Plate Convergence and Block Motions in Mindanao Island, Philippine as Derived from Campaign GPS Observations
Takahiro Ohkura*1, Takao Tabei*2, Fumiaki Kimata*3,
Teresito C. Bacolcol*4, Yasuhiko Nakamura*5, Artemio C. Luis, Jr.*4,
Alfie Pelicano*4, Robinson Jorgio*4, Milo Tabigue*4,
Magdalino Abrahan*4, Eleazar Jorgio*4, and Endra Gunawan*6
*1Aso Volcanological Laboratory, Kyoto University, 5280 Minami-Aso, Aso, Kumamoto 869-1404, Japan
*2Department of Applied Science, Kochi University, Kochi, Japan
*3Tono Research Institute of Earthquake Science, Gifu, Japan
*4Philippine Institute of Volcanology and Seismology (PHIVOLCS), Philippines
*5Graduate School of Integrated Arts and Sciences, Kochi University, Kochi, Japan
*6Graduate School of Environmental Studies, Nagoya University, Nagoya, Japan
We conducted yearlyGlobal Positioning System(GPS) campaigns in the eastern part of Mindanao from March 2010 to March 2014. The obtained station velocities with respect to the Sunda plate (SU) show that WNW motions are dominant due to the convergence of the Philippine Sea plate (PHS). However, it was found that elastic deformations caused by a full coupling of the plate interface down to 80 km could explain a maximum of only 29% of the observed station velocities. In order to interpret the displacement pattern, we applied a rigid block rotation model and determined the Euler vector. As a result, we determined that Mindanao Island could be divided into at least three blocks and that the Philippine fault is one of the block boundaries. Although it was not possible to determine the coupling ratio at the Philippine trench, the dislocation pattern of the Philippine fault showed along-strike variation in Mindanao Island.
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