The Izu-Bonin volcanic arc results from the subduction of the Pacific Plate beneath the Philippine Plate. It is sometimes called the Izu-Bonin-Mariana Arc, extending for about 1200 km long, with a width of about 400 km. The thickness of the arc is over 20 km (Takahashi et al., 1998). It forms the eastern half of the Paleo- Izu-Bonin Arc. Back-arc spreading caused the Paleo-Izu-Bonin Arc to divide into the present Izu-Bonin Arc and the Kyushu–Palau Ridge, and to form the Philippine Sea Plate between the Paleocene and the Miocene. Seismic imaging suggests that most of the present Izu-Bonin Arc crust was created during Eocene–Oligocene time (Kodaira et al., 2008, 2010). A Paleogene–Neogene volcanic arc forms the basement of the Izu-Bonin Arc, overlain by Quaternary volcanic and sedimentary rocks.