Abstract
In Japan, each prefecture selects some scenario earthquakes, and uses them for making a regional disaster prevention plan. They select scenarios which cause the largest loss, but the scenarios' event probabilities are not considered. It is too conservative and uneconomical to plan a regional disaster prevention for a scenario which has a very low event probability. “Hazard-consistent scenario earthquake” was proposed as a method of selecting scenario earthquakes based on probability. But this method is not appropriate to be used for planning a regional disaster plan because this method is based on a hazard analysis at only one point. So, for example, this method can't distinguish a case where a seismic intensity of 5 upper is observed in only small area from a case where it is observed in almost all area in a region. “Risk-consistent scenario earthquake” (Ishiskawa & Okumura, 2001) can avoid this problem. But in a previous study, each risk curve of prefectures is calculated based on an assumption that all houses have been built at a prefectural capital. In this study, “PEX-consistent scenario earthquakes” is proposed. This is a new method of probabilistic scenario earthquakes based on the relationship between population exposure to seismic intensity (PEX) and its exceedance probability (P-PEX relation). Population distribution is thought to be positively correlated with various social wealth, so PEX represents simply an effect of earthquakes. The Proposal method consists of three steps. First, calculating P-PEX relation and each seismic zones’ contribution for it. Second, determining the seismic zone corresponding to the target risk level. Third, determining a seismic intensity distribution of the background earthquakes corresponding to the level. Following results are obtained in this study. 1) In almost all prefectures, background earthquakes are included in scenario earthquakes corresponding to the specific risk level. But only about 20 prefectures consider background earthquakes in their loss estimations. 2) In Tokyo, the seismic intensity distribution of intraplate earthquake of Philippine sea plate corresponding to 100 yr. return period is lower than the scenario of Tokyo prefectural government, and the distribution corresponding to the 2500 yr. return period is very much higher than it.
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