Aftershock sequence of the January 1st, 1980, earthquake and present-day tectonics in the Azores

The composite focal solution of a 7‐days aftershock sequence to the M 7.2 Azorean earthquake shows a quadrantal repartition of first motions similar to those of all former major earthquakes on this western part of the Azores‐Gibraltar line. However for the first time is the choice of the fault‐plane constrained, the spatial repartition of aftershocks indicating the slip direction to be N 150°E, with sinistral shear. Interpretations of all former shocks had chosen the conjugate nodal plane as fault‐plane, dextral shear along this direction seeming coherent with the difference in average spreading rates North and South of the Azores and approximate direction of the Europe‐Africa plate boundary. The direction of rupture documented here coincides with the volcano‐tectonic directions dated as recent by Féraud et al. (1980). This supports a model in which the island volcanism would be tectonically controlled by the direction of rupture of earthquakes.