Abstract
The history of the Azores archipelago, from its discovery and settlement in the first half of the 15th century through the present, is marked by the social and economic impacts produced by earthquakes, mainly the high-intensity ones. Information that has been compiled leads to the conclusion that in this period, 33 earthquakes with intensity equal to or greater than VII have affected the Azores, which caused approximately 6,300 deaths and widespread destruction on some islands of the archipelago, principally S. Miguel, Terceira, Graciosa, Faial, S. Jorge and Pico Islands. The accommodation of strain resulting from the dynamics of the Azores triple junction (ATJ) plate boundary and volcanism, which also occurs in the region, are the main factors responsible for the intense seismic activity in this archipelago. This work reviews the scientific issues of the known earthquakes that have severely interfered with the lives of the Azorean people throughout their history, which we call large earthquakes.
Highlights
The historical information available, which describes the destructive effects caused by earthquakes, shows spatial and temporal gaps that are due in large part to the geographical distribution of the population
The epicentre map of instrumental seismicity (Fig. 1) shows the branches of the triple junction of the Azores region well defined to 24° W, along a sector that includes the Azores Plateau (AP) and extends from the Mid-Atlantic Ridge (MAR) to 24o W
The high level of seismicity along the MAR and the Terceira Rift (TR) (Fig. 1) is strongly associated with seafloor spreading and the northeastward motion of the Eurasian plate with respect to the African plate (Luis et al, 1994).This argument was supported by Fernandes et al (2002), who proposed an elastic model with two possible locations of the Azores triple junction: along the extension of the TR at the same latitude as Graciosa Island or on the Faial fracture zone at the same latitude as Faial Island
Summary
The historical information available, which describes the destructive effects caused by earthquakes, shows spatial and temporal gaps that are due in large part to the geographical distribution of the population. (Oliveira, 1986), in the Azores region, such information is not available before the beginning of the sixteenth century, when a sizable population began to occupy the islands. Miguel Island, and buried that capital, not being saved of her more than a small suburb of the West side, and two houses on the beach Of these places there survived little more than seventy people.... In addition to the destruction of a large part of the housing stock in Faial and the eight deaths, the earthquake damaged approximately 20% of the houses on the neighbouring island of Pico These are three descriptions of the many possible ones regarding the consequences of the earthquakes, sometimes with relatively low magnitudes, that throughout history have perturbed the stability of the Azoreans. Considering that the focal mechanisms of recent significant earthquakes are the information basis to understanding geodynamic and seismotectonic models of the Azores, this issue will be addressed in the current study
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