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Seismic structure of the northern end of the Ryukyu Trench subduction zone, southeast of Kyushu, Japan


P-wave velocity models related to the Philippine Sea plate subduction have been obtained from seismic explorations at the northern end of the Nansei-Shoto (Ryukyu) Trench. Both multi-channel seismic reflection and ocean bottom seismographic records provide clear images of the rough seafloor topography and irregular P-wave velocity structure of the northwestern extension of the Kyushu-Palau Ridge and Amami Plateau below the landward trench slope. Low velocity (V p ≤ 4–5 km/s) and thick (>7 km) materials above the plate boundary characterize the landward trench slope structure. An exception to this is found where the subducting plate contacts higher velocity (V p > 5 km/s) materials of the landward plate at the estimated position of the seismic asperity of 1968 Hyuganada earthquake (Mw 7.5).


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Correspondence to Azusa Nishizawa.

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Nishizawa, A., Kaneda, K. & Oikawa, M. Seismic structure of the northern end of the Ryukyu Trench subduction zone, southeast of Kyushu, Japan. Earth Planet Sp 61, e37–e40 (2009).

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Key words

  • Marine seismics
  • Ryukyu (Nansei Shoto) Trench
  • Kyushu-Palau Ridge
  • Philippine Sea plate subduction