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High-resolution seismic reflection profiling across the
Shiraiwa fault, eastern margin of the Yokote basin
fault zone, northeast Japan : data acquisition and
processing
Kyoko Kagohara+)*, Toshifumi Imaizumi,�, Tomoo Echigo-�, Takahiro Miyauchi.�, Shin
Koshiya/�, Masaru Noda/�, Hajime Kato0�, Shigeru Toda1�, Tatsuya Ishiyama2�, Hiroshi
Sato3�, Shinsuke Okada+*�, Satoshi Kanda++�, Naoto Kamiya++�, Nobuto Morishita,�, Shuichi
Takahashi,�, Kosuke Hashimori,�, Satoko Shimizu+,�, Kota Yamazaki+-�, Taro Koike+.� and
Takeshi Ikawa+.�
+�Graduate School of Science, Tohoku University, ,�Graduate School of Science, Tohoku University,-�Graduate School of Science, the University of Tokyo (Now at Geo-Research Institute), .�Graduate
School of Science and Technology, Chiba University, /�Faculty of Engineering, Iwate University,0�Faculty of Education and Human Sciences, Yamanashi University, 1�Faculty of Education, Aichi
University of Education, 2�Active Fault Research Center, National Institute of Advanced Industrial
Science and Technology, 3�Earthquake Research Institute, the University of Tokyo, +*�Graduate
School of Science, the University of Tokyo, ++�Graduate School of Engineering, Iwate University,+,�Faculty of Science, Tohoku University, +-�Faculty of Education, Aichi University of Education
(Now at TSUDA INDUSTRIES CO., LTD.), +.�Geosys Inc.
Abstract
The eastern margin of the Yokote basin fault zone extends about /0 km at the western foot of
the Ou Backbone Range, northeast Japan. The Rikuu earthquake (Mv1.,) occurred in the Ou
Backbone Range (Mahiru Range) on -+st August, +230. Associated with this earthquake, four thrust
faults-Obonai, Shiraiwa, Ota, and Senya fault- appeared on the surface of the western foot of the
Mahiru Range. These faults were highly sinuous with numerous gaps and en echelon steps.
We conducted a high-resolution seismic reflection profiling survey across the Shiraiwa fault.
The obtained seismic reflection data were processed by conventional common mid-point methods,
post-stack migration, and depth conversion. The subsurface structure across the Shraiwa fault is
characterized by branched low-angle reverse faults and conjugate back-thrust. The emergent
thrust associated with the +230 earthquake is regarded to be a subsidiary reverse fault.
M o E F R w xBull. Earthq. Res. Inst.
Univ. TokyoVol. 2+ I,**0� pp. +,3�+-2
* e-mail : d*-*[email protected] Iy32*�2/12 z{|}T~���}T 0�-�
� 129�
Key words : Riku-u earthquake, Shiraiwa fault, thrust fault, subsurface structure, high-resolution
seismic reflection profiling
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Active faults are after Ikeda et al. (,**,) (B) Simplified geological map in and around the Yokote basin. Surface
geology is compiled from Usuda et al.(+310, +311, +32*), Osawa and Suda (+32*) and Osawa et al. (+322).
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Fig. ,. Location map of the Kotaki ,**/ seismic line and CMP stacking line.
Table +. Data acquisition parameters for the Kotaki
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frequency.
A. Sweep frequency +*�2* Hz.
B. Sweep frequency +*�+** Hz.
C. Sweep frequency +*�+,* Hz.
Fig. .. Flow chart of data processing.
Table ,. Processing parameters for the CMP of the Kotaki ,**/ seismic data.
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Table -. First break mute parameters for the CMP of
the Kotaki ,**/ seismic data.
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Table .. Post NMO mute parameters for the CMP of the Kotaki ,**/ seismic data.
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