Abstract
A long period ground motion during an earthquake sometimes has a serious impact on large structures. Since the ground motion during an earthquake is largely affected by the so-called site effect which is determined by the soil structure, it is important to obtain its profile, especially the shear wave velocity profile. In this study, an attempt has been made to estimate an shear wave velocity profile by seismometer array measurements during the 2011 Tohoku earthquake and its after shocks in addition to the earthquakes prior to it, in which Chiba City was chosen as a target area. The result was compared with that of microtremor measurement and the existing profile for deep soils. It was found from the study that the phase velocity dispersion curve obtained from earthquake observations overlaps smoothly with that from microtremor measurements. It was also found that, although the estimated soil profile has a fairly good agreement with the previously reported ones, there is a possibility of a slight underestimation of the previously reported ones when compared to our result.
