Comparison and modelling of building losses in South Iceland caused by different size earthquakes

Abstract

In June 2000, two earthquakes of Mw6.52 and Mw6.44 occurred with a 4-day interval in the South Iceland seismic zone, and in May 2008, a Mw6.30 earthquake occurred further west in the zone. Their epicentres and fault ruptures were close to small towns and farms, and almost 5000 residential buildings were affected in each of these two seismic events. Despite substantial damage, no residential building collapsed and there were no fatalities. Catastrophe insurance of buildings is mandatory in Iceland. Driven by insurance claims, repair cost was estimated for every affected building, and registered in two independent datasets, called hereafter the 2000 and the 2008 dataset. Two complete loss datasets from different size earthquakes, affecting the same building typologies in the same region is rare to find in the literature. Valuable information can be drawn by comparing the losses caused by these events on the housing stock. In this study an advanced empirical vulnerability model based on zero-inflated beta regression was fitted to five building typologies, based on GEM taxonomy, independently for the 2000 dataset and the 2008 dataset. The peak ground acceleration (PGA) was used as intensity measure. The vulnerability model and the fragility curves are substantially different from these two datasets. For a given PGA, the mean losses based on the 2000 dataset was typically roughly twice that based on the 2008 dataset. Such a large difference in losses for similar building types located in the same area indicates that PGA is not alone an adequate intensity measure to predict losses. The study also showed that high code buildings performed better than low code buildings.