Evaluation of strong ground motion at Imagawa, Urayasu City, during the 2011 off the Pacific coast of Tohoku Earthquake

Serious damage due to ground liquefaction occurred in Urayasu City, located in the coastal area around Tokyo Bay, during to the 2011 off the Pacific coast of Tohoku Earthquake (Mw 9.0). In particular, extensive liquefaction was observed in the Imagawa District of Urayasu City. In order to investigate the mechanism of damage and to establish appropriate countermeasures, it is very important to evaluate the strong ground motion in the Imagawa District. For this purpose, aftershock observations and microtremor measurements were carried out in and around the Imagawa District. Then, site effects in the Imagawa District were evaluated based on the microtremor H/V spectral ratios and the aftershock records.