Seismic Reflection Profiling Across the North of the Itoigawa-Shizuoka Tectonic Line in Omachi, Central Japan

Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2,,**1 pp. -1.. +, -. / - 0-1 2 3 +* ++ +,, +- + :, -. : / : 0 : 1 2 : 3 +* ++ : +, : +- Seismic Reflection Profiling Across the North of the Itoigawa-Shizuoka Tectonic Line in Omachi, Central Japan Nobuhisa Matsuta + *, Yasutaka Ikeda,, Hiroshi Sato -, Toshifumi Imaizumi., Masayoshi Tajikara /, Eiji Kurashimo -, Tomonori Kawamura 0, Naoko Kato -, Shigeru Toda 1, Miyuki Tani 2, Hajime Kato 3, Masami Togo +*, Yousuke Nakamura ++, Tomoo Echigo +,, Atsuhiko Tanaka,, Takeshi Ikawa +- and Omachi 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), / Graduate School of Science, The University of Tokyo (Now at Japan Atomic Energy Agency), 0 Earthquake Research Institute, The University of Tokyo (Now at JGI Inc.), 1 Aichi University of Education, 2 Aichi University of Education (Now at Institute for Geo-Resources and Environment, National Institute of Advanced Industrial Science and Technology), 3 Faculty of Education and Human Sciences, Yamanashi University, +* Laboratory of Physical Geography, Hosei University, ++ Graduate School of Science, Kyoto University (Now at Faculty of Geo-environmental Science, Rissho University), +, Graduate School of Science and Technology, Chiba University (Now at Geo-Research Institute), +- JGI Inc. Abstract The Itoigawa-Shizuoka tectonic line (ISTL) active fault system poses the highest seismic risk, and shows one of the largest slip rates among active faults on Honshu Island. In the Omachi area, the ISTL active fault system comprises the eastern Matsumoto basin (EMB) fault to the west and the Otari-Nakayama fault to the east. To understand the structural relation between these two faults, we conducted a seismic reflection survey across them. The length of the seismic line is 0.. km, and the receiver and shot point intervals are +* m. We used a mini-vibrator as a seismic source with a +2*-channel seismic recording system. We can image the structure to less than about + km in depth. The seismic depth section displays the EMB fault as a boundary between east-dipping reflectors to the east and horizontal reflectors in the Masumoto basin. The EMB fault is interpreted as an east vergent, emergent thrust, and its deeper extension merges with the Otari-Nakayama fault. The * e-mail: nobumatta@ntu.edu.tw +*0 +- -+2 37

Omine Formation, which was laid down on an alluvial fan in the late Pliocene and the early Pleistocene, is distributed between EMB and Otari-Nakayama fault. It is evident that the thrust front migrated from the Otari-Nakaya fault to the EMB fault in Quaternary, and then the Omine Formation located at the foreland basin was uplifted. Key words: Itoigawa-Shizuoka Tectinic line, seismic reflection profiling, Omine Formation, thrust front migration, Eastern Matsumoto Basin fault + +32-; +32-; +332 +330 -* 2 Okumura,,**+ +323 Arai,*** Fig. + +32*,***,*** 0.. km Matsuta et al.,**., +323; Fig. + +332; Sato et al.,,**. +33+,*** +32- +332 +.0/ Ma +331 +331 Arai,*** +32- Arai,*** 38

µq ¹ º» ¼ Fig. +. Geologic setting and location of the study area. A) Index map, B) Geological map along the northern part of the Itoigawa-Shizuoka tectonic line. Geological map is after Yamada et al. (+323) and active faults are after Ikeda et al. (,**,). # ] n )? ~ RP -**!" b c 9 RP -**!"X] } k ] - p bc2) 9 ] p JR!"#$%&' () 0.. km * + N* G U n * k =KL) Z~ Y RP -**!"#$ RP -0*!" Fig., 12,- 3 # M bc 9 RP -0*!"#$ RP /-* 4 5678 9 4 :;2)<=>?@!" k @# 9 RP /-*!"#$ A7BCDE FG 9 HIJCDKLMN) OPQ } k >?`X p u k =KLMN) R#9 +33/ ; SR#9 +333 ; R#9,**0T!" RP //*!"#$ RP /**!" k / G,-. /0 U VWQ X)YZ[\ X]^_ M`]9 a 2) N bc def ORPT /3* g!"ghi$l) N R# O,**0T XLj9,-k +ῌ, lm.= KL. n +/ m opqb M`]9 rsz ªC5G M«KL)G KL) [\#$ 8± ~.=2)? { 9 %&' }n 1** m k~!" }n 1+* m k ]9 O 9 +332T9 ~!" n ]9 Pb t uvqbwx *.2ῌ+./ mmῌyr opgyzkl) n 3-* m, n M`]9 ~ X] Y ² ] ³G ) a 9 KL9 :;@ bcn 39

