Abstract
We conducted Normalized Input-Output Minimization (NIOM) method for the long-term earthquake observation records at Aratozawa Dam located in Miyagi Prefecture, and examined the temporal changes of the propagation time of seismic waves in the dam body. The examinations revealed that (1) the S-wave propagation time observed during the 2008 Iwate-Miyagi Nairiku earthquake showed an abrupt increase due to the nonlinear behavior of the dam body; (2) a similar increase was observed during the 2011 off the Pacific coast of Tohoku earthquake, however, the amount of the increase was smaller than that found during the Iwate-Miyagi Nairiku earthquake, and the effects to the dam body due to the Tohoku earthquake was not significant; and (3) a gradual decrease of the propagation times proportional to the logarithms of lapse time was observed after the mainshocks of the 2008 Iwate-Miyagi Nairiku earthquake and the 2011 off the Pacific coast of Tohoku earthquake.
