Author(s)

MARIA JOÃO BARROS, MARGARIDA MACHADO PIRES

Abstract

The Azores, a nine island Portuguese archipelago located in the north Atlantic Ocean, between North America and Europe, in the Azores micro-plate, is an area of severe seismic activity, due to its geotechnical framing and volcanic activity. Earthquakes are inevitable, but their consequences are not. Since the hazard cannot be reduced, we have to reduce exposition and building stock vulnerability, to mitigate seismic risk. The purpose of this paper is to assess the seismic vulnerability and the average estimated damage grade, for moderate to high seismic intensities, of the residential building stock in São Miguel Island, Azores, based on a representative sample of buildings. Since buildings are not all the same, we can expect different consequences/damages on buildings facing the same earthquake. So, to have a detailed characterization of the building stock, regarding the structural characteristics and conservation state, a residential building stock survey was used. Four different classes of vulnerability were defined based on the survey and on historical data related to destruction that occurred during seismic events faced on other Azorean islands, namely the event which affected the islands of Faial and Pico in 1998. The vulnerability index was calculated for each building in the sample based on a series of eight relevant parameters. A weight was assigned to each parameter according to its importance. For each one of the parameters, the four vulnerability classes were considered. Afterwards, the mean damage grade was evaluated for each building. Finally, the average global vulnerability index and the estimated damage grade were calculated, for moderate to high seismic intensities. The results of this study are as expected when compared with a previous study performed in Faial. This methodology can be used on other islands and repeatedly with updated data as a powerful tool for local authorities.

Keywords

São Miguel Island, Azores, building stock, seismic vulnerability, vulnerability index, damage grade