º¹a» ¼ Fig.,. Geological and geomorphological map showing the location of seismic survey line. Topographic map is modified by Geographical Survey Institute. Geologic map is after Kato et al. (+323). Geomorphologic features are after Sawa et al. (,**0) Table +. Data acquisition parameters for the Omachi seismic survey. Arai,*** RP +1* CMP -**! "# $ %& '( )* +** CMP +1* +,-.! / RP 0! 1 & %& '(/23+,-.! "# $.ῌ ῒ ΐῑ ῐ 4 5& 678 9 2 :; < /=>?@ABC DE* ῌ FGH D IJK9 LMNOP Fig., Q R STUVWXYZ +B [\ * *]^_ UVW I ` a b c [\ *] dnuvw XYZ IJ e fg dh h &11h ij k E* lmno R3 pqrmn Table + s < ; / 3 E, E +2* Z/ t u v <wxyy IVI z{ T+/*** }~!E* :; M +* m V Xmn/! v wxy{ M, ms, -. - ( lmn @A ª GDAPS-. /!E* < M +* m m Xm /E ª Xm «lmn/ n@ " & I # $ %& *] +*ῌ2* Hz E o E* < '] k E* m M +/ ( ),* ( ` /E ±E* ²0/³1E </ 0* n@ / :; k E Z ±E* µ +2* ` [\ 1 * \ + D ) Z /2 E` 0* Z 3 => ῌ n N!E* :; +* Hz : 23 45/E* R ` 967 ¹ - 40 - Z 2µ 0*

³ µ ¹º?»Ly¼6 * 5y 8 ij Fig. -. a) Shot gather at RP-+/ and b) processing flow and parameters for the Omachi seismic data. R ;O RMS s! CMP 89:; ' <=>? @ AB C D( EF>?GH I, <=J 3* K 8L MN K - ( Fig. -, O P QR S -T U 8 1CMP2 <= bc d7erzo f *>? 0 <=L <=*}9~ R ;O `, 0 L Fig.. <=>? n,-h ( 8 & r )!L + (,, MN,, V, WXYRZ [\ ]^ _`,a! '( ), s! H / 1TWT ; Two-Way Travel Time2 *.2 345 67 s! 0 Fig. -! "# $%& '( ) *+,-. /0, 2/ 1Fig. /2 8 b K - - erz. / R ;~erz V, Mercury International Technology 1MIT2 gh 1Fig.,2 erz erz RP 3* 3 8 ijerzbc kp PlmR ixl 1ver. K (! 1** m 10 /* m2..,2 H <=>? n R o 1 ª «2 t( 1**ῌ+,,** m 1 4p _q >? EF r K NMO V m2 1 ª Kv( ) 4! +,/** m 1 1/* RMS s! s!<= s!/j ",a m2 & ± y & ( 2**ῌ3** m 1 /*ῌ, #tuv CMP+** $ wx,( Ly3% +/* m2( z {& CMP /* $ #tuv }9~ L² ( +,** m 3 1./* m2 45yῌ 41 /*ῌ -/* +,+**ῌ+,,** m 1 -/*ῌ./* m2 3

