A reappraisal of the 1894 Atalanti earthquake surface ruptures, central Greece

This article presents the results of new field and aerial photo surveys of the Atalanti fault and of the mesoseismal area of the 20 and 27 April 1894 earthquakes. Coupled with a reanalysis of contemporary reports and previous investigations, these are used to gain a better understanding of the fault s responsible for these events and their seismic behavior. The first shock was smaller and probably located inshore or offshore the Malessina peninsul a. No resolving field evidence has been found to locate the seismogenic str ucture responsible for this shock. On the basis of the limited information available, we suggest the Malessina escarpment, a 12-km long, ENE-trending, NW-dipping fault as a possible structure responsible for this event. On th e other hand, the second and largest shock is definitely related to the Ata lanti fault sensu stricto, a main WNW-trending, N-dipping active fault exte nding between the Platirema valley (a few km NW of the town of Atalanti) an d Larymna. The total length of the rupture recognized in the field is about 32 km, but it can be extended further SE up to 40 km. No evidence for a lo nger rupture extending some other 20 km to the NW, between the Karagiozis r iver and Ag. Kostantinos, is found. The complex geometry of the fault with bends and step overs appears to be controlled by preexisting transverse str uctures. Minimum coseismic vertical throws, measured in the field after mor e than a century elapsed from the earthquake, are 30-80 cm, thus consistent with contemporary reports indicating 1-m average. Slip rates are not well constrained. The available estimates fall in the range 0.1-0.5 mm/yr confir ming the smaller amount of crustal extension taking place in this area with respect to other nearby regions such as the Corinth gulf. No new data are available to define the average recurrence interval typical of the Atalanti fault. However, a reconsideration of the existing information induced us t o rule out the possibility that the famous 426 B.C. earthquake occurred on the Atalanti fault. On the basis of the extent and size of the rupture reco gnized in the field, a M 6.8 is estimated for the second and largest shock.