Seismic activity in the Azores Region in the contexto of the western part of the Eurasia-Nubia plate boundary

Abstract

The western part of the Eurasia-Nubia plate boundary, with different tectonic features, extends from the Azores Islands to the Strait of Gibraltar. Based on focal mechanisms of large earthquakes, we observe the conversion of an extensional regime (Strike-slip and normal dip-slip motion) near to the Azores to a compressional regime (strike-slip and reverse dip-slip motion) in the east of the Atlantic Ocean (Gulf of Cádiz). The character of this plate boundary is defined by a clear seismicity, which is mainly controlled by the tectonic activity existing along the Azores Gibraltar Fracture Zone (AGFZ), which extends from the Azores Islands to the Strait of Gibraltar. Seismic activity and moment tensor solutions of earthquakes indicate that present-day interplate collisional coupling in the Western Mediterranean region is most pronounced in western Iberia and the offshore Atlantic marked by NW to N-directed horizontal compressional stresses. This is also reflected by the occurrence of large historical and instrumental earthquakes, in particular by the recent earthquakes occurred on 1980 (Mw=6.8), 1997 (Mw=6.2), 1998 (Mw=6.2) and 2007 (Mw=6.3, Mw=6.1) in the Azores Islands and on 1969 (Mw=7.8) and 2007 (Mw=6.1) off coast of South-Western Portugal. In this work we discuss the seismic activity of the Azores region in the context of the Eurasia-Nubia plate boundary.