Shallow seismic reflection profiling across the western marginal faults of Kitakami Lowland, northern Honshu Island, Japan

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1 Bull. Earthq. Res. Inst. Univ. Tokyo Vol. 2+,**0 pp * +,, - +. / 0 1 +, -. : / 0 1 Shallow seismic reflection profiling across the western marginal faults of Kitakami Lowland, northern Honshu Island, Japan Eiji Kurashimo + *, Hiroshi Sato +, Shin Koshiya,, Masaru Noda,, Hazime Kato -, Sumiko Ogino +, Tetsuya Takeda., Shin-ichi Hirano /, Yasutaka Ikeda 0 and Takeshi Ikawa 1 + Earthquake research institute, the University of Tokyo,, Faculty of Engineering, Iwate University, - Faculty of Education and Human Sciences, University of Yamanashi,. Earthquake research institute, the University of Tokyo (Present, National Research Institute for Earth Science and Disaster Prevention), / Faculty of Science, Tohoku University, 0 School of Science, the University of Tokyo, 1 Japex Geoscience Institute Inc. Abstract In , integrated passive and active seismic experiments were conducted in northern Honshu, Japan. These experiments aimed at understanding the relationship between earthquake occurrence and deformation process of the intra-island-arc crust. In the summer of +332, a shallow seismic reflection survey was conducted to obtain the fault s detailed geometry to depths of + km across the western marginal faults of Kitakami Lowland, Iwate Pref., Japan. The seismic source was a mini-vibrator. The data set recorded by the digital telemetry system was processed using seismic reflection technique. Imaging was preformed using conventional common mid-point processing steps, including post-stack migration and depth conversion. A reflection image shows the deep geometry of the Uwandaira fault, which is positioned at the eastern edge of the Ou Backbone range. Key words: shallow seismic reflection profiling, reverse fault, western marginal faults of Kitakami Lowland, northern Honshu , Iwasaki et al.,,**+, Sato et al.,,**,, Matsubara et al.,,**. Sato et al.,,**, / km Sato et al.,,**, +33+ * ekura@eri.u-tokyo.ac.jp ++- **-,

2 ¹ º» Fig. +. Map showing the location of the shallow seismic reflection survey line and stacking line. Base maps are parts of + :,/*** topographic map Shiwa, Hizume, Hanamakionsen and Ishidoriya of Geographical Survey Institute. tusva lwe! - km ῌ +33+ ῌ )45HI x y"x Fig. + z{!" #$%& ' ( )* 0}#~$ +* Hz 3 J ) +c X +,-#./ )45 HIJ +,./ m. ) O Q ` P^_à% ; < =>+ ( k ῌ +33+ GDAPS-. +c X. &0 +-* A./ 0 B 78? CDE" ch 0 /** Hz K P^ 9+F G ( A? B & 0 - sec X. )*0' Industrial Vehicles X. z{ 0,.* 3 ) )45 H International IVI ( PQP)* b IJ K L. Figs. + and, M 0 B c X _ P ~$ 0 +*ῌ2* Hz I )45 N OPQ R ST U V# _ P _ P 0 +/ ) )+KL. ) 0,/ m + / y +KL.,ῌ ῑῒ ῐ ) 0 &+ ª B 3 )450W X YZE )[\] ^_à b c X d,. 2 d,2 ( e fgx. 45 OPQh =# i + Table + j# HI0klmnopqZrs( X.«* +,+ Fig. - j# Fig. - 0J ± # z{.² RP.+ ) ³ %. 0 X.z{ µ H / 3$ : ; ¼ 140 ¼

$/, Refraction Analysis, Fig. 0 iras + *./ km/s - First Break Mute.$

3 Fig.,. Geological map around the study area. Table +. Data acquisition parameters for the present seismic reflection survey. - Fig.. Mercury International Technology MIT ixl + Geometry Set. Fig. + CMP 0.,/ m /* Fig. /, Refraction Analysis, Fig. 0 iras + *./ km/s - First Break Mute. Bandpass filter Low Cut: / Hz, Low Pass: +* Hz, High Pass: 2* Hz, High Cut: 2/ Hz / Gain Recovery Automatic Gain Control; AGC AGC,** ms 0 Deconvolution 141

4 Fig. -. Example of the observed seismograms. Location of shot point is RP.+. The horizontal axis represents the source-receiver o#set. A band-pass filter of / 2/ Hz and a,** ms automatic gain control are applied. Fig... Flow chart of data-processing. Filter : +/** ms : +/* ms :. ms : - 1 Static Correction 2 NMO Normal Move-out Correection Velocity Analysis Fig. 1 NMO CMP.*, 3*, +-*, +1*,,**,,-*,,0*, -**, -.*,.** 3 Residual Static Correction, ms NMO CMP +* CMP Stack Fig. 1 NMO CMP ++ Migration 142

5 Fig. /. Distribution of number of folds along the 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 first layer. 143

Fig. 1. Stacking velocities determined by velocity analysis. Velocities are shown using a gray scale. Solid counter lines indicate velocity in km/s. The counter interval is *., km/s.

6 Fig. 1. Stacking velocities determined by velocity analysis. Velocities are shown using a gray scale. Solid counter lines indicate velocity in km/s. The counter interval is *., km/s. Numerals indicate P-wave velocity in km/s. NMO +, Depth Conversion. Fig.. Fig 2 Fig. 3 Fig. 3 RP 1* *.1 km Fig. 3 *.. km RP +-RP 1* *.2 km + km RP 1*-+-* RP +0* *.- km RP +0* Fig., RP 1* RP 2* RP +/* *.- *.1 km.* Fig., / km *.1 km 144

7 Fig. 2. Unmigrated stacked time section. 145

8 Fig. 3. Post-stack migrated depth section. ῐ ῑ ῌ 146 ῌ

9 Iwasaki, T., W. Kato, T. Moriya, A. Hasemi, N. Umino, T. Okada, K. Miyashita, T. Mizogami, T. Takeda, S. Sekine, T. Matsushima, K. Tashiro and H. Miyamachi,,**+, Extensional structure on northern Honshu Arc as infeered from seismic refraction/wide-angle reflection profiling, Geophys. Res. Lett.,,2, +,,,-,3,--, ,-,,.* +33+,.-1pp. Matsubara, M., N. Hirata, H. Sato and S. Sakai,,**., Lower crustal fluid distribution in the northeastern Japan arc revealed by high-resolution -D seismic tomography, Tectonophysics, -22, --./ / +** +*/ Sato, H., N. Hirata, T. Iwasaki, M. Matsubara, and T. Ikawa,,**,, Deep seismic reflection profiling across the Ou Backbone range, northern Honshu Island, Japan, Tectonophysics, -//,.+ /, ,/ Received November +.,,**0 Accepted January +3,,**1 147

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