Japan Geoscience Union Meeting 2018

Presentation information

[JJ] Evening Poster

H (Human Geosciences) » H-TT Technology & Techniques

[H-TT19] New Developments in Shallow Geophysics

Thu. May 24, 2018 5:15 PM - 6:30 PM Poster Hall (International Exhibition Hall7, Makuhari Messe)

convener:Kyosuke Onishi(Public Works Research Institute), Kunio Aoike(Oyo corporation), Keisuke Inoue(国立研究開発法人 農業・食品産業技術総合研究機構, 共同), Tishiyuki Yokota(National Institute of Advanced Industrial Science and Technology)

[HTT19-P06] Very shallow S-wave seismic reflection survey across the surface rupture of 2014 Naganoken-hokubu earthquake, central Japan

*Shinsuke Okada1, Takahashi Naoya2, Kazuo Yamaguchi3, Tatsuya Sumita3, Yuichi Niwa4, Keitaro Komura5, Haruo Kimura5 (1.International Research Institute of Disaster Science, Tohoku University, 2.Graduate School of Science, Tohoku University, 3.National Institute of Advanced Industrial Science and Technology, 4.Faculty of Science and Engineering, Chuo University, 5.Central Research Institute of Electric Power Industry)

Keywords:very shallow S-wave seismic reflection survey, 2014 Nagano-ken-hokubu earthquake, Kamishiro fault, Itoigawa-Shizuoka tectonic line active fault zone

The Nagano-ken-hokubu earthquake (Mw 6.2) occurred on 22 November 2014. Along the pre-existing trace of the Kamishiro fault, a 9.2-km-long surface rupture emerged from Shiojima in Hakuba village of Nagano prefecture to Higashi-sano. In the northern part of the surface rupture zone, east-dipping reverse faults were identified as a master fault considered from distribution of surface rupture, amount of the vertical/horizontal displacement, ground deformation, morphological style, and deformation of artificial structure. On the other hand, buckled steel handrail and drainage gutter were observed in the southern part of the surface rupture zone, which suggest the low angle fault at shallow depth. Also, low angle trust fault observed in the trenching survey (Okumura et al., 1998, J Seismol. Soc. Japan 2nd ser. Zisin, 50, 35-51).

In this survey, to reveal the subsurface structure of the northern part of the surface rupture, we conducted very shallow S-wave seismic reflection survey from November 21 to 23, 2016 at Oide in Hakuba village, Nagano prefecture. The length of seismic reflection survey line was 300 m from west to east across the 2014 surface rupture. To generate SH-waves in a direction perpendicular to seismic line, we hit a sidewall of square wooden log (0.2 x 0.4 x 1.0 m, 28 kg, pine wood) with a sledgehammer as a source in this survey. The receiver was GS-32CT (natual frequency, 10 Hz), and sampling rate is 1 ms during 2 sec of recording time. The source and receiver spacing was 1 m with 96 ch geophones used for each recording. We selected the DSS-12 (Suncoh consultants co. ltd.) for the recording system. In this presentation, we demonstrate the very shallow S-wave seimic reflection survey across the 2014 surface rupture along the Kamishiro fault in Oide of Hakuba village, Nagano prefecture.

This survey was supported by a special grant of the Ensemble Project for Young Researchers, Tohoku University. We thank land owner, local people, and village office for their support during our survey.