2018 Fiscal Year Final Research Report

Development of a microtremor exploration method using miniature arrays

Research Project

PDF

Project/Area Number	17K18962
Research Category	Grant-in-Aid for Challenging Research (Exploratory)
Allocation Type	Multi-year Fund
Research Field	Social systems engineering, Safety engineering, Disaster prevention engineering, and related fields
Research Institution	National Institute of Advanced Industrial Science and Technology
Principal Investigator	Cho Ikuo 国立研究開発法人産業技術総合研究所, 地質調査総合センター, 主任研究員 (10328560)
Co-Investigator(Kenkyū-buntansha)	横田俊之国立研究開発法人産業技術総合研究所, 地質調査総合センター, 研究グループ長 (40358312)
Project Period (FY)	2017-06-30 – 2019-03-31
Keywords	微動アレイ探査 / 表面波探査 / ノイズ補正 / 表層地質 / 浅部速度構造 / 平均S波速度
Outline of Final Research Achievements	We performed microtremor observation with a miniature seismic array with radius less than 1 m at exactly the same site as the previous surface-wave-exploration site in order to evaluate the accuracy of a miniature microtremor array method for a depth range from 1 to 10 m. The experimental site was set on an artificial ground at Itako City, Ibaraki, Japan. From the comparison between those phase velocities, we found that the shallower limit of the analyzable depth range for a miniature microtremor array method with radius of 0.6 m lies at about 1 to 2 m in depth. However, it was also revealed that, since the excitation modes of the surface wave were different between those methods, the exact comparison of the phase-velocity dispersion curves was difficult. For this reason, we planned and completed additional research, (i) to develop two kinds of approaches to inferring an S-wave velocity structure and (ii) to correct the incoherent noise for identifying phase velocities.
Free Research Field	社会システム工学、安全工学、防災工学およびその関連分野
Academic Significance and Societal Importance of the Research Achievements	表面波探査（SW）法による位相速度分散曲線の比較に基づく極小微動アレイ（MMA）の浅い側の解析限界は、観測仕様、観測機材に依存するものの、本検討の場合は深さ1～2m程度と考えられた。また、それぞれの分散曲線に基づくS波速度構造の比較によれば、SW法とMMA法は、逆解析精度の範囲内で同様な結果を与える。上記の結果に基づけば、探査対象が深さ2m以上ならば、微動の極小アレイは、表面波探査に必要となる観測機材や時間を削減できる代替法となり得る。現実には地盤の相違によるばらつきがあると考えられるが、本研究により、MMA法の新たな需要を創出するための探査限界のオーダーを把握できたと考える。