Department of Earth & Planetary Science, the University of Tokyo, - Department of Geology Earth material science, Niigata University,

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1 Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2*,**/ pp. + 3,**. : + * +, + -. / , 2 +* +* +* +, -. / * High-resolution seismic reflection profiling across the surface rupture associated with the,**. Mid-Niigata Prefecture earthquake, central Japan: data acquisition and processing Hiroshi Sato + *, Naoko Kato +, Tomo-o Echigo,, Sumiko Ogino +, Masaaki Tateishi -, Shigeru Toda., Hajime Kato /, Shin Koshiya 0, Tsuyoshi Toyoshima -, Tanio Ito 1, Toshifumi Imaizumi 2,Shitaro Abe 3, Norimasa Suzuki.,Eiichi Misawa 1,Shin Oda,,Kyoko Kagohara 2, Taro Koike +*, Satoshi Akai +*, Katsuya Noda +* + Earthquake Research Institute, the University of Tokyo,, Department of Earth & Planetary Science, the University of Tokyo, - Department of Geology Earth material science, Niigata University,. Aichi University of Education, / Faculty of Education and Human Sciences, Yamanashi University, 0 Department of civil & Environmental Engineering, Iwate University, 1 Department of Earth Sciences, Chiba University, 2 Department of GeoEnvironmental Science, Tohoku University, 3 Central Research Institute of Electric Power Industry, +* Geosys, Inc. Abstract The,**. Mid-Niigata Prefecture earthquake (Mj 0.2) generated surface ruptures along the eastern rim of the Uonuma hills. To reveal the relationship between a seismogenic source fault and surface ruptures, shallow, high-resolution seismic reflection profiling was undertaken across the surface ruptures and the active faults. The seismic source was a mini-vibrator and seismic data were recorded by a digital telemetry system. The source and receiver interval was +* m. The seismic data were processed using conventional CMP seismic reflection methods. The resultant depth-converted seismic section portrays an emergent thrust beneath the surface rupture associated with the Mid-Niigata Prefecture earthquake. Key words:,**. Mid-Niigata Prefecture earthquake, surface rupture, subsurface structure, seismic reflection profiling, active fault-and-fold, central Japan +,**. +*,- +1 / * satow@eri.u-tokyo.ac.jp ++- **-,

2 ¹K º» Fig. +. Geological map showing the seismic line Hirokami,**.. Major geologic structure is after Yanagisawa et al. (+320). Pre-N : mainly pre-neogene rocks with minor distribution of lower Miocene andesite. Figures in Italic are numbers of receiver points. + M 0.* s? /t ujk;,**. M 0./ 0 vwxyz{ OHI }~ $! "#$%& +* ',- U HI p "H ( M /.1 ) 0 *+ +* ',1 ( M 0.+ ) Iῌ" l V /$ 0 *+ ++ ' 2 ( $ M /.3 ) / +, -.-& / 0!! = 78 h, '! k ;,**. v +, 'm :;< j :; m j 12 J$ = : D $ j hg BC V / L; EFG HIJ $ KLMMN H V /$ Kato et al. OHI : / 3 / ; ) PQ,**/ ; ),**/+ 3 Hirata et al.,,**/+ R ST U HI V /$ WXYZ [\ H&] ^ / ;,ῌ ῐ _`abcd789ῌ"hi78efgh ijj $ w 3 / ; )Maruyama et al.,,**/+ "HIk; I r;wx 4 ª«r pqr;hi "# : ; $ 6] $(.-& /, :T $ / + 1 v±² ³3 µ Jk z $" l mno ¼ 2 ¼

,**. 0,*** m,***; +33, +320 Figure + Maruyama et al.,**/.** m,**+ +32/ +320 /**,,*** m,*** +320 + Ma Fig.,. A mini-vibrator truck (IVI, T-+/***) used in the seismicprofiling.,**+;,**. -,**.

3 ,**. 0,*** m,***; +33, +320 Figure + Maruyama et al.,**/.** m,**+ +32/ +320 /**,,*** m,*** Ma Fig.,. A mini-vibrator truck (IVI, T-+/***) used in the seismicprofiling.,**+;,**. -,**. - + WNW-ESE /., km Fig. + RP.*+..1 Fig. + Table + IVI T+/***; +330 Fig., JGI G-daps., msec, +2* +* m +* Hz - +* m +* +** Hz,* / 1 +* 0* +,*,**. +, +3,1 Fig. - +* 2* Hz, +* +** Hz, +* +,* Hz - +2* 0** msec AGC +**,** ms 2* Hz +** Hz +** Hz +,* Hz 3

4 Table +. Data acquisition parameters for the Hirokami,**. seismic line. +,* Hz +** Hz +* +** Hz -, Fig.. Table, Super X Geometry Set Fold Stacking Line Fig. + CMP 30 Fig. / Automatic Gain Control; AGC AGC operator length: +** msec Deconvolution Operator length:,** msec Gate length:,*** ms White noise: / Prediction length: 2 ms Static Correction Time-Term Fig. 0 iras P 2** m sec Fig. 0 RP.**, km sec,./ km sec 4

