Regional earthquake loss estimation : role of transportation network, sensitivity and uncertainty, and risk mitigation

Abstract

Large earthquakes near densely populated areas such as the 1994 Northridge and 1995 Kobe events have caused extensive damage to the physical infrastructure and losses to the regional and national economies. Economic losses are due in part to direct damage and in part to business interruption caused by non- functioning infrastructure and interdependencies among industrial sectors. We developed a regional earthquake loss methodology that emphasizes economic interdependencies at regional and national scales and the mediating role of the transportation network. In an application to the Central U.S. under threat from earthquakes from the New Madrid Seismic Zone, we (1) evaluate regional and national losses from scenario earthquakes, (2) quantify uncertainty on the losses through loss risk curves including contributions from seismicity, attenuation, fragilities, etc. and (3) assess the effectiveness of alternative mitigation strategies. The loss assessment methodology includes spatial interactions (through the transportation network) and business interaction (through an input-output model) and extends geographically to the entire conterminous U.S. The losses reflect damage to buildings and transportation components, reduced functionality, changes in the level of economic activity in different economic sectors and geographical regions, and the speed of the reconstruction/recovery process. Evaluation of losses for a number of scenario earthquakes indicates that losses from business interruption may be as significant as infrastructure repair costs. The overall loss is also contributed by the increase in transportation costs due to network damage.

(cont.) As part of the uncertainty evaluation, we assess the sensitivity of earthquake losses to various component models and model parameters. Using a detailed model of regional seismicity, scenario earthquake building losses, and a relation between business losses and building losses, we develop risk curves for building losses, business losses, and total economic losses. The results underline the importance of considering uncertainty in risk assessment. Finally, we investigate the effectiveness of alternative loss mitigation strategies such as retrofitting of buildings or bridges and faster recovery of functionality for various occupancy classes or bridges. For a number of cases, we develop loss risk curves for mitigated conditions and calculate expected annual losses, which might be used for rational decision making e.g. through cost-benefit comparison.