[S08-1] Paleoseismology and paleotsunami studies: Their potential and limitation I

[S08-1-04] Late Quaternary Faulting Along the Different Segments of the Philippine Fault in Mindanao Island, Philippines

^○Jeffrey Perez¹, Hiroyuki Tsutsumi² (1.Philippine Institute of Volcanology and Seismology - Department of Science and Technology (PHIVOLCS-DOST), Quezon City, Philippines, 2.Department of Geophysics, Kyoto University, Kyoto, Japan)

invited

The Philippine fault is one of the most active tectonic structures in the western Pacific region that has generated at least 10 surface-rupturing earthquakes in the past 400 years. This sinistral strike-slip fault, with a length of about 1250 km, traverses the entire Philippine archipelago from northwestern Luzon in the north to eastern Mindanao Island in the south. Consisting of several segments, this arc-parallel and NNW-trending fault is related to the oblique subduction of the Philippine Sea plate beneath the archipelago.

In Mindanao Island, the Philippine fault traverses the eastern portion of the island for about 320 km. It is characterized by fault parallel ridges, systematic deflection of streams and fluvial terraces, sag ponds and tectonic scarps related to historical surface rupture. Based on tectonic geomorphic mapping using aerial photos and field surveys, the Philippine fault in Mindanao is divided into at least nine geometric segments separated by geometric discontinuities like dilatational steps and branching. In terms of its activity, at least two historical surface-rupturing earthquakes have been documented such as the 1879 M7.4 Surigao earthquake and the 1893 M7.3 Monkayo earthquake. Paleoseismic investigations conducted along the different segments in Mindanao also revealed multiple faulting events during the late Quaternary.