Sesimic Risk assessment of Active Fault Systems in Japan using Release Rate of Seismic Moments

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The method of seismic risk evaluation with the use of the average rate of seismic moment-release rates has been developed. to mitigate seismic hazards induced by large inland earthquakes. These inland earthquakes are generated by the movement of active fault systems. The risk evaluation method was applied to major active faults systems in central Japan and two active faults systems in the western Chugoku district. The seismic risk of the 1995 M=7.2 Hyogo-ken-nanbu earthquake was also re-evaluated by the method. It was found that the seismic risk was significantly estimated by the method. The main result is as follows ;1. The seismic moment-release rate of the Tsurugawan-Isewan tectonic line was estimated from average slip-rates of constituent active faults and magnitude of historical earthquakes. On the other hand, legeneds of submerged islands, which have been passed from generation to generation in the regions around Ise bay, were checked by historical documents and field survey. II … More was pointed out that the latest earthquake which occurred in Ise Bay was the 1586 Tensho earthquake. With use of the moment-release rate and elapsed time from the latest event to the present, the seismic risk of the tectonic line can be evaluated.2. The two active fault systems, Lake Ohara - W.Yauneyama and Iwakuni - Kamine in the western Chugoku district were defined as zones linking active and geologic faults based on distributions of active faults and historical earthquakes. The seismic risk of the active fault systems can be also evaluated from the seismic moment-release rate. It was probable that the 1997 M=6.1 Yamaguchi-ken-hokubu earthquake was caused by the movement of central part of the Lake Ohara - W.Yauneyama fault system.3. Three-dimensional geometry of active fault systems was clarified by the combination of field surveys with available microseismicity and gravity data The seismic moment-release rate which was estimated from the fault geometry is in consistent with those which was calculated from fault slip-rates and earthquake magnitude.4. It was properly evaluated by the risk assessment method that the Hyogo-ken-nanbu earthquake was generated by the movement Of the Takatsuki - Rokko - Awaji tectonic line. Less