P- and S-Wave Seismic Reflection Profiling Across the Kamishiro Fault, Itoigawa-Shizuoka Tectonic Line Active Fault System, Central Japan

Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2,,**1 pp.,/ -/ +, -. / 0 1 2 3 - +* +* ++ +, +- +. +/ +0 +1 - +2 +3,* -,+ + :, -. : / 0 : 1 : 2 3 +* ++ +, +- +. : +/ : +0 : +1 : +2 : +3 :,* :,+ P- and S-Wave Seismic Reflection Profiling Across the Kamishiro Fault, Itoigawa-Shizuoka Tectonic Line Active Fault System, Central Japan Nobuhisa Matsuta + *, Yasutaka Ikeda,, Hiroshi Sato -, Toshifumi Imaizumi., Masami Togo /, Hiromi Yanagi 0, Hitoshi Mikata 1, Shigeru Toda 2, Hiroyuki Tsutsumi 3, Eiji Kurashimo -, Shin Koshiya +*, Ken Noda +*, Hajime Kato ++, Kazuomi Hirakawa +,, Kouji Yagi +-, Masanori Shishikura +., Tomoo Echigo +/, Tatsuya Ishiyama +0, Tsuyoshi Haraguchi +1,Sumiko Ogino -,Yoshimasa Arai +2, Tomonori Kawamura +3,Masayoshi Tajikara,*, Naoko Kato -, Takeshi Ikawa,+ and Kamishiro seismic profiling group + Graduate School of Science, The University of Tokyo (Now at National Taiwan University),, Graduate School of Science, The University of Tokyo, - Earthquake Research Institute, The University of Tokyo,. Faculty of Education and Human Sciences, Yamanashi University (Now at Graduate School of Science, Tohoku University), / Laboratory of Physical Geography, Hosei University, 0 Faculty of Education and Human Sciences, Yamanashi University (Now at Ricoh Technosystems Co., Ltd), 1 Earthquake Research Institute, The University of Tokyo (Now at Dept. of Civil and Earth Resources Engineering, Kyoto University), 2 Aichi University of Education, 3 Graduate School of Science, Kyoto University, +* Faculty of Enjineering, Iwate University, ++ Faculty of Education and Human Sciences, Yamanashi University, +, Faculty of Environmental Earth Science, Hokkaido University, +- Faculty of Education, Yamagata University, +. Graduate School of Science and Technology, Chiba University (Now at Japan Atomic Energy Agency), +/ Graduate School of Science and Technology, Chiba University (Now at Geo-Research Institute), +0 Graduate School of Science, The University of Tokyo (Now at Japan Atomic Energy Agency), +1 Fukken Co., Ltd (Now at Graduate School of Science, Osaka City University), +2 Earthquake Research Institute, The University of Tokyo (Now at Tokyo Electric Power Company), +3 Graduate School of Science, The University of Tokyo (Now at Japan Atomic Energy Agency),,* Earthquake Research Institute, The University of Tokyo (Now at JGI Inc.),,+ JGI Inc. * e-mail: nobumatta@ntu.edu.tw +*0 +- -+2 25

