Pergamon Phy. Chem. Earth (A), Vol. 24, No. 4. pp. 361-367, 1999 0 1999 Elsevier Science Ltd All rights reserved 1464- 1895/99/$ - see front matter PII: S1464-1895(99)00042-3 Late Holocene Coseismic Vertical Displacements and Tsunami Deposits Near Kynos, Gulf of Euboea, Central Greece P. A. Pirazzoli’, S. C. Stiros2, M. Arnold3, J. Labore14 and F. Laborel-Deguen4 ‘CNRS-UMR 8591, Laboratoire de Geographic Physique, 1 Place Aristide Briand, 92195 Meudon Cedex, France, email: pirazzol@cnrs-bellevue.fr 2Department of Civil Engineering, University of Patras, 26500 Patras, Greece 3CNRS-CEA, Centre des Faibles Radioactivites, TANDETRON, Avenue de la Terrasse, BPl, 91198 Gif-sur-Yvette, France 4Chemin des Grands Bassins, 13600 La Ciotat, France Received 24 April 1998; accepted 20 October 1998 Abstract. Marine bioerosion marks and radiocarbon AMS dating give evidence of a two-phase sequence of coseismic vertical displacements which occurred during the Late Holocene in the Livanates-Arkitsa area (south coast of the Euboea Gulf). Morphological and biological arguments suggest that both the displacements were superimposed on a gradual relative sea-level rise. The earlier coseismic movement (a subsidence of 0.9 m max.) is possibly related to a tsunami wave, dated between 1380 and 965 B.C., which swept at 16 m in altitude the nearby archaeological site of Homeric Kynos. The later coseismic movement, between 360 B.C. and A.D. 210, was an uplift greater than 1.4 m. 0 1999 Elsevier Science Ltd. All rights reserved. 1 Introduction Located in one of the most active seismic regions of Greece, the Gulf of Euboea is known to have experienced several violent earthquakes during historical times, some of which accompanied by devastating tsunami waves (Guidoboni et al., 1994). The general tectonic structure of the region has been discussed by Roberts and Jackson (199 1) (Fig. l).The main tectonic feature in this area is the Locris (Atalandi) normal fault zone, for which coseismic subsidence movements have been documented at the time of earthqnakes in 426 B.C. and in A.D. 1894 (Stiros and Rondogisnni, 1985). A few kilometres north of the Locris fault, evidence of uplift movements (Lithophuga borings) can be found in the coastal area between Livanates and Arkitsa (Roberts, 1988; Roberts and Jackson, 1991). The present note is based on field observations made in this uplifted coastal ares and especially on the analysis and AMS 14C dating of marine samples collected near Kynos (38’44’ N, 23’04’ E). Correspondence to: P.A. Pirazzoli 2 Methods Emerged occurrences of shells of the Mediterranean date mussel Lithophagu lithophugu (L.), still articulated inside their burrows, can be used to identify former shoreline positions and even to demonstrate, under certain conditions, that their uplift was very rapid (coseismic), because if elevation was slow (millimetres per year or centimetres par year) the shells would be altered and destroyed in a few years by mid-littoral bioerosion (Stiros et al., 1992; Laborel and Laborel-Deguen, 1994). In the field, elevation of emerged fossil Lithophugu samples was measnred by reference to the upper limit of present-day live counterpart (with an accnracy of f 0.1 m) and considered to indicate minimum emergence. This procedure eliminates tmcertainties derived from the estimation of sea-level changes of tidal (local tidal range can be estimated at about 0.4 m) and meteorological origin. For each shell sample to be dated, a fragment of ca. 100 mg of shell was isolated from the surrotmdig material and firstly cleaned mechanically by blasting with alumina powder in order to remove possible contamination by Fig. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLK 1. Location map. zyxwvutsrqponmlkjihgfedcbaZYXWVU Major range.-hounding faults are shown in heavy lines with zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONML ticks on their dcamthmwn side. 361