5 ,**. Fig. -. Examples of shot gathers at di#erent sweep frequency. A. Sweep frequency +* 2* Hz. B. Sweep frequency +* +** Hz C. Sweep frequency +* +,* Hz. Super X NMO Normal Move-out Correction Velocity Analysis NMO CMP NMO NMO CMP/* Fig. 1 Residual Static Correction, ms CMP Stack NMO CMP Bandpass Filter : +*,* +** ++* Hz F-X F-X Prediction Filter Gate length: -* traces Operator length: / traces window length: +,*** ms Migration Percent velocity scale factor: +** Depth Conversion Fig. 2 Fig. 3. Fig. 3 CMP//* * /** m,./ -.* km sec RMS 5

6 Fig... Flow chart of data-processing. Table,. Processing parameters for CMP Hirokami,**. seismic data. 6

7 ,**. Fig. /. Distribution of number of folds along a CMP stacking line. Fig. 0. Surface structure determined by time-term analysis. (a) time-terms, (b) velocities of second layer, (c) topography and geometry of surface low velocity layer. CMP1** CMP-** /** m CMP1** -* Fig. 3 -* CMP,**.** +320 Fig. 3 Maruyama et al.,**/ Fig. 3,**+ 7

$% " ( AB&CDEF GH%I JKDELMNF O PQ O 0 RST 1** /ῌ m UVWX 'YZ T[\]'^_ Z `ab!$

8 qrstu v Fig. 1. Fig. 2. Optimum stacking velocities determined by velocity analysis. Filtered stacked section (A) and post stacked, migrated time section (B). >?@?% " ( AB&CDEF GH%I JKDELMNF O PQ O 0 RST 1** /ῌ m UVWX 'YZ T[\]'^_ Z `ab! " #$%&'( )* +,-./ ( 0 )X cdef ]g` ) hi X0 'YZjkl mn op]'^_ Z /., km 7) 0 9:;<= w 8 w

$/0 H% I3D+ JKL MN ;" = OP & JKLQRSTU' V WX1YZ 5 ( B)[ WX YZ+ * \]^_)`+a` b 5 #B+ N J,**..L qn cdef,g- ῌ hi j k +0.$

9 ,**.. l m nῌ n<»ª«g¼, n#b Fig. 3. Depth converted seismic section.! " # $% & '% ( ) * +, -./ :;"< = ; > + #B $CD1EFῌ #BG-./0 H% I3D+ JKL MN ;" = OP & JKLQRSTU' V WX1YZ 5 ( B)[ WX YZ+ * \]^_)`+a` b 5 #B+ N J,**..L qn cdef,g- ῌ hi j k +0. l m n o^_hi p J/0 : 1 cd = rst%l GuvwCDxyz{ 5 }CD~ 0^5 ῌ 2 ῌ 34 ῌ 5 n =hi6n 7 l m n 8w6n9.,**/,**.. 1/ +.3ῌ+/+5 :WX ;z{_n < N Hirata, N., H. Sato, S. Sakai, A. Kato, E. Kurashimo,,**/, Fault system of the,**. Mid-Niigata Prefecture Earthquake and its aftershocks, Landslides,,, +/-ῌ+/1. Kato N., T. Echigo, H. Sato, M. Tateishi, S. Sakai, S. Ogino, S. ' Toda, S. Koshiya, T. Ito, T. Toyoshima, T. Imaizumi, H. Kato, S. Abe,,**/, High resolution seismic reflection profiling across the surface rupture associated with the,**. Mid-Niigata Prefecture earthquake (M 0.2), central Japan, Earth Planet. Space, /1,..1ῌ./,. =,**. 67 >G=?w@AB< G CD <,. 0-ῌ1/. Maruyama, T., Y. Fusejima, T. Yoshioka, Y. Awata and T. Matsu ura,,**/, Characteristics of the surface rupture associated with the,**. Mid Niigata Prefecture earthquake, central Japan and their seismotectonic implications, Earth Planet. Space, /1, /,+ῌ/,0. l \E,*** l F J,***.GL l,** p n = HIz{, n#bst < +/ +**ῌ+*/. T ῌ JK L M2 +33, j\ega G Lῌ T p5 /,* p. Nῌ&O % +32/ 67 ) ªP «G Q R ;" j)msῌtusp V no.,, p..+ῌ./. WXY*ῌZ ῌ[ ±ῌ =ῌ ²\,**+ + :,/ *** ]8³ < j ( p5 ^ µcd _ D. +-No à bῌ cdῌef ῌg ¹ῌºsuhῌ i u +320 ( «G 5 «V J/ j9g + kl,b= +11 p. JReceived February,,,,**/L JAccepted August +0,,**/L 9

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