High-resolution seismic reflection profiling across the Senya fault at Hanaoka, northern Honshu, Japan: Data acquisition and processing

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1 Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2+,**0 pp. 31 +*0 : + *, -. / * , , - :. : / * ++ : +, : +- : +. High-resolution seismic reflection profiling across the Senya fault at Hanaoka, northern Honshu, Japan: Data acquisition and processing Hiroshi Sato + *, Yasutaka Ikeda,, Toshifumi Imaizumi -, Hitoshi Mikada., Shigeru Toda /, Hiroyuki Tsutsumi 0, Shin Koshiya 1, Ken Noda 1, Tanio Ito 2, Takahiro Miyauchi 2, Hiroshi Yagi 3, Masami Togo +*, Takaya Iwasaki ++, Mamoru Saka +, Naohsi Hirata +, Nobunao Matsuta ++, Tomonori Kawamura +,, Kouson Ishimaru +-, Takeshi Ikawa +. and Senya 30 Seismic profiling group + Earthquake Research Institute, The University of Tokyo,, Graduate School of Science, The University of Tokyo, - Faculty of Education and Human Sciences, Yamanashi University (Now at Graduate School of Science, Tohoku University),. Earthquake Research Institute, The University of Tokyo (Now at Graduate School of Engineering, Kyoto University), / Aichi University of Education, 0 Graduate School of Science, Kyoto University, 1 Department of civil & Environmental Engineering, Iwate University, 2 Department of Earth Sciences, Chiba University, 3 Faculty of Education, Yamagata University, +* Hosei University, ++ Graduate School of Science, The University of Tokyo (Now at National Taiwan University), +, Graduate School of Science and Technology, Chiba University (Now at JGI Inc.), +- Power Reactor and Nuclear Fuel Development Corporation (Now at Japan Atomic Energy Agency), +. JGI, Inc. Abstract The Senya fault, northern Honshu, Japan, which generated the Rikuu earthquake (Mj 1.,) +230, is a typical intra-arc active thrust. Subsurface geometry provides essential information for better understanding strong ground motions and crustal deformation processes. A high-resolution seismic reflection survey was conducted along the 0-km long seismic line across the toe of the thrust to reveal the subsurface geometry. The seismic source was a Mini-vibrator truck and the receiver interval was +* m. The seismic data were processed by the standard common mid-point method. The Senya fault is clearly identified as a boundary between horizontal reflectors of the basin fill in the Yokote basin and moderately dipping reflectors beneath the Senya hills. The thrust occurred in late Miocene mudstone, and shows a flat and ramp geometry. The emergent thrust dips -* degrees down to /** m, and changes its dip to subhorizontal following the distribution of the mudstone. * satow@eri.u-tokyo.ac.jp ++- **-,

Key words: active fault, seismic reflection profiling, Senya fault, Rikuu earthquake, Northern Japan + +230 Mj 1., +230 Nakata, +310; Ikeda, +32-; +32* +320 +330 2 Sato et al.

2 Key words: active fault, seismic reflection profiling, Senya fault, Rikuu earthquake, Northern Japan Mj 1., +230 Nakata, +310; Ikeda, +32-; +32* Sato et al., ,**,, Sato, +33. Fig. + Sato et al.,,**,, Fig., , + +31/ / Fig., Fig. +. Generalized geological structure of northern Honshu (modified after Yamazaki et al., +32-). 98

Fig.,. Geological map around the Senya hills showing the location of the Senya 30 seismic line. The geological map is after Usuta et al. (+310) modified by authors based on new geological survey.

3 Fig.,. Geological map around the Senya hills showing the location of the Senya 30 seismic line. The geological map is after Usuta et al. (+310) modified by authors based on new geological survey ,AC+., Fig., /** m +230 Mj 1., +32,;,**- -./ m -m +230; +32* - 0 km Fig. - Table + IVI T+/***; +330 JGI, G daps., msec, +2*,2 Hz 3 +* m,,* m +* +,* Hz,* +* 0* +,* 0* 0* -0 Fig. / ,1 2 2 RP +.* RP./* 99

$Data acquisition parameters for the Senya 30 seismic line. M/(NO P: QR STUVWIX< Y CMP U.Z[ \]^ _`. @ab QR ; % CMP sort.j,fig. -- c do _ e<fdgh.ijkl'ab,pre- ﬁlter-.m! Pn ﬁrst break suppression, gain recovery, whitening deconvolution.$ j o p q Vrst @ uv v jwx yz{.y$ yz }z,-** m/s-.~ z,+,2**,,1** m/s- N @ q.wxm! <.J F /** m N.J ' ub,fig. /-. h! NMO q.j o ' ub. }! Y.Mu F +/ῌ+** Hz C 'AB.m! Mu.! Pn D. Z?@ x fox N v u.

j o p q Vrst @ uv v jwx yz{.y$ yz }z,-** m/s-.~ z,+,2**,,1** m/s- N @ q.wxm! <.J F /** m N.J ' ub,fig. /-. h! NMO q.j o ' ub. }! Y.Mu F +/ῌ+** Hz C 'AB.m! Mu.! Pn D. Z?@ x fox N v u.

