Palaeotsunamis and tsunami hazards in the Eastern Mediterranean

The dominant uncertainties in assessing tsunami hazard in the Eastern Mediterranean are attached to the location of the sources. Reliable historical reports exist for five tsunamis associated with earthquakes at the Hellenic plate boundary, including two that caused widespread devastation. Because most of the relative motion across this boundary is aseismic, however, the modern record of seismicity provides little or no information about the faults that are likely to generate such earthquakes. Independent geological and geophysical observations of two large historical to prehistorical earthquakes, in Crete and Rhodes, lead to a coherent framework in which large to great earthquakes occurred not on the subduction boundary, but on reverse faults within the overlying crust. We apply this framework to the less complete evidence from the remainder of the Hellenic plate boundary zone, identifying candidate sources for future tsunamigenic earthquakes. Each such source poses a significant hazard to the North African coast of the Eastern Mediterranean. Because modern rates of seismicity are irrelevant to slip on the tsunamigenic faults, and because historical and geological data are too sparse, there is no reliable basis for a probabilistic assessment of this hazard, and a precautionary approach seems advisable.