Characterization of the tectonic origins of historical and modern seismic events and their societal impact on the Azores Archipelago, Portugal

AbstractThe Azores archipelago is located in the North Atlantic Ocean and consists of nine volcanic islands distributed along a general WNW–ESE trend, crossing the Mid-Atlantic Ridge (MAR) in the zone where three lithospheric plates (Eurasian, Nubian and North American) come across. To the west of the MAR, at the North American plate, the Corvo and Flores islands emerge from a present-day, relatively stable geological setting, while the other islands are located in an important seismically and volcanically active zone, corresponding to the boundary between the Eurasian and Nubian tectonic plates. Since the settlement of the Azores archipelago, in the mid-fifteenth century, several destructive earthquakes, such as the 1522 earthquake that severely affected São Miguel Island, and seismic crises with a significant destructive impact, have affected the region with intensities up to X (European Macroseismic Scale of 98 – EMS-98). The location of such events, either inland or offshore, is mainly related to the WNW–ESE structural system, which extends from the MAR to the Gloria Fault (GF). The instrumental seismic activity registered since 1997 has allowed improvements to the characterization of the present-day boundary between the Eurasian and Nubian plates.