4 ¹S º» Fig. -. Detailed location of the Senya 30 seismic line. The base map is at a scale of + :,/,*** issued from the Geographical Survey Institute. phase correlation F GH IJK: SEGY 'L Table +. Data acquisition parameters for the Senya 30 seismic line. M/(NO P: QR STUVWIX< Y CMP U.Z[ \]^ QR ; % CMP sort.j,fig. -- c do _ e<fdgh.ijkl'ab,pre- filter-.m! Pn first break suppression, gain recovery, whitening deconvolution.j o p q uv v jwx yz{.y$ yz }z,-** m/s-.~ z,+,2**,,1** m/s- q.wxm! <.J F /** m N.J ' ub,fig. /-. h! NMO q.j o ' ub. }! Y.Mu F +/ῌ+** Hz C 'AB.m! Mu.! Pn D. Z?@ x fox N v FX prediction filter.m! O.J % h! O y Fig.. % Table, datum correction.!! " #$!% Mer- cury International Technology Co. Ltd. &'()*+ ixl,ver...,-. /(, ª I «<@ < n: FMu. Fig. 0. Fig. 1! &'()*+ Super X. 89 : ; %#<". =.>?@,CMP+ῌ-.*- N ±n 'A BC" A DE. minimun ² %³ µ /( n:@ 9 /** ¼ 100 ¼

5 Fig... Generalized processing flow chart for the Senya 30 seismic line. m +./,./ km/s /** m,./. km/ s.,ac-+. ; Fig., /** m +310 Fig. 2 1** m CMP/-* 2/* 2** 3** m emergent thrust Fig. 2 P CMP.** 0** Sy ; Fig. 2 CMP/-* 10*,**.** m F,; Fig. 2 F, CMP/,* 0** growth strata; Fig. 2 CMP/** 02*,** m Sy,; Fig. 2 CMP/** //* piggy-back basin km/s CMP02* F-; Fig. 2 /** m Fig

6 Fig. /. Optimum stacking velocities determined by velocity analysis and distribution of number of folds along a CMP stacking line. Table,. Processing parameters for CMP Senya 30 seismic line. emergent thrust./.* + km +- km -* Sato et al.,,**, / +230 M 1., 1 30 : : : 102

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10 Chrisitne Orgren +333 :,1 / ++. Ikeda, Y., +32-, Thrust-front migration and its mechanism: Evolution of intraplate thrust fault systems, Bull. Dept. Geogr., Univ. Tokyo, +/, +,/ +/3.,**,,/. p., +31/.2 +32* +230 // 13/ 2//. Nakata, T., +310, Quaternary tectonic movements in Central Tohoku district, Northeast Japan, Sci. Rep. Tohoku Univ., 1th Ser. (Geography),,0,,+-, / +** +*/. Sato, H., Ikeda, Y., Imaizumi, T., Mikada, H., Tsutsumi, H., Koshiya, S., Togo, M., Toda, S., Kawamura, T., Matsuta, N., Yanagi, H., Itoh, T., Miyauchi, T., Orgren, C., Shishikura, M., Suzuki, H., Soeda, Y., Noda, K., Yagi, H., Kumamoto, T., Hirata, N., Iwasaki, T., Saka, M., Ichinose, Y., Aoki, Y., Shimizu, N., Ishimaru, K., Sakai, R. and Ikawa, T., +331, Evolution of the active Senya thrust fault, northern Honshu, Japan, Abstract of Annual Meeting, Seismological Soc. Japan, No.,, Sato, H., +33., The relationship between late Cenozoic tectonic events and stress field and basin development in northeast Japan, J. Geophys. Res., 33,,,,0+,,,1.. Sato, H., Hirata, N., Iwasaki, T., Matsubara, M. and Ikawa, T.,,**,. Deep Seismic Reflection Profiling across the Ou Backbone Range, Northern Honshu Island, Japan. Tectonophysics, -//,.+ /, *,.,**-.+0,**+.3- p / + 1* p. +32, M 0.* : +22/ +32* /1.* /* : /**,*** Received January +/,,**1 Accepted February 3,,**1 106

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