Segment boundaries, the 1894 ruptures and strain patterns along the Atalanti Fault, Central Greece

Abstract

The Atalanti Fault is a large active normal fault segment inside the Gulf of Evia Rift system (Central Greece), that last ruptured during the April 1894 earthquake sequence. Using structural and geomorphological interpretations of digitally processed Landsat TM satellite imagery, two regions of i) low topography, ii) minimum hinterland development and iii) transverse bedrock ridge development, 34 kilometres apart were identified; these regions are suggested to be segment boundaries constraining the length of the fault. From throw profiles and displaced syn-rift strata, we estimate a minimum slip of 810m at the central region of the fault (Tragana), increasing to a value of 1200 meters within the Asprorema embayment area. These figures averaged over a time span of 3 million years (age of oldest offset syn-rift), yield mean slip rates of at least 0.27 to 0.4 mm/year. Field studies were also conducted along the length of the Atalanti Fault Segment to reexamine and map the 1894 ruptures. The surface break is only preserved locally where the footwall comprises a resistant bedrock lithology (limestone), whilst the rest of the rupture noted in historical records propagated along the contact with the volcanic pre-rift, as well as within the syn-rift, and has since been eradicated due to man-made changes in surface morphology. The surface breaks appear not to have crossed over the segment boundaries that we propose, but seem to have ruptured the full length of the Atalanti Fault Segment, that is, 34km. These observations suggest that the 1894 rupture is the longest mapped within Central Greece. However, it remains unclear whether the ruptures were produced solely by the 27/4/1894 earthquake, or by two events, one week apart. We discuss the implications for fault-behavioural models and seismic hazards for the Atalanti area.