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Instituto de Investigação
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Referência Bibliográfica

GOMES, A., GASPAR, J.L., QUEIROZ, G., FERREIRA, T. (2008) – Impact of geological hazards at Sete Cidades Volcano (S. Miguel Island, Azores): A first quantitative approach. IAVCEI 2008 General Assembly, Reykjavik, 17 - 25 de Agosto (Poster).


The Azores archipelago, located on the North Atlantic Ocean, is formed by 9 volcanic islands. Since its settlement, on the XV century, several volcanic eruptions, strong earthquakes and landslides were responsible for thousands of casualties and important damages. Sete Cidades is an active central volcano with caldera located in the western part of S. Miguel Island with a tectonic regime dominated by the NW-SE regional fault system and less evident E-W and NE-SW faults. In the last 5000 years at least 17 explosive eruptions occurred centered inside the caldera, which makes it one of the most active volcanic centers in Azores. To study the impact of the different geological hazards in Sete Cidades area a field survey was carried out in order to verify the dwellings vulnerability in 10 parishes located around the volcano and inside the caldera, where, according to Census 2001, 11 429 persons live. The analysis of the recent volcanic activity (< 5000 years) and associated eruptive styles showed that most of the events were VEI 4 and had important hydromagmatic phases (Queiroz, 1997; Cole et al., 2008; Queiroz et al.; 2008) The occurrence in present days of an eruption with similar character implies that around 88% of the study area will be affected with tephra deposits thickness higher than 2 m, and 12% with thickness between 1 m and 2 m. For earthquake activity, the study demonstrated that if Sete Cidades region is affected by an event with intensity VII (EMS-98), between 54% (6 155) and 77% (8 834) of the population will need to be relodged. However, if the seismic intensity attains the degree X (EMS-98) the number of persons dislodged increase significantly, among 89% (10 124) and 94% (10 722). The analysis of the landslide susceptibility allowed verifying that around 53% of the study area is classified with moderate landslide susceptibility and 33% with high to very-high susceptibility. Around 65% of the dwellings are built on areas with moderate landslide susceptibility and 21% on zones with high to very-high susceptibility. The results from this work in Sete Cidades volcano region raise the importance of geological hazards studies for emergency and land use planning purposes.