Large seafloor rupture caused by the 1956 Amorgos tsunamigenic earthquake, Greece

In the Mediterranean Sea, the probability that a large earthquake-triggered tsunami will occur in the coming decades is high. Historical tsunami databases document occurrences but the causative submarine faults are often unknown. Here we identify the submarine rupture of the 9 July 1956 Amorgos earthquake that generated the largest Mediterranean tsunami of the past two centuries. Using submarine vehicles, we explored major normal faults in the epicentral area and discovered a large surface rupture along the 75-km-long Amorgos fault. The 9.8–16.8 m seafloor offset is compatible with a Mw ~7.5 event. This finding prompts reassessment of the origin of the largest (≥20 m) tsunami waves, previously attributed to earthquake-triggered submarine mass wasting. It demonstrates that tsunami sources can be determined decades after an event, a key advance for assessing future seismic and tsunami hazards.