr to 9 cm/yr. The crust rapidly thickens at the southeastern margin of the South China Sea. Because of the thickened crust, the subduction zone at the Manila trench terminates in the Mindoro area and is replaced with a collision zone. The current event occurred just at the transition of the subduction zone to the collision zone. Many of the historic events in the area occur in the depth range of 100 to 150 km. Events in this area are likely related to the tears in the subducting slab at the edge of the subduction zone. The largest historic event to have occurred in this region is the 1994 M7.1 Mindoro earthquake, which occurred about 50 km southeast of the current event and caused significant damage in Mindoro. But the 1994 event was a relatively shallow crustal event that occurred in the collision zone. Another event of magnitude M7.9 occurred about 45 km southwest of the current event. That event was likely an interface event occurring in the Manila subduction zone. Overall the seismicity in the southern segment of the Manila subduction zone is more active than its central segment because of the high heat flow in the central segment of the Manila trench. Confirming AIR’s expectations and because this earthquake was such a deep event, no major reports of serious injuries or major damage were reported. Using the available information about the seismological parameters of this event, the AIR earthquake team expects insured losses to be minimal.

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Posting Date: October 8, 2004, 10:30:00 AM