East Taygetos Fault Zone (Peloponnesus, Southern Greece): Dormant fault zone bordering awake neotectonic structure

The eastern flank of Taÿgetos Mountain (southern Peloponnesus) is bordered by a normal fault zone striking NNW-SSW from Megalopolis basin to Lakonikos gulf near Gythio town, with a total length of about 80 km. A segment of this fault zone forms an impressive morphotectonic feature that is known as Sparta fault and it is located between Sparta town and Potamia village. The total length of this segment is about 20 km. Though this fault zone seems to be active since Pliocene, its present seismicity appears to be very low and sparse.
   In order to assess the geometrical parameters of this fault zone, a morpho-structural analysis was carried out using combinations of Landsat ETM+ panchromatic and multispectral images (bands 1, 3, 4, 5 & 7) filtered with edge enhancement 3x3, the geological maps covering the area from Megalopolis basin to Lakonikos gulf and the Global Elevation Model (GDEM) derived from Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) imagery. The GDEM has a nominal 30 meter cell size, but its effective spatial resolution is estimated between 100 and 120 meters. All these data were integrated in a GIS environment using the Greek coordinate system EGSA 1987.
   The kinematic analysis based on field observations shows the following multiple reactivations with a dip-slip movement of the entire fault zone since Pliocene: 1) an E-W extension during upper Pliocene 2) a NE-SW extension during lower Pleistocene and 3) a NW-SE extension during middle Pleistocene to the present. Assessment of the seismicity associated with this fault zone and the seismic potential based on its geometric and kinematic characteristics shows that it is a seismically dormant fault zone segmented into at least 3 segments of a length of about 20-25 km.
   The strong earthquakes of VI and V century BC which struck Sparta town seem to be associated with the central segment of the zone known as Sparta fault. Based on morphostructural analysis, the average slip rate since Early Quaternary could be estimated as 0.5 mm/yr, which allows us to characterize the fault as of moderate activity. Mmax for the fault of 20 km length could be estimated as M=6.5 and the corresponding Recurrence Time as 2,000 years average.
   The results of the estimated fault potential (Mmax, RT) using calculations of slip-rate model (slip rate 0.5 mm/yr) and EZ-FRISK software (Risk Engineering, 2005) fit to the parameters derived from empirical relations.
   The great destruction that Sparta town suffered at 550 B.C. and 464 B.C. could be attributed to high values of acceleration due to the close proximity to seismogenic fault (near field effect) as well as to the amplification of the strong ground motion due to loose quaternary deposits lying under Sparta town.