Palaeoseismological investigation of the Tyrnavos Fault (Thessaly, Central Greece)

Abstract

A palaeoseismological investigation has been carried out along the Tyrnavos Fault, an ESE–WNW trending, north-dipping normal fault representing one of the major tectonic structures bordering the Late Pleistocene–Holocene Tyrnavos Basin, Northern Thessaly, Central Greece. According to geological, structural, morphotectonic and geophysical researches, the Tyrnavos Fault has been geometrically and kinematically characterised as a typical “Aegean-type” active fault. Six trenches have been excavated and logged in detail in order to quantify the most important seismotectonic parameters, like the characteristics of past earthquakes, their ages, the elapsed time from the last event, the short-term slip-rate and the mean return period. Several samples have been also collected for absolute dating that has been performed with different techniques like TL, OSL and AMS. Sedimentological, structural and chronological data document a Late Pleistocene to Holocene morphogenic activity of the Tyrnavos Fault, which is characterised by vertical co-seismic displacements of 20–40 cm and possible recurrence interval of 2–2.5 ka. The comparison between the estimated short-term (ca. 0.05–0.1 mm/a) and long-term (0.1–0.2 mm/a) slip-rates and the elapsed time from the last earthquake suggest the occurrence of a possible seismic gap along the Tyrnavos Fault. Due to the peculiar position of the selected site at the termination of the fault scarp in the bedrock, the lateral variability in morphogenic behaviour of an active fault is also observed. The location of the fault within a highly populated region and the proximity to the third largest town of Greece (Larissa) increases the seismic hazard of the area.