Paleoseismological Trenching across the Atalanti Fault (Central Greece): Evidence for the Ancestors of the 1894 Earthquake during the Middle Ages and Roman Times

Abstract

The Atalanti fault bounds to the southwest the Evoikos Gulf, one of the major extensional basins of central Greece. This fault ruptured during the 1894 earthquakes, producing at the surface a complex, ca. 30-km-long rupture. Paleoseismological trenching performed at three sites along this fault provided the first insights on its seismogenic behavior. Unfavorable trench stratigraphy and scarcity of datable material made the identification and characterization of individual paleoearthquakes quite difficult. However, by integrating paleoseismological, geological, historical, and archaeoseismological data, we defined three surface-faulting earthquakes. The most recent event is the 1894 earthquake; the penultimate occurred during the Middle Ages between A.D. 770 and 1160, whereas the third event back occurred in Roman times between 50 B.C. and A.D. 230 and is interpreted to be the Opus earthquake of A.D. 105. These results suggest that 1894-type earthquakes repeat each 660–1120 yr. The average minimum slip per event and vertical slip rates are of the order of 45 cm and 0.4–1.6 mm/yr, respectively. These values are in agreement with other geological estimates and with geodetic measurements. Because of the short time elapsed since the 1894 earthquake, the Atalanti fault does not appear to contain an important seismogenic potential. On the other hand, these results may shed light on the potential of other seismogenic sources threatening the area.