¹º» ¼ Fig... a) Filtered stacked section and b) post stacked migrated time section of the Omachi seismic line. Fig..b! CMP + " '()%*+ 2/*ῌ3/* #$!vpw%- x%y^ 75%z { Fig. /! 23" 2 % & },* w!l CMP -** #$%"& *.. %789C )%, -./0 N Fig..b!./*+ 89 b \ "& CMP -**ῌ.,* #$ *., '( -1 23 *., '( 4! 56" 789!:;./*+./0 E~C./0 89 23! < < 89!S L CMP +*/* #$ 23$! 7%89C => CMP -** 76 =?./*+% @ :./0 2? -./0 2? C ABC L 2 % 27 CMP +*/* #$V CMP -** #$ )1DE!./*+ -1=> 23!FG 2H 2I JK LM C < `Fig.,a C N < => 2H %!./OPQR -./0 789./0! @,!S 41TUVWXC 2Y*% 27 4D%./OPQR Z[!\ ]^ { _" CMP -** #$% S 232 Arai `,***a % b 789!S NcdeQfgdh ijk-/*ῌk./* m % : `Fig..ba 0 Fig. / " 75 %z 89 789!,0ῌ,2 w w %$1< " 27 89 < %$; -* w w ]^ l 27 C ( % mn o1 Arai `,***a % CMP +1* #$%op %!S 27 % 789 qrst ABC < " qrst y 1 cdeqfgdh ijk/*ῌk+/* m 27 V C < % :C lmn S `,**.a 4D./ 2Y " Fig..b! CMP.,*ῌ+*/* #$%"& 789. /*+ ABC < *+ CMP //* #$u CMP ª«" ² ³ 2! qrst ± 1 1 µ./ 0 )D% & w @ E!S s 42 s Sato et al. L

/0 12 3 4! 5 " &9' ( Fig. /. Depth converted seismic section and geologic interpretation of the Omachi seismic section. Seismic section was projected onto an EW-trending plane. Geologic information is after Kato and Sato (+32-) and Arai (,***). Geological columnar section of a borehole by Yasaka village. Matsuta et al.,**. +32- fault-bend fold theory 0ῌ2 E (BCz {4 \ῌ]^_yῌ `abῌ cd} ~Hr E e,ῌxv k!f E " # $ %&' r g-de Fc 'h E E 7! s tvwxuῌy pvῌw7hzῌxv[y \ Suppe () * +, be \i E E]?E4BCD E E] ndebcd g o DEp ( -. +./ km jk lm '( ) * BCz zq BCr * 0ῌ ΐ ῐ Arai, Y.,,***, The late Cenozoic tectonics of the northern Fossa Magna, Master thesis. Graduate School of Science, The Univ. of Tokyo, +2,p. 34I5ῌ e,ῌ Fcῌ ksῌ ^tuῌtvw Xuv,**, w \ E x,/.p. (y a +330 /0 12 3 4 y (z ' (y a +33/ { 1 +330 { +, /*+ῌ/+*. xv kῌtv}~ +32- A 34 5 5 B C / + + ; y z 3-p. b +32- [ Z + / /+*ῌ/+.. K h +32* A E?E +/ -+ῌ.0.!4 bῌ! kῌ g ῌV^ +331 ª Y[ «C BC k E ± +*0.-,ῌ.-3. Matsuta, N., Y. Ikeda, and H. Sato,,**., The slip rate along the northern Itoigawa-Shizuoka tectonic line active fault system, central Japan, Earth Planets Space, /0, +-,/ῌ +--,. %c 5 +332 5 ª ²* U³ E E ± +*. +2.ῌ+32. 7k# +32- ~ µ $ (B /2 1++ῌ1,,. ῌ% ῌ74kQῌIV ¹ +33+ /0 GPS»¼ 12 ºEy. /0 12 3 4! 5 # / 3 4 " 2 6#78 $ % 0.. km " &9' ( 6: ;) * < ( + km + 2 %#= * >? )* + km " @ A(%+ 8 * ῒ ῑ * BC, DE-DEBC. F/ 0G ++.2**+3 BC12Hῌ34I5 * &9' (!J 6K7 L!J M N6K7 O# P8Q 9R :S6; ' T' * AA U) VW<)+#*!&9' ( XYZ[ =>H : 34I5 \ E E]?E4BCD ^_`@=>H : 9AB \ E E]?E4BCD XYZ[2CaD : 34I5ῌ 9ABῌ4EFbῌ& cide \ E E]?E4BCD 4 fgῌg *HhῌIJ?iῌK jkῌ&jlmῌn4lmῌo npqῌo4pqῌrstu \ E?E?Er 43

00,2/,32.,***.0 +11 +20. Okumura, K.,,**+, Paleoseismology of the Itoigawa-Shizuoka tectonic line in central Japan, Jour. Seismol., /,.++.-+.,**0,0 +,+ +-0. +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. +33/ + : +**,*** Suppe, J., +32-, Geometry and kinematics of fault bend folding, American Journal of Science,,2-, 0.2 1,+. +333 + :,/,*** D. +-No. -02.,***,, 033 1*/. +323,* + Received March 1,,**1 Accepted June,3,,**1 44