Estimation of subsurface structure of Wakasa region based on microtremor observation

2015 Fiscal Year Final Research Report

• Project/Area Number: 25420479
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Research Field: Structural engineering/Earthquake engineering/Maintenance management engineering
• Research Institution: University of Fukui
• Principal Investigator: KOJIMA Keisuke 福井大学, 工学(系)研究科(研究院), 教授 (40205381)
• Co-Investigator(Kenkyū-buntansha): OH-HORI Michihiro 福井大学, 附属国際原子力工学研究所, 准教授 (50419272)
• Project Period (FY): 2013-04-01 – 2016-03-31
• Keywords: 常時微動 / 展開アレイ観測 / S波速度構造 / 逆解析 / 小浜平野 / 若狭町

Outline of Final Research Achievements

I formulated the inversion procedure of the S-wave structure of array sites as an optimization problem based on both generalized spectrum density function and H/V spectral ratios permitting higher-mode contamination. By evaluating two kinds of information from the array observations simultaneously, the procedure can estimate reliable underground structure. Microtremor array observations were conducted in the Wakasa region to know S-wave structures of sedimentary layers down to the bedrock. 3-components single-site microtremor observations were carried out to compensate the array observations. The 3D subsurface structures around Obama city and Wakasa town have been interpolated by using geo-statistical procedure. The validity of the estimated subsurface structure was confirmed by comparing with the density structure and with the existing seismic-reflection survey results. The estimated bedrock depth has a discontinuity of which the position is coincided with the Mikata Fault.

Free Research Field

土木工学