Coastal wetlands as recorders of earthquake subsidence in the Aegean: a case study of the 1894 Gulf of Atalanti earthquakes, central Greece

Earthquakes may have a major impact on the morphology and evolution of coas ts in tectonically active areas, In the area of the Gulf of Atalanti, centr al Greece, a damaging earthquake sequence in 1894 is reported to have cause d nearshore slumping, tsunami-induced flooding, and decimetre-to metre-scal e coastal subsidence, The earthquakes caused major changes to coastal confi guration, in particular the separation of the Gaiduronisi peninsula from th e mainland, Detailed stratigraphical, microfossil and radiometric (Pb-210 a nd Cs-137) analyses of coastal wetlands around the Gulf of Atalanti show th at these environments preserve evidence of sudden, lasting subsidence conte mporaneous with the 1894 events, with foraminiferal assemblages at a site o n the mainland opposite the island indicating an abrupt change from suprati dal soil to intertidal marine conditions. The elevation change indicated by this terrestrial to marine transition is 30-80 cm, The coastal stratigraph y in the Atalanti area however lacks laterally extensive sharp soil-mud con tacts or tsunami deposits of the type used in identifying past earthquake s ubsidence events at plate-boundary settings. Despite the major earthquake-i nduced changes in coastal configuration, the stratigraphical signature of t he 1894 earthquakes is relatively subtle, and is consequently difficult to distinguish from other rapid coastal changes (e,g, storm events or barrier breaching) without high-resolution dating control and reference to document ary records. For this reason, coastal wetland stratigraphies are only likel y to be useful in identifying prehistorical or poorly documented earthquake s in the Aegean at sites where metre-scale coseismic elevation changes and/ or major tsunami inundation have occurred. In addition, the resolution of t he biostratigraphic data reported here is insufficient to distinguish betwe en the contrasting fault rupture models for the 1894 events. The coastal el evation changes recorded in these wetlands, however, are best accounted for by a slip of Im on a multi-segment fault. (C) 2000 Elsevier Science B.V. A ll rights reserved.