DEVELOPMENT OF RISK EVALUATION METHODCONSIDERING AFTER SHOCKS
Keywords:Aftershock, Risk evaluation, Seismic risk, Multi-event model, Risk curve
As shown in 2016 Kumamoto earthquake, it has become an issue that the damage or loss by aftershocks is greater than those by main shock. This situation is caused by the following two facts; the ground motion intensity by aftershocks are larger than that by main shock depending on the locations of aftershocks, and capacity of buildings is reduced by main shock. This paper proposes the methodology to probabilistically evaluate risks, such as loss or damage rate, considering the aftershocks. The methodology employed is the multi-event approach in which numerous events are generated with their location, shape, magnitude and occurrence probability so that the risk of not only a single building, but portfolio of buildings can be evaluated. This paper adds two features on the method; one is generating the conditional aftershock events, and the other is reducing the capacity of buildings reflecting damage status by main shock event. Model buildings located in the area where the effects of aftershocks cannot be ignored is used for application simulation with three conditions; no aftershocks, followed by aftershocks without capacity degradation, and followed by aftershocks with capacity degradation. The deference in the risks are evaluated by the risk curves. Through the simulation it is concluded that the proposed method can evaluate the risks considering aftershocks adequately.