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| | Abstract | | 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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