ABSTRACT
There are about 210 thousands irrigation tanks in Japan, which have been the important sources of water supply for farming since ancient times. But most of the tanks were constructed many years ago and damaged so much. Kato (2005) reported that about 20 thousands irrigation tanks needed to be repaired. Due to the decrease in the population of farming areas and the increase of aging farmers, many tanks are not well controlled. Under such a circumstance, if a big earthquake or a heavy rain by typhoon is encountered, the damage probability of embankments of irrigation tanks would be very high. In past years, many irrigation tanks were damaged by earthquakes. Tani (2002) summarized the number of the irrigation tanks damaged by past each earthquake. In 1995, 1222 irrigation tanks were damaged by South Hyogo prefecture earthquake. The maintenance and the repair of irrigation tanks are the important to prevent the damage from such a disaster. It is important for the maintenance and the repair to analyze the actual some damages of the irrigation tanks by an earthquake. Some studies have been made on the analysis of the seismic damage of irrigation tanks in Japan. Yamazaki et al. (1989) analyzed the seismic damage of irrigation tanks for Nihonkai-chubu earthquake in 1983 in statistical approach. In statistical approach, it is easy to deal with many targets. On the other hand, many studies have been made on the seismic damage of the individual irrigation tanks or the earth dams by numerical analysis which includes finite element model (FEM). These analyses need much time, therefore it is difficult to analyze many targets.
