Inference of a seismic gap from geological data: Thessaly ( Central Greece) as a case study

Abstract

As a result of neotectonic, morphotectonic and seismotectonic research it is now possible to draw detailed maps of the major active faults affecting Thessaly, a large region of continental Greece. For many of these faults, where specific studies have been carried out, the degree of fault activity (i.e. the long-term slip-rate) has been also assigned ranging from 0.05 to 4 mm/yr-l. In the present work, the main morphotectonic features and seismotectonic characteristics of the more important faults are recalled from previous works, while the recent tectonic activity is compared with the seismic activity of the area. The occuuence of both large (M ?x2264; 6.0) and moderate (M ?x2265; 6.0) earthquakes during the present century is concentrated in the southern sector. Earthquakes have been virtually absent in the northern part of the region during the same period. In contrast, according to geological and geomorphological criteria, the recent (Late Quaternary) tectonic evolution of the region and the overall extensional rate do not seem to djffer significantly in the two sectors. Although palaeosejsmological trenches, geodetic surveying and the record of the microseismic activity may enhance our knowledge of this problem, on the basis of available geological (structural and morphological) data, it is likely that the northern sector of Thessaly represents a large seismic gap. The implications on seismic hazard in one of the more populated regions of Greece are also discussed.