Multiple submerged tidal notches: A sea-level indicator of sequences of coseismic subsidences in the Aegean region.

Citation:

Evelpidou N, Pirazzoli P. Multiple submerged tidal notches: A sea-level indicator of sequences of coseismic subsidences in the Aegean region. In: International Colloquium 'The Mediterranean Islands". Cargese, France; 2015.

Date Presented:

30/6-2/7

Abstract:

Tidal notches are a well-known sea-level indicator, marking clearly former shorelines, which have often been used to deduce Quaternary tectonic trends and sea-level changes, mainly in uplifting areas. If raised notches have often been used to estimate past changes in sea level and tectonic movements, submerged notches, which are more difficult to observe, have been studied mainly occasionally by a few authors. Nevertheless, Holocene tectonics may include more than a single episode and it may be useful to extend underwater observations below the first submerged notch. In this context, this work focuses in the Aegean region, an area characterized by extensional tectonics, where subsidence prevails, related to the subduction of the Mediterranean floor below the Hellenic arc, where Quaternary uplift trends tend to prevail. In some islands of Cyclades and Sporades, there is evidence of the occurrence of repeated rapid subsidences during the Late Holocene. In this paper, the shape of tidal notches that may well be preserved underwater is recalled in order to reconstruct sequences of coseismic subsidences and other relative sea-level changes that occurred during at least the last few millennia. A re-analysis of already published measurements of submerged tidal notches in several islands reveals that subsidence trends in many areas of the Aegean are not continuous and gradual, but the result of repeated coseismic vertical subsidences of some decimetres at each time. The estimated average return times are of the order of approximately some centuries to one millennium. Although the results cannot be used for short-term predictions of earthquakes, they may provide useful indications about the long-term tectonic trends that are active in the Aegean region.