Earthquake risk assessment

Abstract

The assessment of earthquake risk in portfolio, urban or regional scale constitutes an important element in the mitigation of economic and social losses due to earthquakes, planning of immediate post-earthquake actions as well as for the development of earthquake insurance schemes. Earthquake risk assessment methodologies consider and combine three main factors: earthquake hazard, fragility/vulnerability and inventory of assets exposed to hazard. These factors exhibit aleatory and epistemic uncertainties embedded in their various components. Challenges exist in the characterization of the earthquake hazard as well as in the determination of the fragilities/vulnerabilities of the physical and social elements exposed to the hazard. The simulation of the spatially correlated fields of ground motion using empirical models of correlation between intensity measures is an important tool for hazard characterization. Vulnerability relationships for physical elements, derived from empirical, analytical or expert opinion based methods, provide the probability of loss ratio, conditional on a level of intensity measure. The uncertainties involved in these relationships and especially the correlation in these uncertainties are important to obtain the bounds of the expected losses. Rather simplified procedures exist for the rapid post-earthquake assessment of physical, social and economic losses. The reduction of the uncertainties inherent in the basic ingredients of such rapid earthquake loss assessment is an important issue that needs to be tackled in the future for their viability and reliability. The uncertainties inherent in the determination of exposed assets and their fragilities/vulnerabilities needs to be tackled in the future for the viability and reliability of such rapid loss assessments. The commonly used risk metrics in earthquake insurance are the Average Annual Loss and Loss Exceedance Probability curves. A rigorous treatment of uncertainty and correlation are needed for the proper estimation of these metrics and earthquake insurance related decisions. This paper looks at the current practices in regional and urban earthquake risk assessment, discusses current issues and provides illustrative applications.