An Estimate of the Philippine Sea Plate Motion Derived from the Global Positioning System Observation at Okino Torishima, Japan

Kato Teruyuki, Kotake Yoshiko, Chachin Toshikazu, Iimura Yuzaburo, Miyazaki Shin-ichi, Kanazawa Teruo, Suyehiro Kiyoshi

doi:10.11366/sokuchi1954.42.233

Okino Torishima (Parece Vela) is an isolated island located in the midst of the Philippine Sea plate. Different from other islands in the plate, the island is not contaminated by either local volcanic activity or non-rigid deformation near plate boundary. Thus, monitoring of its displacement may represent rigid motion of the plate. A series of GPS observations at this island with other peripheral sites have been conducted since 1989. We have analysed recent data of 1992, 1944, 1995 and 1996, since precise orbits are available only for these observations. Tsukuba was assumed to be moving according to ITRF93 velocity field. Displacement of Okino Torishima by this assumption suggests that the island is moving toward WNW with a rate of Vns=1.08(±0.81)cm/yr and Vew=-2 .77(±1.04)cm/yr or 2.97(±1.07)cm/yr toward N68.7(±16.1)°W. Taking recent estimate of local velocity of Tsukuba relative to the stable Eurasian plate by Heki (1996) into account, the velocity of Okino Torishima relative to Eurasian craton is estimated to be Vns=3.00(±0.84)cm/yr and Vew=-5.17(±1.06)cm/yr. This result is well consistent with the velocity estimated from seismic slip vectors by Seno et al. (1993) (Vns=2.87 cm/yr, Vew=-5.81 cm/yr). The present result seems to suggest that the Philippine Sea plate is moving steadily at least in the recent hundreds of years.

An Estimate of the Philippine Sea Plate Motion Derived from the Global Positioning System Observation at Okino Torishima, Japan

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