The Ryukyu arc (琉球弧, Ryūkyū-ko) is a volcanic island arc system of Japan's triple junction formed by the subduction of the Philippine Sea Plate beneath the Eurasian Plate between Ryukyu Trench to the south-east and the Okinawa Trough to north-west. It comprises the entirety of the Ryukyu Islands chain. The Ryukyu and Southwest Honshu arcs together form the southwest trending arm of the Boso Triple Junction.
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Ryukyu arc Wikipedia(Text) CC BY-SA