The 20 and 27 April 1894 (Locris, Central Greece) Earthquake Sources through Coeval Records on Macroseismic Effects

Newly retrieved coeval records on the effects of the two large earthquakes of 20 and 27 April 1894 in Locris (central Greece) have been analyzed to assess macroseismic intensities according to the European Macroseismic Scale (Grunthal, 1998). An intensity equal or higher than 8 has been estimated at 70 different places. The two earthquakes were close in time and both focused on the same area; this asked for an interpretation free, as much as possible, from the prejudice due to the accumulative descriptions implied, for instance, by the 1894 scientistsʹ reports. To image the earthquake sources and derive the main seismic parameters, we processed the macroseismic intensity data by using the Boxer method proposed by Gasperini et al. (1999). On the basis of this approach and our new sets of data, we obtain M 6.4 and 6.5 for the 20 and 27 April earthquakes, respectively, the latter being substantially smaller than the estimates proposed in previous works. Results obtained from the processing of macroseismic data have been tested and compared to recent geological data. Our preferred interpretation is that the 20 and 27 April 1894 earthquakes ruptured together the whole Atalanti fault. The internal structural complexity of the Atalanti fault appears to have controlled the rupture propagation: the change in strike of the fault trace along with its intersection with the Malesina fault, near Proskinas, is interpreted as a geometric barrier that is the boundary between the two individual earthquake sources. The 20 April earthquake would have ruptured between Proskinas and Skroponeri Mountain, southeast of the village of Larimna, whereas the 27 April earthquake ruptured between Proskinas and the northwest Chlomon fault zone, north of the town of Atalanti.