Estimation of S-Wave Velocity Profiles and Site Amplification Around the K-NET Tsukidate Station, Miyagi Prefecture, with Reference to Large PGA During the 2011 off Pacific Coast of Tohoku Earthquake, Japan
Hiroaki Yamanaka*1, Kosuke Chimoto*1, Seiji Tsuno*2,
Yadab. P. Dhakal*1, Mohamed Amrouche*1, Nobuyuki Yamada*3,
Shun’ichi Fukumoto*4, and Kiminobu Eto*4
*1Department of Environmental Science and Technology, Tokyo Institute of Technology, 4259 Nagatsuta, Midori-ku, Yokohama, Kanagawa 226-8502, Japan
*2Railway Technical Research Institute, 2-8-38 Hikari-cho, Kokubunji-shi, Tokyo 185-8540, Japan
*3Fukuoka University of Education, 1-1 Akamabunkyomachi, Munakata City, Fukuoka 811-4192, Japan
*4Tokyo Soil Research Co., Ltd., 2-11-16 Higashigaoka, Meguro-ku, Tokyo 152-0021, Japan
In this study we investigated site amplifications in shallow soil around Tsukidate station (MYG004) of KNET in Miyagi prefecture with a seismic intensity of 7 during the 2011 off the Pacific Coast of Tohoku Earthquake from aftershock observation and microtremor explorations. We conducted aftershock observations by installing 8 temporary stations. We estimated site amplifications of S-wave from the observed data. We found that the predominant period of amplification at a site near MYG004 was 0.2 seconds. The amplification factor at a site on cut ground with a distance of 20 m from MYG004 was significantly different. Furthermore, the amplifications were also different with changing predominant periods from 0.1 to 0.5 seconds in an area of 1 km from MYG004. Shallow Swave velocity profiles were deduced from microtremor array explorations at the stations. Results indicated that shallow low-velocity layers with a thickness of less than 30 meters are responsible for variation of the amplifications. Predominant periods in calculated 1D amplifications were similar to those observed in the aftershock observations. The observed amplification factor at the site nearMYG004, however, was two times larger than the calculated one, suggesting the inappropriateness of the 1D assumption at the site possibly due to the effects of a cliff near MYG004. We also found from horizontal-vertical ratios of microtremors that the site effects on the cliff were also different at frequency higher than 10 Hz within 30 meters around MYG004. This also suggests lateral variation in the site effects at the high frequency near MYG004.
-  S. Midorikawa and H. Miura, “K-NET Tsukidate Strong Motion Record and Nearby Damage during the 2011 off the Pacific Coast of Tohoku Earthquake,” Summary of Technical papers of Annual meeting of AIJ, B-2, pp. 37-38, 2011 (in Japanese).
-  H. Iizuka, Y. Hayashi, Y. Sakai, and K. Kanda, “Ground Motion and Building Damage during the 2011 off the Pacific Coast of Tohoku Earthquake, Part 1 Earthquake records and damage near strong motion site” Proceeding of the 8th Annual Meeting of Japan Association for Earthquake Engineering, pp. 40-41, 2011 (in Japanese).
-  M. Motosaka and T. Tsamba, “Investigation of high acceleration records at K-NET Tsukidate station during the 2011 off the Pacific coast Tohoku Earthquake,” Proceeding of the 8th Annual Meeting of Japan Association for Earthquake Engineering, pp. 24-25, 2011 (in Japanese).
-  S. Matsushima, F. Nagashima, H. Kawase, T. Hayakawa, M. Oshima, T. Satoh, Baoyintu, and K. Nakano, “Aftershock observation of the 2011 off the Pacific Coast of Tohoku earthquake near K-NET Tsukidate,” Proceeding of the 8th Annual Meeting of Japan Association for Earthquake Engineering, pp. 446-447, 2011 (in Japanese).
-  H. Yamanaka, S. Tsuno, K. Chimoto, N. Yamada, S. Fukumoto, and K. Eto, “Estimation of site amplification from observation of aftershocks of the 2011 off the Pacific Coast of Tohoku earthquake and microtremor explorations in the vicinity of K-NET Tsukidate station, Miyagi prefecture, Japan,” Geophysical Exploration (Butsuri Tansa), Vol.64, pp. 389-399, 2011 (in Japanese).
-  T. Hayakawa, M. Oshima, T. Satoh, H. Kawase, S. Matsushima, Baoyintu, F. Nagashima, and K. Nakano, “Estimation of surface layer at K-NET Tsukidate using microtremor array observation and site effects,” Proceeding of the 8th AnnualMeeting of Japan Association for Earthquake Engineering, pp. 444-445, 2011 (in Japanese).
-  Y. Sakai, A. Aoi, K. Arai, and T. Suzuki, “Damage Investigation of Surroundings of the Seismic Stations in the 2008 Iwate-Miyagi Nairiku Earthquake and Correspondence of Damage to Bulidings with Strong Ground Motions,” Journal of Japan Earthquake Engineering Association, Vol.10, No.4, pp. 14-53, 2010 (in Japanese).
-  H. Yamanaka, “Inversion of surface-wave phase velocity using hybrid heuristic search method,” Geophysical exploration (Butsuri Tnasa), Vol.60, pp. 265-275, 2007 (in Japanese).
-  H. Yamanaka, M. Takemura, H. Ishida, and M. Niwa, “Characteristics of long-period microtremors and their applicability for exploration of deep sedimentary layers,” Bull. Seism. Soc. Am, Vol.84, pp. 1831-1841, 1994.
-  H. Arai and K. Tokimatsu, “S-Wave Velocity Profiling by Inversion of Microtremor H/V Spectrum,” Bull. Seism. Soc. Am., Vol.94, pp. 53-63, 2004.
-  National Research Institute for Earth Science and Disaster Prevention, Japan Seismic Hazard Information Station (J-SHIS),
http://www.j-shis.bosai.go.jp/ [accessed Aug. 10, 2012]
This article is published under a Creative Commons Attribution-NoDerivatives 4.0 Internationa License.