A Study on Modeling of Earthquake Disaster Risk Indices and Application to Circular Water Utilization System in Large Urban Area

Abstract

It has been expected that a big earthquake will occur in the near future at many cities where more than 500 thousand people live in Japan. Therefore several measures for preventing and mitigation of disaster have already been taken. However, most of these measures had no effect at the time of the Hanshin-Awaji earthquake. It was the reason that circular water utilization network system including waterworks networks and sewerage networks and river systems has not been considered at all.In this paper, a hierarchical model of circular water utilization system with 4 layers (a river layer, a water supply layer, an urban active layer, and a sewerage layer) is firstly proposed. Each layer is consisted of elements such as intake facilities, water purification plants, and sewage plants and so on. With the aid of this system model, earthquake disaster risks are classified.Secondly, earthquake disaster risk indices are set up. The concepts of stability and safety of water circulation networks are introduced and modeling considering with so large and complex system, that is, stability is modeled with graph theory and safety is modeled statistically (not mechanically). Stability indices were already discussed and published, so safety indices are mainly discussed in this paper. Then, earthquake disaster risk diagnosis that is consisted of stability and safety indices is introduced. It could be called a type of multi-dimensional criteria analysis.Finally, earthquake disaster risk diagnosis proposed is applied to Yodo River circular water utilization system including Kyoto, Osaka and Kobe, where population is more than 13 million, as a case study. As a result, both the indirect and direct damage in this region in question at the occurrence of an earthquake are clarified by using stability and safety indices and the areas with high earthquake disaster risk for water supply and expected environmental pollution disaster are pointed out. Consequently, it is shown that our proposed evaluation indices of earthquake disaster risk diagnosis are effective against future great earthquakes.