| 講演要旨(和文) | | 2011年東北地方太平洋沖地震では各地で深刻な液状化が発生した．その大規模液状化の模式地の一つである幕張海浜公園において，液状化のメカニズムを明らかにすることを目的とした浅部地盤構造調査を実施した．同公園内4箇所においてオールコアボーリングを実施し，表層15mまでの地質構成を確認した．加えて7箇所でCPT/SCPTを実施した．さらに120mの探査測線を2本設定し，高精度表面波探査と高分解能S波反射法探査を実施した． 地質調査結果から，液状化発生層は深さ3-6mに分布する浚渫土層に比定された．物理探査の結果では深さ3-5m付近にS波の低速度層が認められ，この調査結果と調和的であった． |
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| | 講演要旨(英文) | | Integrated geological and geophysical investigations were conducted at Makuhari-Kaihin Park where significant sand boiling from fissures was observed accompanied with liquefaction caused by the 2011 East Japan Earthquake. The park was reclaimed just after the 1987 East off Chiba Prefecture Earthquake using dredged fine sand and the surface was covered with clayey fill soils up to 5 m in thickness. Because the boiling sand is characterized by fine sand including large amount of shell fragments, it was presumed to be originated from the dredged sand layers. However near-surface geology was still unknown and there were few available drill data around the park. To clarify the near-surface structure and its geophysical properties, we conducted high-resolution near-surface geophysical surveying at the park. As a result, a low S-wave velocity layer was identified at the dredged sand horizon about 3 to 5 m in depths. The survey results shows that it is capable to delineate liquefied layers as anomaly zones in geophysical profiles. |
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