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Earth Planets Space, Vol. 61 (No. 8), pp. e37-e40, 2009

E-LETTER

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

Azusa Nishizawa, Kentaro Kaneda, and Mitsuhiro Oikawa

Hydrographic and Oceanographic Department, Japan Coast Guard, Tokyo 104-0045, Japan

(Received June 12, 2009; Revised September 4, 2009; Accepted September 6, 2009; Online published September 30, 2009)

Abstract: 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 (Vp ≤ 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 (Vp > 5 km/s) materials of the landward plate at the estimated position of the seismic asperity of 1968 Hyuganada earthquake (Mw 7.5).
Key words: Marine seismics, Ryukyu (Nansei Shoto) Trench, Kyushu-Palau Ridge, Philippine Sea plate subduction.


Corresponding author E-mail: azusa@jodc.go.jp


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