The 1531 earthquake revisited: loss estimation in a historical perspective

In this research, the 1531 earthquake is revisited. This was one of the major earthquakes that affected Portugal and, specifically, Lisbon. According to coeval sources, between 1000 and 30,000 casualties were caused in Lisbon by this tremor. This range shows the great uncertainty regarding the real effects of this Event. Analyzing the real dimension of this earthquake is the goal of this research. For that purpose, this work proposes a methodology for analyzing the destruction of historical towns. The social consequences of the quake have also been investigated. To do so, a seismic risk simulator, called SIRCO, has been used. A thorough analysis of Lisbon, prior to 1531, has been done. Firstly, the geological characterization has been included. Secondly, the building stock has been reconstructed and characterized. Next, the buildings macroseismic vulnerability index and the buildings vulnerability curves have been calculated. Finally, all this information has been gathered together in a geographical information system. The results show that the most affected areas were those located in the lower part of the city and next to the Tagus River. The simulation carried out for the 1531 Earthquake estimates 46 immediate deaths and between 158 and 397 deaths during the first week after the earthquake. The estimated total of casualties is 1000. A description of the physical and sociological losses caused by this natural event is made.