Tectonic setting of the Azores Plateau deduced from a OBS survey

The studies of Azores seismicity generally show shocks with either normal f aulting or right-lateral strike-slip along the ESE direction, compatible wi th a eastward relative motion of the Eurasian (EU) relative to the African (AF) plate. However, the 1 January 1980 earthquake was interpreted as a cle ar left-lateral strike-slip shock along the N150E direction. This pattern i s difficult to explain in terms of the relative motion between the EU, AF a nd North American (NA) plates: all available models for the present day mov ement of this triple junction fail to explain the regional variability in t he stress conditions of the area. Here we present data from a 34-day long O cean Bottom Seismograph array deployment. We show that the seismicity is di stributed along a band aligned with the island chain itself, and is concent rated along several faults with an approximate N150E strike, cutting the Az ores plateau in all the area covered by the OBS network. The combination of these new results with other geophysical data permits us to conclude that the tectonic setting of the Azores plateau is characterised by the existenc e of two sets of faults, in the N120E and N150E directions, defining severa l crustal blocks, whose relative motion accommodates the interaction of the three megaplates. The deformation of these tectonic blocks is probably dri ven by the shear between the EU and AF plates. This model explains well the spatial variability of the stress conditions in the Azores domain, the com bination of dextral and sinistral strike slip mechanisms and the observed s eismotectonics of the Azores islands.