Seismic hazard assessment in the area of Mystras-Sparta, south Peloponnesus, Greece, based on local seismotectonic, seismic, geologic information andon different models of rupture propagation

Strong seismic events once again confirm the view that great destructive ea rthquakes are produced by the reactivation of pre-existing faults although they have usually remained inactive for many, perhaps thousands of years. I t is evident that such active seismogenic zones, with little or no seismici ty, have presumably been ignored in the determination of the region's seism ic hazard. At south Peloponnesus, Greece, is situated at Taygetos mountain. At its eas tern front lies a large normal fault system, the southern segment being the Sparta fault. This area has been characterized by low seismicity for the l ast 25 centuries. However, during the 6th and 5th centuries B.C. several de structive earthquakes have been reported. That of 464 B.C., was the most de structive and devastated the city of Sparta. Detailed morphotectonic observ ations of this area, suggest that the earthquake of 464 B.C. could be relat ed to the most recent reactivation of this fault. The ground accelerations that would be produced by a future activation of t he Sparta fault, were calculated, by applying a method which takes into acc ount information mainly from the seismotectonic parameters of the Sparta fa ult, the rupture pattern, the properties of the propagation medium and the local ground conditions. Moreover, these results were compared with those o f other independent studies based mainly on the seismic data of the area. T his method estimated greater expected values of ground acceleration than th ose computed by the conventional seismic hazard methods. The highest values correspond to the activation of the Sparta fault either in a unilateral ru pture, which would start from the southernmost point of the fault, or in a circular one. Furthermore, an increase is observed of the order of 50% in t he ground acceleration values in unconsolidated soft ground in relation to the corresponding values of hard ground.