Liquefaction Evaluation of Residential Land Using Geophysical Survey

Damage such as settlement and tilting of detached houses due to ground liquefaction has often been observed during recent earthquakes. In order to achieve the safe and sustainable residential environment, ground surveys are necessary to predict the damage due to ground liquefaction. However, it takes a long time and needs hard work to conduct conventional survey works. Alternative quick and accurate survey techniques are therefore required. In this study, we focused on the surface wave and passive linear array surveys, which are common geophysical survey methods. The surface wave survey can tell us the ground stiffness over the wide range. The latter one can give us the information from the ground surface down to a substantial depth. These survey techniques can give us the ground conditions more extensively and more quickly than conventional ones. From this background, we carried out geophysical explorations in Christchurch, New Zealand, where the earthquake on February 22, 2011 caused a lot of damage to detached houses due to ground liquefaction. The risk of liquefaction was then evaluated based on survey results. The evaluation methods using the F_L and P_L values were used for judging the liquefaction risk. As a result, the high liquefaction risk in severely damaged areas was reproduced in a short time by the results of surface wave and passive linear array explorations.