Isolation risk analysis of residential settlements in mountainous region: case studies for 2004 Niigata-Ken Chuetsu and 2016 Kumamoto earthquakes

Abstract

Road networks in mountainous areas are critical infrastructures to maintain social activities. Slope failures triggered by an earthquake often disrupt the functionality of road networks. For example, during the 2004 Niigata-ken Chuetsu Earthquake, in Japan, Yamakoshi village isolated due to distortion of the road network and all residents were forced to move to the disaster evacuation camps outside of the town. Isolation of a residential settlement affects the damaged region not only for the short-term but also for a long-term. Therefore, prediction and countermeasures in advance are necessary. In this study, a procedure to evaluate the isolation risk of residential settlements in a mountainous region where a strong earthquake strikes. First, the road network is modeled as a set of nodes and links by the graph theory. Second, the probability of failure for each node and link is computed considering slope failures under a given earthquake scenario. Finally, the isolation risk is evaluated by conducting the connectivity analysis with the Monte-Carlo simulation, For validation of the presented procedure, case studies for the 2004 Niigata-ken Chuetsu earthquake and the 2016 Kumamoto earthquake are conducted.