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Earth Planets Space, Vol. 54 (No. 11), pp. 1033-1038, 2002

Deep structure of the Nagamachi-Rifu fault deduced from small aperture seismic array observations

Kazutoshi Imanishi, Hisao Ito, Yasuto Kuwahara, Yutaka Mamada, Takanobu Yokokura, Naomi Kano, Kazuo Yamaguchi, and Akiko Tanaka

GSJ/National Institute of Advanced Industrial Science and Technology, AIST Tsukuba Central 7, 1-1, Higashi 1-Chome, Tsukuba-shi, Ibaraki-ken 305-8567, Japan

(Received December 28, 2001; Revised June 4, 2002; Accepted June 4, 2002)

Abstract: A seismic reflection survey using both explosives and vibrators was conducted in June 2001 around the Nagamachi-Rifu fault, northeastern Japan. We carried out observations of four small aperture seismic arrays in the area to reveal detailed structures of the fault. Array analysis was applied to waveform data from 15 explosives to obtain P-wave scatterer distributions in the area. The obtained P-wave scatterer distribution correlates in space with microearthquake activities and heterogeneous structures such as S-wave reflectors, a structure of caldera, and Mohorovicic discontinuity. We could also image that a sub-horizontal layer with a length of about 10 km exists in the deep extension of the Nagamachi-Rifu fault beneath the seismogenic layer.


Corresponding author E-mail: imani@ni.aist.go.jp


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