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Instituto de Investigação
em Vulcanologia e Avaliação de Riscos
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Artigos em livros de actas ► Internacionais


Referência Bibliográfica

SILVEIRA, D., GASPAR, J.L., FERREIRA, T., QUEIROZ, G. (2002) - Maximum historical seismic intensity map of S. Miguel island (Azores). Geophysical Research Abstracts. 27th General Assembly of the European Geophysical Society.


The Azores archipelago is situated in the Atlantic Ocean where the American, African and Eurasian lithospheric plates meet. The so-called Azores Triple Junction located in the area where the Terceira Rift, a NW-SE to WNW-ESE  fault system with a dextral component, intersects the Mid-Atlantic Ridge, with an approximate N-S direction, dominates its geological setting.


S. Miguel Island is located in the eastern segment of the Terceira Rift, showing a high diversity of volcanic and tectonic structures. It is the largest Azorean island and includes three active trachytic central volcanoes with caldera (Sete Cidades, Fogo and Furnas) placed in the intersection of the NW-SE Terceira Rift regional faults with an E-W deep fault system thought to be a relic of a Mid-Atlantic Ridge transform fault. N-S and NE-SW faults also occur in this context. Basaltic cinder cones emplaced along NW-SE fractures link that major volcanic structures. The easternmost part of the island comprises an inactive trachytic central volcano (Povoação) and an old basaltic volcanic complex (Nordeste).


Since the settlement of the island, early in the XV century, several destructive earthquakes occurred in the Azores region. At least 11 events hit S. Miguel Island with high intensity, some of which caused several deaths and significant damages.


The analysis of historical documents allowed reconstructing the history and the impact of all those earthquakes and new intensity maps using the 1998 European Macrosseismic Scale were produced for each event. The data was then integrated in order to obtain the maximum historical seismic intensity map of S. Miguel. This tool is regarded as an important document for hazard assessment and risk mitigation taking in account that indicates the location of dangerous seismogenic zones and provides a comprehensive set of data to be applied in land-use planning,emergency planning and building construction.