Publication Date:
2018-03-19
Description:
The tsunami catalogues of the Atlantic include two transatlantic tsunamis in the 18th century the extensively studied 1st November 1755, and 31st March 1761. The latest event struck Portugal, Spain, and Morocco around noontime. Several sources report a tsunami following the earthquake as far as Cornwall (United Kingdom), Cork (Ireland) and Barbados (Caribbean). An earlier analysis of macroseismic information and its compatibility with tsunami travel time information located the epicentre circa 34.5°N 13°W close to the Ampere Seamount at the eastern end of the Gloria Fault (North East Atlantic). The estimated magnitude of the earthquake is 8.5. In this study, we propose a tectonic source for the 31st March 1761 earthquake compatible with the tsunami observations in the Atlantic. We revisit the tsunami observations, reevaluate tsunami travel time data, and include a report from Cadiz not used before. The global plate kinematic model NUVEL 1A computes a convergence rate of 3.8mm/y in the area of the presumed epicentre. We propose a source mechanism for the parent earthquake compatible with the geodynamic constraints in the region capable of reproducing most of the tsunami observations. The results of our study support the hypothesis that the 1761 event took place in the area of Coral Patch and Ampere seamounts, SW of the 1st November 1755, mega-earthquake source. Finally, this study shows the need to include the 1761 event in all seismic and tsunami hazard assessments in the Atlantic Ocean.
Electronic ISSN:
2195-9269
Topics:
Geography
,
Geosciences
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