Abstract

Despite their relative poor precision, classical geodetic observations can provide valuable information about tectonic displacements because their lack of precision is balanced by the time span they cover. In the case of the Açores archipelago the contribution of six decades of classical observations provide a historically reliable and important source of information in the establishment of a tectonic model for that area, complementary to GPS data, where only few years of observations are available. Based upon angular and invar wire measurements carried out in the thirties, compared with more recent classical and GPS observations, the authors were able to deduce some significant displacements. For the Central Group, we conclude that the area is expanding in an approximately WSW–ENE direction, showing a component parallel to the plate boundary between Eurasia and Africa, which is about 1.5 greater than the component in the perpendicular direction. As regards the Faial and S. Jorge islands, our results show a good agreement with the proposed geodynamic models for Faial, but not for S. Jorge. For Faial, the results indicate an extension perpendicular to the faults in the direction WNW–ESE, and a dextral strike slip along the same faults. In the case of S. Jorge the lack of agreement with the proposed geodynamic models is probably due to the particular poor geometry and scale control of the inner network.

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