| 講演要旨(和文) | | 2011 年3 月11 日に発生した東日本大震災発生時，東京湾岸や利根川下流域においては広い範囲で液状化被害が発生した．この被害領域は広範囲にわたり都市域であるため，全域で高密度にボーリング調査や土壌サンプリングが困難である．そのためにわれわれは，物理探査手法を適用し，ボーリング調査結果を空間的に補間する研究を実施している．この研究により，少ない本数のボーリングにより地下構造把握や液状化予測が可能となることが期待される．その研究の一環として，比較的広範囲に液状化被害を受けた茨城県潮来市において，深度約50m程度までの地下構造把握を目的として，S波反射法地震探査および表面波探査を実施した．その結果，日の出地区およびその周辺の地下構造が明らかになった．表面波探査のS波分布より調査地域は，比較的高速度な表層，その下位の低速度層および最下位の高速度層で特徴付けられることがわかった． |
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| | 講演要旨(英文) | | The Great East Earthquake occurred on March 11, 2011 caused serious damage to people's lives not only by the direct damage of an earthquake but also by the tsunami, subsidence, and liquefaction. In particular, in Tokyo Bay area and the Tone River downstream region, liquefaction damage occurred in the wide range. Since the domain damaged reaches far and wide this time and since the area had been highly developed with dense population and buildings, it was difficult to carry out drilling surveys and soil samplings in the whole region with sufficient density. Therefore, we conduct researches to interpolate drilling survey results spatially by applying the geophysical survey technique which can image subsurface structure nondestructively from the ground surface. By this research, it is expected that subsurface imaging and liquefaction prediction will be attained by a limited number of drill holes. As a part of the research, we carried out the S wave seismic reflection survey and the surface wave survey for imaging subsurface structure down to the depth of about 50 m in Itako, Ibaraki which suffered widespread liquefaction damage. The surface layer with comparatively high velocity can be interpreted as the sandy dredged soil, the low velocity layer as the Hinode Mud Formation, and the high velocity layer as sandy part of the Sawara Alternating Layers of sand and mud. |
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