| 講演要旨(和文) | | 2016熊本地震で甚大な被害を被った熊本県益城町において，道路・堤防上に測線を設定して盛土構造物と表層地盤を対象とした浅部物理探査を実施した．適用した手法はハイブリッド表面波探査，オームマッパー電気探査および地中レーダ探査である．解析の結果，地表断層通過位置とは異なる部分に低速度帯を見出した．比抵抗構造にも南東側上がりの構造が認められ，横ずれだけでなく鉛直累積変位があることがわかった． |
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| | 講演要旨(英文) | | We conducted a dense near-surface geophysical survey at an area stricken by the 2016 Kumamoto Earthquakes. The survey comprised Hybrid Surface Wave Survey (HSWS), capacitively coupled resistivity (CCR) measurement using OhmMapper, and GPR measurements. A total of 5 short lines were set to intersect a branched surface rupture, or placed in the downtown area of Mashiki Town. Survey's purpose was to assess the usefulness of the survey methods for the delineation of near-surface conditions of such earthen structures as levees and road embankments attacked by strong earthquakes. Notable results of our study were as follows. First, GPR successfully imaged detailed structures on the surficial zones up to 2 to in case to 5 m in depth. CCR surveys provided detailed resistivity profiles up to 10 m in depth. HSWS reconstructed S-wave structures which clearly delineated low velocity zones around the intersecting portion with the surface rupture. The S-wave velocity profiles strongly suggested that surface rupture did not reflect earthquake faulting at depths. In addition, HSWS records were processed through an ordinary seismic reflection data processing flow. As a result, faulting structure in a zone of several 10 meters wide was clearly imaged in concordance with the other near-surface survey results. |
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