Abstract
Abstract. The M ∼ 8.3–8.4 25 November 1941 was one of the largest submarine strike-slip earthquakes ever recorded in the Northeast (NE) Atlantic basin. This event occurred along the Eurasia–Nubia plate boundary between the Azores and the Strait of Gibraltar. After the earthquake, the tide stations in the NE Atlantic recorded a small tsunami with maximum amplitudes of 40 cm peak to through in the Azores and Madeira islands. In this study, we present a re-evaluation of the earthquake epicentre location using seismological data not included in previous studies. We invert the tsunami travel times to obtain a preliminary tsunami source location using the backward ray tracing (BRT) technique. We invert the tsunami waveforms to infer the initial sea surface displacement using empirical Green's functions, without prior assumptions about the geometry of the source. The results of the BRT simulation locate the tsunami source quite close to the new epicentre. This fact suggests that the co-seismic deformation of the earthquake induced the tsunami. The waveform inversion of tsunami data favours the conclusion that the earthquake ruptured an approximately 160 km segment of the plate boundary, in the eastern section of the Gloria Fault between −20.249 and −18.630° E. The results presented here contribute to the evaluation of tsunami hazard in the Northeast Atlantic basin.
Highlights
The western segment of the Eurasia–Nubia plate boundary extends from the Mid-Atlantic Ridge in the Azores towards the Strait of Gibraltar
We used the travel time of the first wave arrival at each station to compute a preliminary location of the tsunami source
The location of the tsunami source is the minimum of the averaged travel time square errors
Summary
Among these events are those that occurred on November 1941 (Udias et al, 1976; Lynnes and Ruff, 1985), 9 June 1969 (Argus et al, 1989), May 1975 (Buforn et al, 1998; Argus et al, 1989; Kaabouben et al, 2008) and 17 October 1983 (Argus et al, 1989) Some of these earthquakes generated tsunamis, described in historical documents and recorded by tide stations, namely on 31 March 1761, November 1941 and May 1975 (Baptista et al, 2006; Kaabouben et al, 2008; Baptista and Miranda, 2009). The use of seismic and tsunami data provides a better understanding of this earthquake and tsunami
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