地震 第2輯
Online ISSN : 1883-9029
Print ISSN : 0037-1114
ISSN-L : 0037-1114
GPS観測に基づくフィリピン海プレートの相対運動と西南日本のテクトニクス
小竹 美子加藤 照之宮崎 真一仙石 新
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1998 年 51 巻 2 号 p. 171-180

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The Euler vector of the Philippine Sea plate relative to the Eurasian stable craton was estimated using the Global Positioning System observations. For this purpose, we used repeated observation data at Okino Torishima (Parece Vera) and velocity vectors at some sites on the Philippine Sea plate in the nationwide continuous monitoring network by the Geographical Survey Institute. First, GPS data at Okino Torishima for the period of 1995-1997 were reanalysed taking its reference at Tsukuba IGS site (TSKB). Then, the obtained velocity was converted taking local velocity of Tsukuba relative to the stable Eurasian plate estimated by HEKI (1996) into account. Obtained velocity vector was then combined with Minami Daito-jima, Chichijima and Hachijo-jima velocity data to estimate the Euler vector using the linear least squares method. The estimated location of the Euler pole was (41.55±0.42°N, 152.46±0.57°E) and the anguler velocity was -1.50±0.04deg/my taking counterclockwise rotation as positive. Based on this estimated Euler vector, we discussed the tectonics along the Suruga trough and Ryukyu trench region as the followings: (1) Motions of northern Izu-Bonin islands such as Izu Oshima and Miyake-jima that resembles the plate motion are significantly affected by local motions which presumably be volcanic origin, (2) Directions of slip vectors for the interplate large earthquakes [SENO et al. (1993)] and the azimuth of subducting plate motion show significant offsets of about 10 degrees at the Nankai trough region. This offset might be due to the eastward motion of the Eurasian continent. (3) At the southwestern islands region, rifting of the Okinawa trough is predominant and the Okinawa ridge moves almost toward the opposite direction of the subduction. (4) Two small Taiwanese islands east of Taiwan mainland show significantly slow displacement rates as estimated from the rigid motion model, which might be due to compressional force due to continental collision at Taiwan island.

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