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The Eurasia–Nubia plate boundary between the Azores and the Strait of Gibraltar has been the place of large tsunamigenic earthquakes. The tectonic regime is extensional in the Azores, transcurrent along the Gloria Fault, and compressional in the Strait of Gibraltar. Here, the plate boundary is not clearly defined. The knowledge of past events that occurred in the area constitutes an essential contribution to the evaluations of seismic and tsunami hazard in the North-East Atlantic. In this study, we present an overview of the six major events in the area and show the use of tsunami data to add some constraints on their source. The historical events occurred in the eighteenth-century between 1722 and 1761, while the twentieth-century events occurred between 1941 and 1975. We speculate that major tsunamigenic earthquakes that occur in the Iberia-Maghreb area take place at the boundaries of a lithospheric block approximately defined by the location the six events summarized here, which role and dynamics are not yet understood. [ABSTRACT FROM AUTHOR]

On 8 May 1939, an earthquake (Ms7.1) occurred near the Azores archipelago, with an epicentre located close to the western end of the Gloria fault. Previous studies present different epicentre locations spreading over a large area, and two different types of focal mechanisms. Given these uncertainties, the interpretation of the seismological information in a complex tectonic environment between the Gloria Fault and the Terceira Ridge is a matter of debate. The event caused a small tsunami recorded in the Azores Islands. In this study, we use the tsunami observations and tsunami numerical modelling to select the earthquake fault rupture that best fits the tsunami observations. We consider the different focal mechanism solutions, perform tsunami numerical modelling, and compute synthetic tsunami waveforms at the tide gauge locations. We find that an earthquake caused by a low-angle dipping fault with dominant strike–slip movement generates a tsunami that reproduces well the record at Ponta Delgada tide gauge. Finally, in areas where earthquakes are rare, the study of ancient earthquakes must use all information available, namely tsunami observations and mareograph data. [ABSTRACT FROM AUTHOR]