Abstract
With the earthquake records obtained during the last 23 years, analyses of the transfer function, the cross spectrum and the coherence function have been carried out for a rockfill dam, called Aratozawa dam (74.4m high and with central clay core). Based on analysis results the fundamental frequencies and acceleration amplification factors of the dam body are investigated. It is found that the fundamental frequencies and the acceleration amplification factors of the dam body sharply declined temporarily, shuck by the Iwate-Miyagi Nairiku Earthquake, June 14, 2008. However, these characteristics almost recovered to their original status about a week after the main shock. As for the propagating behavior of the seismic waves in the dam-foundation system, it has been pointed out that in the low frequency domain up to the fundamental frequency of the dam, the response of the dam crest mainly depends on the seismic motions of the lower bedrock. On the other hand, in the higher frequency domain, the contribution from the seismic motions of both banks may become dominant at some frequencies. It has been also found that such features temporarily changed due to the mentioned strong earthquake.
