High-Resolution P-wave Seismic Reflection Imaging of the Suzuka Basement-Involved Fold:,**/ Tokiyama Profile

Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2,,**1 pp. 3/ +*- P :,**/ + *, -. / 0 1 2 3 +* ++ +, +- +. + :, -. : / : 0 : 1 2 3 : +* ++ +, : +- : +. : High-Resolution P-wave Seismic Reflection Imaging of the Suzuka Basement-Involved Fold:,**/ Tokiyama Profile Tatsuya Ishiyama + *, Hiroshi Sato,, Shigeru Toda -, Nobuhiko Sugito., Haruo Kimura /, Tomoo Echigo 0, Shinsuke Okada 1, Hajime Kato 2, Atsumasa Okada 3, Taro Koike +*, Norimasa Suzuki ++, Tomohiro Imamura +,, Yasuhisa Hattori +- and Shin Oda +. + Active Fault Research Center, National Institute of Advanced Industrial Science and Technology (Present Address: Graduate School of Science, Tohoku University),, Earthquake Research Institute, the University of Tokyo, - Aichi University of Education,. Graduate School of Science, Kyoto University (Present Address: Research Center for Seismology, Volcanology and Disaster Mitigation, Graduate School of Environmental Studies, Nagoya University), / Earthquake Research Institute, the University of Tokyo (Present Address: Institute of Geology and Geoinformation, National Institute of Advanced Industrial Science and Technology), 0 Graduate School of Science, the University of Tokyo (Present Address: Geo-Research Institute), 1 Graduate School of Science, the University of Tokyo, 2 Faculty of Education and Human Sciences, Yamanashi University, 3 Graduate School of Science, Kyoto University (Present Address: Research Center for Disaster Mitigation of Urban Cultural Heritage, Ritsumeikan University), +* Geosys, Inc., ++ Aichi University of Education (Present Address: Toyota Municipal Wakazono Junior High School), +, Graduate School of Science, Kyoto University (Present Address: Tango Civil Engineering O$ce, Kyoto Prefecture), +- Graduate School of Science, Kyoto University (Present Address: Japan Energy Co., Ltd.), +. Graduate School of Science, the University of Tokyo (Present Address: Idemitsu Kosan Co., Ltd.) Abstract We present new, high-resolution seismic reflection data (,**/ Tokiyama profile) acquired across the piggyback basin between the Yoro and Suzuka basement-involved folds to further image its subsurface geometry. A seismic source (mini-vibrator) and +2*-channel digital telemetry recording system were used in an split-spread configuration with the nearest receiver adjacent to the source to record seismic waves from deeper reflection points. A +*-m source and geophone spacing give a /-m CMP (common midpoint) spacing on the final section. The nominal CMP stacking fold had 3* * e-mail: t-ishiyama@mail.tains.tohoku.ac.je 32* 2/12 0-95

traces. We also suppressed coherent noise by repeating source points 1 +* times. After data processing including surface-consistent statics, velocity analysis, normal moveout (NMO) correction, residual statics, CMP stack, and migration, the section was finally depth-converted using stacking velocities. Reflectors imaged on the seismic profile Illuminate that the forelimb composed of Pliocene-Pleistocene Tokai Group and underlying Mesozoic basement rocks are thrust over intermontane units. The uniform thickness of the Tokai Group on the west flank of the Yoro Mountains also indicates its pregrowth nature to the Yoro basement-involved fold. Key words: active fault, Suzuka basement-involved fold, Yoro basement-involved fold, seismic reflection profile, central Japan + Ishiyama et al.,,**. ++* km +33+;,**,;,**, ; Fig. + basement-involved fold,**1 P Ishiyama et al.,**1, P,**/, +,**/,**/ /.* km Fig., +32.; +33+;,**, +322,**, +322 Fig.,,**/, +2,1 +* -0/ m,, Table + +, km GDaps-. T- +/*** IVI +330 +2* +* Hz 3 +* m +/ sec, +* +,* Hz 1 3* 96