Abstract The Kamishiro fault forms the northern-most part of the Itoigawa-Shizuoka Tectonic Line (ISTL) active fault system. This fault displaced young lake deposits in the Kamishiro basin, and the shallow (less than,* m) structure of the fault and an average long-term vertical slip rate of,.,,.1 m/kyr were revealed by drilling and geomorphological investigations. To reveal the subsurface structure of this fault system and estimate long-term net slip rate, we carried out S- and P-wave high-resolution shallow seismic reflection profiling across the Kamishiro fault. The S-wave seismic line is,** m, the receiver point intervals are + m, and the shot point intervals are, m. We used a +3,- channel seismic system with a mini-vibrator to image the depth range of / to 1* m. The P-wave seismic line is,.+ km, the receiver point intervals are +* m, and the shot point intervals are +* m. We used a +10-channel seismic system with a mini-vibrator to image the depth range of /* to 2** m. From these experiments, it is clarified that the Kamishiro fault cut and fold the lacustrine deposit. The deformation is associated with fault development near the surface. Given the dip angle of the Kamishiro fault determined by S-wave seismic profiling to be approximately -*, the average dip slip-rate is calculated to be... /.. m/kyr. And, the Kamishiro fault corresponds to cutting across the anticline rather than the deformation front on the P-wave seismic profile. The fold is related to blind thrust fault, fold propagation fold, or drag structure. Key words: Itoigawa-Shizuoka Tectinic Line, seismic reflection survey, Kamishiro fault, tip of the fault + Ikeda and Yonekura +320; +321; +33. +332; +332 +331 ; +332 ;,**+ +321,2 ka -.. m kyr,**0 +, + -./ m kyr +331 dip +./ m kyr,** m S,**+ Matsuta et al.,**.... /.. m kyr +330,.* km P S P, Fig. + 26

{7 [} LM ~ B ~ O Fig. +. Geologic setting of the Kamishiro area. (A) Index map, (B) Geologic map of the northern part of the ISTL active fault system after Yamada et al. (+323). Active fault map is modified after Ikeda et al. (,**,), (C) Detailed Geological map around the study area modified from Nagahashi (+332) and Kosaka and Arai (+32,). ῌ +332 ; Sato et al.,,**. 0DEFGH IJ8GH (K ῌ +332 ; Matsuta et al.,,**.!" #!ῌ$!" % LMNO P: Q!,R 58.2ST.UV W &' (%& ῌ )*+ NO X: %&' YZ+[E@2\^' ] F,- %&' )*+./012 ( 345 _`@2 (a7bcdefghi +3/2 \^' X,**, ; 6745 +33/ ;jk/ P58 l m% -** m ;n@2ropqr 5896:;<= >?@2A ;BC stuv (wx +332 y =z; lm% 22* m 27

Fig.,. Location of S- and P-wave seismic lines. Base map is after Hakuba village and geologic map is after Nagahashi et al. (+332). Geomorphological map is after Matsuta et al. (,**0). The tick on the fault is down side. +3/2 +., km, -./ km +322;,**+ +32* +33+; +33/;,**+,**+ - S - + +331 S,**+ S,** m Fig., - Table + Industrial Vehicles International T+/*** GDAPS-. Table +, m +/ +** Hz, +- - P.* Hz - +22 + m + ms, - Fig.. ProMAX Landmark Fig.. CMP P S P S 28

Fig. -. Location of S-wave seismic line and active fault. Base map is after Hakuba village. This seismic line is located beside the drilling point (Matsuta et al.,,**+), the trench site (Okumura et al., +332) and the investigation by the gioslicer (Imizumi et al. +331). Ticks are on down side. Table +. Data acquisition parameters for the S-wave Kamishiro seismic survey and P-wave Kamishiro seismic survey. CMP +/ +** Hz 0* Hz F-K CMP.* CMP +** RMS TWT; Two- Way Travel Time *./ +/* m s TWT +.* s,** m s, TWT *./,/* m/s, TWT +.* s./* m s -.* +./ +** m -, Fig. / Fig. 0,**+ *.. CMP +* +** TWT *.-/,* m *.0/ /* m TWT *.0/ CMP ++* CMP +-/ 29

