日本地球惑星科学連合2019年大会

講演情報

[J] ポスター発表

セッション記号 S (固体地球科学) » S-SS 地震学

[S-SS13] 強震動・地震災害

2019年5月27日(月) 15:30 〜 17:00 ポスター会場 (幕張メッセ国際展示場 8ホール)

コンビーナ:栗山 雅之(一般財団法人 電力中央研究所 地球工学研究所 地震工学領域)、染井 一寛(一般財団法人地域地盤環境研究所)

[SSS13-P05] Exploration of the velocity structure model in the Mukawa town, damaged area during the 2018 Hokkaido eastern Iburi earthquake

*重藤 迪子1高井 伸雄2堀田 淳3野本 真吾 3前田 宜浩4高橋 浩晃2一柳 昌義2山中 浩明5地元 孝輔5津野 靖士6是永 将宏6山田 伸之7 (1.九州大学、2.北海道大学、3.株式会社ジオテック、4.防災科学技術研究所、5.東京工業大学、6.公益財団法人鉄道総合技術研究所、7.高知大学)

キーワード:2018北海道胆振東部地震、速度構造モデル、微動観測、表面波探査

The 2018 Hokkaido eastern Iburi earthquake (Mw 6.6, focal depth=37 km) occurred on 6 September 2018 at the Hidaka arc-arc collision zone, Hokkaido, Japan. The many building damages by strong ground motion were concentrated around K-NET Mukawa strong motion observation station (HKD126). Strong motion records had strong power in 1-2 second periods of the response spectrum to destroy the timber frame buildings. It is an important examination to know the cause of the generation of this destructive strong motion.

To understand the site effects of this strong motion, we estimate the velocity structure models by using the microtremor array and multichannel analysis of surface wave measurements at three sites; around HKD126 site, a hillside site located about 6 km north from HKD126, and midpoint between both sites. We carried out the microtremor array measurements (R=1-2000 m) on 14-16 December 2018. We used servo type velocity sensor (Le-3D/5s) and 24-bit data logger (DATAMARK LS-7000XT) with GPS time calibration. At small arrays (R<~10 m), we used moving coil accelerometer (JEP-6A3, 10V/g). The fundamental Rayleigh wave phase velocity is examined with the spatial autocorrelation method. We also carried out a multichannel analysis of surface wave to emphasize the high-frequency side phase velocity. We set 24 channel 4.5 Hz geophones in interval 1 m with GEODE and 10 kg wood hammer. The phase velocity is examined with the Frequency-wavenumber method. The shear wave velocity structure models are estimated to fit the dispersion curve of the fundamental mode of Rayleigh wave using the genetic algorithm inversion method (Yamanaka and Ishida, 1998). The phase velocity data of the large array (R=2000 m) were used in common to the three sites.

Comparing the velocity structures, the Vs=1300 m/s layer’s depth of HKD126 is shallower than the hillside site ones and midpoint depth is mid of both. This tendency of depth variation is the same as the seismic bedrock and subsurface structure depth variation of AIST model (Yoshida et al., 2007) and J-SHIS V2 model (Fujiwara et al., 2012). On the other hand, about the shallow part, engineering bedrock depth of hillside site is shallower than the HKD126. The midpoint’s seismic bedrock is mid for the others, however, the surface soft soil deposit is detected as richer than the HKD126. These features of the shallow part structure's variation are able to confirm by the surface geology or Vs30 values of J-SHIS.

Acknowledgements: A part of this study was supported by the Grant-in-Aid for Scientific Research No. 18K19952 and 17H06215 from MEXT of Japan, and MEXT of Japan’s Earthquake and Volcano Hazards Observation and Research Program.