Abstract
We investigated the time-dependent change of soil response at three KiK-net vertical array sites for several years before and after the 2011 off the Pacific coast of Tohoku earthquake by means of a simple quantitative index of soil nonlinearity. The whole site showed significant nonlinear soil response during the mainshock of the 2011 Tohoku Earthquake. We focused on the soil response recovery process at these sites after the mainshock. The soil response characteristics at MYGH10 recovered to those before the mainshock faster than TCGH16, though both the sites were attacked by strong ground motions over 1 G during the mainshock. The soil response at FKSH14, where the spiky waveforms implying cyclic mobility were observed during the mainshock, also showed the slower recovery similar to TCGH16; the soil response recovery at these sites does not completed even three years after the mainshock. The difference of the soil response recovery at the three sites would be attributed to the difference of their soil characteristics.