¹º» Fig... Shot gather at RP +* (a) and processing steps and parameters for the Kamishiro S-wave seismic data (b). Fig. /c CMP,.* -** TWT *./ῌ *.3 Fig. / A Aῌ, [ 60+ QDcIJKD d'nef* M g$& /g h iij "jk Fig. 0 A (! "#$% & ' ( )*+, -. avg,.* km st uv*6 Fig., av @ /&! 0 lm +.2 nv T o ipq r 12 3456 &w eva[xy*6 av + z{ +330 7489 +, : ;< 2=>? @ A avn }-. ( av ~ lm ( Fig. /c B B Fig. /b Bῌ, Fig. 0 B [ + Q N* C &D : ;< 2=>? EFGH* + av ~ Q M : @ A ( Fig. /c C B Fig. /b QL Cῌ+ Fig. 0 C + IJKD L M 3489 N D5 st 3489 c7 A 89 N O*6 PM QDN RS T UV / IJKD av ~5 st Q WX Y*+ IJKD L M QDZ O[\ @ A $+ av ~ IJK av uv# + : ;< 2= >? 4 N* *+!"#D ] a# N P. ^ pjq^ $ Industrial Vehicles. + International ª«T+/*** F [% + _ P D ] Q^_` av IJKD QLOb ±² Q³ jµx «GDAPS-. [ %*6 Ta- ¼ 30 ¼

Fig. /. Filtered stacked section (a) and post stacked, migrated time section (b) of the S-wave seismic line. Fig. 0. Depth converted, S-wave seismic section and its geologic interpretation. 31

r¹º» Fig. 1. Shot gather at RP 1* (a) and processing steps and parameters for the Kamishiro P-wave seismic data (b). ble. + +*ῌ+,* Hz $ -0 "# WX+ x - Fig. 1 hyt z{!"# $ %&'() } ~ ij@a! d Y 20Z % *+, -./0 1 +*ῌ0* Hz 2 30 TWT >Two-Way Travel Time *.0 *./ῌ+ km 45 6 *7-890 :&; J -w!g N g N,* m <=: >RP +** >?@ RP+** -RP,.0 A Z' - G 2d +*ῌ+,* Hz %& +/ h 0Z #Z G 2 N g [ M *+, +* B RP,.2-RP -+. A C N G - G }h + 0Z +*ῌ0* Hz %&,* *+, ' } 7 # A DE- 0 +* B +/ B,* B20 <=: &; +* m,2 Hz <=F" G +10 HIJKL h G 0[ 8 N c N [h a0 MN0 OJ PJQ&;, ms, RS TU - 6 * h q :8 -ª 0 6 * VWX+ SPR WXJ-0 SP >Fig. 1 «5 - G - tg $h R WXJY 6 *- *+,0Z7 0Z[G FK L* -"± 6 *- [ «5 \]?@" ^_0 RP,.0 A +10 HIJKL - `a MN:.2 HIJK L* -q [6 *- 0 6 * h L -ef0g hij0k5 RP -+. "?hlm µ " ProMAX - 0 RMS «5 CMP n RP,.0 A o)`a b MN-c# /* #h 7 -c# d RMS «5 N g b c[ d Y? ' pq r[ 2pstG : uvw ¼ 32 ¼ [Z Normal Moveout!²-tG³h FK CMP +** TWT *., +., km ῌ s, *./

±²³ µ { { { {CD¹1º»¼ Fig. 2. Filtered stacked section (a) and post stacked, migrated time section (b), interpretation on migrated time section of the P-wave seismic line. +.1 kmῌs, +.* -., kmῌs, CMP -** TWT jy>q :klmp> *., +.- km, *./,.+ kmῌs +.* -.* kmῌ r stu vwx ar s } {"<=mp>~ : B MP> N.,, Fig. 3 "/0 UNIT + 7pq UNIT, 7yz ῑ{l CMP +1* R 7 Z[ GC, DH : M!"#$ %&'()*+,- :no, Fig. 2 ". 1234567 Fig. 2c P> GUNIT -H QP7 N \] h 1 12LM ῌr {Y } {LM CD P> 89:. Fig. 3 ";<=0>56,?@0> Reflecter + 7 hyiy> ABCD$E*F GReflector +H :IJK GTWTH *.,/ CMP + LM CMP,** N OMP> QP RS A LM B,r 7 UNIT, UNIT + 0> 9"; RST7 T 7UVWXYZ[,\]0>Q :^ > GUNIT : B GUNIT.H Q 7 s Reflector + R_T 7`Z Z[:OMP>, 0> ª1"ῐ«0>Q LM s,h GUNIT +H b st } { a>~ :a> Reflector + 7ABCD$E*F a> UNIT + UNIT, 7cd$*e'f* :ghi ± 33 ± N UNIT - ob> 9" >Z[7