,**/ $ i ῌ VO Fig. +. (a) Shaded relief map based on,/* m digital elevation model (DEM) (Kishimoto et al.,,***) showing the topography and distribution of active faults within the Kinki region, central Japan. Locations of active faults are from Nakata and Imaizumi (,**,). Red, orange, and gray lines mark active faults that are precisely located, approximately located, and inferred, respectively. Barbs denote hangingwalls of active thrusts. Arrows indicate slip directions of strike-slip faults. Abbreviations for metropolitan areas are : KB : Kobe, OK : Osaka, KT : Kyoto, NG : Nagoya. (b) Regional geologic map of the Nobi-Ise fault zone (modified from Ishiyama et al.,,**1). Geologic units are modified from Miyamura et al. (+310), Takada et al. (+313), Yoshida (+32. ; +322), Harayama et al. (+323), and Yoshida et al. (+33+). Red line with solid circles indicates location of the seismic line in this study. ῌ O 7# 0* ch, b7# +,* ch cdegfg&hi! "# 2j/ klmnkopqr&fg2vo5% stb $%& '()! " *+,-./0 uuvvb VO5%&awxyz{2 +* 1 234 567 89:;#<67 }B,hi~ 2j B #, - [\ =>ῌ?>@ A5B,/ 01#CD 0 a +,,** m & ῌhi a\l m EFGH% IJK 2LM NO2EPQRST lyzo2 / NV EP B +322 U VOWX% +2* YZ[\2].^_` av 97 a G N!2ST,/

¹º» Fig.,. Detailed topographic map showing locations of survey line with receiver points and stack line with CMP (common midpoint) numbers. Locations of active fold scarps along the Yoro fault is modified from Ikeda et al. (,**,). Fig. - ++-/ *+ #X 2W w ab x y 5X #z +,*- {NT } 5 X #e~\ \ Fig. +,/-!"#$%&'()*+ + sec, -./ 0 12 3. X #y \] Table, () ῌ # 8 *+ + sec, 4-5'6$%&./ 78' ῌ # qr0<=# 0 9 :;#$%& <=>3;#? @ 8k 7A ZTklmn ῌop" /@6A,B CDEF GBH- 5IJKL ab3 op<= ab Fig.,,B op MNO 78' 0 <= qrntklmn # a # \ 0 CMP YZB -ῌ ῐῑ ῌe ]\ PQR SB*+ NT $% UV t &5 # & ª«&# B@#$%WX YZB [\]^_ `at b B@ ῌe ]\ ab c$%w[\]x de fgh ProMAXTM Land- ab # \± &" ² a ³ mark ij # µ at ab NB $%W#X klmn op W qr0 Yilmaz +321 stua lv#$%& ¼ 98 ¼

,**/ Table +. Recording parameters for the,**/ Tokiyama seismic reflection profile. CMP + Fig. / a final datum Fig. / b +,,*** m sec + NMO CMP +** CMP,/ Fig. 0 NMO CMP NMO Fig. -. Shot gathers obtained at shot points ++-/, +,*-, and+,/-. 99

Table,. Processing parameters for the,**/ Tokiyama seismic reflection profile. Fig... Flowchart of data processing. NMO Fig. 0 NMO CMP S N Fig. 1 a F-X Fig. 1 b Fig. 1 a Fig. 2. + km 100

,**/ Fig. /. (a) Near-surface velocity structure based on refraction statics calculation. Dark and light gray lines indicate velocity of the bottoms of weathered and underlying layer, respectively. (b) Receiver (open squares) and source (solid circles) statics to final datum based on refraction statics calculation. Fig. 0. Stacking RMS velocity structure based on velocity analysis. Fig. 2 101

ῐῑ Fig. 1. Fig. 2. (a) Filtered stack section and (b) migrated time section based on data processing. Depth, migrated section based on data processing (Modified from Ishiyama et al.,,**1). ῌ 102 ῌ

,**/ Yoro basement-involved fold pregrowth strata Ishiyama et al.,,**1 /,**/, +2,,1 /.* km Yoro basement-involved fold pregrowth strata +0 +1 A +0,***/* : +323 / + +./ p.,**,,/. p. Ishiyama, T., K. Mueller, H. Sato, and M. Togo,,**1, Coseismic fault-related fold model, growth structure, and the historic multisegment blind thrust earthquake on the basement-involved Yoro thrust, central Japan, J. Geophys. Res., doi: +*.+*,3/,**0JB**.-11.,**1 P :,**. 2, 0/ 1.. +33+.-1 p.,*** : Japan,/*m.grd, CD- ROM -/- + CD-ROM, +310 / +.3 p.,**, 0* p. +32. /1 Ser. A,-1,0,. +330 +/ +** +*/. +313 / + /0 p. Yilmaz, O., +321, Seismic Data Processing, Soc. Exploration Geophys., Tulsa, Oklahoma, /,0 p. +32. / + 2+ p. +322., + +0. +33+ / + +/. p. Received March,-,,**1 Accepted May 3,,**1 103