Vol.2 No.3 2009

Research paper : Evaluation of earthquake occurrence from active faults (T. Yoshioka)−180−Synthesiology - English edition Vol.2 No.3 (2009) this Full Research.We assessed the active faults that were 20 km or more throughout Japan, and 547 behavioral segments were categorized. Of these, the parameters such as average displacement rate, amount of slip in an earthquake, and past rupture periods were estimated based on existing data for 295 behavioral segments that were 10 km or more long and had some degree of rupture level, and their future rupture probabilities were calculated. The behavioral segments grouped by color according to the rupture probability were plotted on the map of Japan (Fig. 5).The Rupture Probability Map of Major Active Faults in Japan was published by the Geological Survey of Japan, AIST in September 2005. This map enabled comparison of the active faults under a uniform criterion for the entire country, although there were variations in confidence due to the fineness of data by region. As comparison became possible under a uniform criterion for the whole of Japan, it has been used for risk assessment by the insurance industry and by the regional infrastructure planners. By indicating the assessment criterion for individual behavioral segments, it could be used by users who need assessment based on different standards.This assessment, of course, is a research result of a single research institution, and therefore is simply one prototype. It is distinctly different in character from the long-term assessment of the Headquarters for Earthquake Research Promotion of the government, which is based on an official standard determined by a committee. Therefore, the figures shown differ greatly in some places, and some people have voiced concerns that this may cause confusion in society. Also, since the results are based on estimated values using provisional and empirical values, many researchers (particularly those of geomorphology and geology) who place importance on individual data commented that faults with insufficient data should not be assessed.However, considering the difficulty of assessing the actual earthquake occurrence, it is natural that various assessment results exist, and we thought it was important to present figures as one of the assessment results.As a result, the Rupture Probability Map of Major Active Faults in Japan obtained a certain degree of acclaim from the insurance industry, and we received several inquiries about using this assessment as basic data. It can be said that it is having some social impact.4 Limitation of prediction and future issuesAlthough the Rupture Probability Map of Major Active Fig. 5 Rupture Probability Map of Major Active Faults in Japan[8] (close up of the Kinki area).The numbers show the behavioral segment numbers.136°E35°N136°E050 kmLegendRupture probability for the next 30 years according to the BPT distribution model (categorization by color)0.3 % or more, less than 3 %0.03 % or more, less than 3 %Less than 0.03 %3 % or moreUnknownRecurrence interval (categorization by thickness)3,000 years or less3,001~10,000 years10,001 years or moreBehavioral segments without activities after the Late Pleistocene periodBehavioral segments that were not subjects of probability calculation


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