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Earth, Planets and Space

, Volume 58, Issue 8, pp e33–e36 | Cite as

Crustal structure of the ocean-island arc transition at the mid Izu-Ogasawara (Bonin) arc margin

  • Azusa Nishizawa
  • Kentaro Kaneda
  • Ayako Nakanishi
  • Narumi Takahashi
  • Shuichi Kodaira
Open Access
E-Letter

Abstract

Wide-angle refraction experiments were conducted to reveal the crustal structure at the transition between the intra-oceanic island arc crust of the mid Izu-Ogasawara (Bonin) arc and the backarc oceanic crust of the Shikoku Basin. The island arc crust consists of an upper crust about 5 km thick with a P-wave velocity <6.0 km/s, a middle crust 5 km thick with a P-wave velocity of 6.0–6.3 km/s, and a lower crust 10 km thick with a P-wave velocity of 6.8–7.2 km/s. The total crustal thickness is about 20 km. The thickness thins to approximately 6 km over a distance of 30 km at the western margin of the Izu-Ogasawara arc (IOA). These features are very similar to those of the northern IOA, which indicates that the crustal structure is relatively constant within 200 km at the northern and mid IOA. The Kinan Escarpment, a 500-km-long fault with a maximum offset of 800 m, characterizes the transition zone between the IOA and Shikoku Basin. The seismic crustal model indicates that the escarpment is a fault which tears the whole oceanic crust along the western margin of the IOA. However, no significant differences exist in the crustal structure on either side of the escarpment, and the Kinan Escarpment seems to be a zone of the structural weakness from its birth.

Key words

Mid Izu-Ogasawara (Bonin) arc Kinan Escarpment P-wave velocity structure 

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Copyright information

© The Society of Geomagnetism and Earth, Planetary and Space Sciences (SGEPSS); The Seismological Society of Japan; The Volcanological Society of Japan; The Geodetic Society of Japan; The Japanese Society for Planetary Sciences. 2006

Authors and Affiliations

  • Azusa Nishizawa
    • 1
  • Kentaro Kaneda
    • 1
  • Ayako Nakanishi
    • 2
  • Narumi Takahashi
    • 2
  • Shuichi Kodaira
    • 2
  1. 1.Hydrographic and Oceanographic DepartmentJapan Coast GuardTokyoJapan
  2. 2.Japan Marine Science and Technology CenterYokohamaJapan

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