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The Helike fault is the most prominent fault appearing to control the westernmost sector of the Gulf of Corinth. It is divided into two segments (Fig. 8.1) (Koukouvelas et al 2001). The most western fault segment controls a 500m thick sedimentary basin and appears to be less active in terms of stream incision and freshness of the fault scarp. The easternmost fault segment has a total length 26km (22km onshore and 4km offshore). In 1861 the area suffered a severe earthquake that ruptured the eastern Helike fault for about a distance of 13km and caused a vertical displacement up to 1m. (Fig.8.1 and 8.2) This segment juxtaposes Quaternary fan deltas for more than 400m and controls the Kerynites river course in the alluvial fan, which occupies the hangingwall block. (Fig. 8.3a, 8.3b and 8.4) (Pavlides et al 2004)
Seven trenches excavated across this segment shows that the eastern Helike fault segment was activated three times during the last 2000 years, includingthat of the 1861 event. The other two identified events caused a vertical displacement of 1.37m and 0.44m, respectively. Their magnitude was estimated at 6,8 R and 6,7R and most probably occurred sometime between 190BC and 110 AD the former, and around 600AD the latter. The slip rate on the fault over the past 2000 years is estimated at about 1.5mm/year while the extension is about 1mm/year. These rates combined with the strain relaxation produced by the Aigio fault suggest that these two faults accommodate about 10% of the present day extension in the area. (Koukouvelas et al 2001).
Fig. 8.1: Map showing the Helike and Egion faults and the surface ruptures (Modified from Koukouvelas et al 2001) associated with the 1861 Eliki.
Fig. 8.2: Oblique aerial view of the Helike Fault segments, the step-over zone between the two segments and the course of the Kerynites River (KE). SEL: Selinous, VOU: Vouraikos. The dark grey circle represents the area of archaeological excavations. Photo courtesy the Helike Project. (From Koukouvelas et al )
Fig. 8.3a: Photograph showing part of the surface rupture associated with the 1861 Eliki earthquake. Grey arrows highlight the trace of the rupture (for location see Fig. 1) Width of photo 100m. From Koukouvelas et al 2001.
Fig. 8.3b: Recent photograph showing part of the surface rupture associated with the 1861 Eliki earthquake (Locality is shown in Fig. 1). Black arrows denote the fault trace and white arrows active landslides, for locations see Fig. 2. Width of photo is 200m. (From Pavlides et al 2004)
Fig. 8.4: Photomosaic showing the east end of the West Eliki Fault segment, the Eliki step-over zone and the East Eliki Fault. The Kerinitis courses are also marked through the last 2000 years or so. (From Pavlides et al 2004)
Koukouvalas, I., Stamatopoulos, L., Katsonopoulou, D. and Pavlides S. 2001. A pa laeoseismological and geoarchaeological investigation of the Eliki fault, Gulf of Corinth, Greece, J. of Structural Geol. 23:531-543
Pavlides, S., Koukouvalas J., Kokkalas S., Stamatopoulos L., Keramydas D., Tsodoulos J. 2004. Late Holocene evolution of the east Eliki Fault, Gulf of Corinth, (central Greece). Quaternary Int. 115/116:139-154