Impact on built and natural environment of the strong earthquakes of April 23, 1933, and July 20, 2017, in the southeast Aegean Sea, eastern Mediterranean

Abstract

The southeastern Aegean Sea is one of the most active areas in eastern Mediterranean. On July 20, 2017, the area was inflicted by a strong earthquake (Mw6.6) causing damage mainly in Kos Isl., Greece. Kos was also struck by a lethal earthquake (~ Mw6.5) on April 23, 1933, the impact of which, however, remains little known. For better understanding the seismic hazard and risk in the area we assessed the impact on the built and natural environment caused by the two earthquakes. As regards the 1933 event we collected and evaluated documentary sources unknown so far in the seismological literature. The impact of the 2017 earthquake was evaluated from observational data collected during post-event field surveys in Kos Isl. We found that the 1933 seismic intensities assigned to various localities of Kos Isl. in MM and EMS-98 scales are systematically higher with respect to the intensities due to the 2017 earthquake. This result resembles the different levels of mortality caused by the two events: death toll of 181 in 1933 against 2 in 2017. These differences are likely interpreted by the higher physical vulnerability of buildings in 1933 with respect to 2017. However, the possible role of different location, source parameters and faulting processes between the two events should not be ruled out. The influence of such factors may possibly explain that the 2017 earthquake caused important environmental effects (soil liquefaction, tsunami) contrary to the 1933 earthquake which caused only minor ground failures while at all evidence did not triggered tsunami wave.