Historical co-seismic uplift rates in the eastern Hellenic Subduction Zone: the case of Rhodes Island

In the eastern Hellenic Subduction Zone important coastal uplift occurred along the east coast of Rhodes Isl. (Greece) during the late Holocene, with uplift gradient increasing from south to north. Various authors estimated geologically that the mean uplift rate has been at similar to 1 mm a(-1) in the last similar to 6 ka and at the range 1.4-3.9 mm a(-1) in the last 33 ka. To estimate the rate of net, co-seismic costal uplift during the last similar to 2.3 ka we analyzed the historical earthquake and tsunami activity based on little-known documentary sources of the 2nd and 19th centuries, on recalculation of magnitudes for some of the earthquakes and eventually on the critical evaluation of the various seismic catalogues available. Published data regarding elevated shorelines, C-14 dating and tsunami sediment deposits have been taken into account too. We performed field observations to verify co-seismic uplift in elevated shorelines and in the ancient harbor of Rhodes. It was found that since the 3rd century BC co-seismic coastal uplift at NE Rhodes has been produced by four non-tsunamigenic earthquakes in similar to 227 BC, AD similar to 142, 1481 and 1856. The first three shallow earthquakes had their sources very likely close to NE Rhodes, while the 1856 event very likely was an intermediate-depth earthquake. Maximum uplift of similar to 3.8 m has been attributed alternatively to the 227 BC or to the AD 142 events but the uplift caused by the rest events has been of smaller amplitude. Due to the uncertainties involved in the timing and amplitude of uplift the estimated cumulative net uplift ranges from 5.75 m to 6.95 In, which returns uplift rate of 2.5-3.0 mm a(-1). This rate exceeds the late Holocene rate but is consistent with the long-term geological uplift rate. About half of the total seismic moment released by the four episodes was released by one major earthquake (M similar to 7.7) occurring either in 227 BC or in AD 142. Such a major event produced similar to 60% of the total net uplift. The rest amount of uplift, however, was contributed by smaller but still large (M >= 7.0) earthquakes. Coastal uplift contributed by either sediment underplating or aseismic slip is not evident at least during the late Holocene.