% ` Fig. 3. Depth converted, P-wave seismic section and geologic interpretation. Unit + : Pre-Neogene, Unit, : Mikaichiba welded tu#, Unit - : late Quaternary fluvial and lacustrine sediments, fault. C, D \ >' CMP +1/! " E CMP,-*! " F # /ῌ ij kb, lc$ =` # M) $ % &$,**0 '( CMP,,/ D )ῌ m ) no A>$ 9 1 # P! CMP,1/! )* + #, - -./HL p S -G,./H.'/0 qr s IJ =` Et u #vw Fig., CMP,1/! 1234 567 # CMP,,/! F<5 ).x/0 = A>$ 8!9 : " CMP,,/! ; #Z>' yg $ 5P/0 D'( # # #< = 8! $ # z0= HI.' $>?@ 8! A =' " E B # % 0 ) )& C, /0 0D'( " E ῑ ῐ #, J/H J{ K$}*~}*{ L M # )5, $ *E9 D'( F+# N ++.2**+3 { O ῌPQ R L pk$} < *~}*{ L MN *1-*2**1 { O ῌPQ G, S -./H IJ 019 G, K L0/BM 2NI 34 R.ST L $ U0. /H# VWXL py $ 5 Z O P/ ) /L $ 5P P/0 0 == / [ Y9 /0 =`./HX 3 =' 67 899 1QR STU Allmendinger, +332 : )# '( O P/2NI M D V \] : PQ R F*^*l{ } _\] : % ` F*^*l{ } QWX ) D'( Y #Z>' X 3 y& a : PQ Rῌ% ` ῌQbc " ;E[ F*F* ^*l{ } de D'( \ >' =' <]^_ P -, /H hi F*^*$ ^* jkl ῌ Q #BZ>' \ >( =` $ 5?@#< Fig. 2c, Fig. 3 ac E! bc>h d ( =` )efg1 2NI34?@# h A>$.' fῌ $ ῌg ῌmM ῌ n4 ῌ XToῌªjp F*.{ 7 «Q q T F* r±²g³ g1 asµk ῌ ªj ῌ,h tῌu vwῌ AῌC ¹ºῌxyz»{F ¼ 34 ¼

Allmendinger, R.W., +332, Inverse and forward numerical modeling of trishear fault-propagation folds, Tectonics, +1, 0.* 0/0. +3/2 0..-+../. +322 -- 0 1. +32* -0-p. +33+.-1p. +32,,,. +2+ +32. Ikeda Y. and N. Yonekura, +320, Determination of late Quaternary rates of net slip on two major fault zones in central Japan, Bull. Dept. Geogr. Univ. Tokyo, +2,.3 0-. +331 +0 -/.-. +332, /*,- --.,**+,* /3 1*. Matsuta, N., Y. Ikeda, and H. Sato, The slip rate along the northern Itoigawa-Shizuoka tectonic line active fault system, central Japan,,**., Earth Planet. Space, /0, +-,/ +--,.,**0,0 +*/ +,*. +332 +*. +2. +32.,**, / + +*/p. +33.,.0.,/.-2. +332, /* -/ /+. +332 02 0-1+. Sato H., Iwasaki T., Kawasaki S., Ikeda Y., Matsuta N., Takeda T., Hirata N. and Kawanaka T.,,**.. Formation and shortening deformation of back arc rift basins revealed by deep seismic profiling across the Itoigwa- Shizuoka Tectonic Line active fault system, central Japan, Tectonophys, -22,.1 /2. +321 +1 3, 3-. +33/ + : +**,*** +321..,.0. +323,* + +330.1-3- -32. Received March 1,,**1 Accepted June,3,,**1 35