Coulomb stress triggering of earthquakes along the Atalanti Fault, central Greece: Two April 1894 M6+ events and stress change patterns

Two M6+ events occurred 15–20 km apart in central Greece on April 20 and April 27, 1894. We identify the April 27, 1894 rupture (2nd in the sequence) with the Atalanti segment of the Atalanti Fault Zone because of unequivocal surface rupturing evidence reported by Skouphos [Skouphos, T., 1894. Die swei grossen Erdbeben in Lokris am 8/20 und 15/27 April 1894. Zeitschrift Ges. Erdkunde zu Berlin, vol. 24, pp. 409–474]. Coulomb stress transfer analysis and macroseismic evidence suggest that the April 20, 1894 event (1st in the sequence) may be associated with the Martinon segment of the same fault zone. Our stress modelling suggests that this segment may have ruptured in an M = 6.4 event producing a 15-km long rupture which transferred 1.14 bar in the epicentral area of the April 27th, 1894 event, thus triggering the second M = 6.6 earthquake along the Atalanti segment and producing a 19-km long rupture. We also examined three alternative fault sources for the first event; however, all these produce smaller stress stresses for triggering the second event. The proposed slip model for the second earthquake is capable of producing coastal subsidence of the order of centimetres to decimetres, which fits the geological data. The 1894 earthquake sequence was followed by a difference in the timing of subsequent M > 5 events in each of the “relaxed” areas (stress shadows; a negative change in Coulomb failure stress > − 0.6 bar), which terminated between 22–37 years (north) and 80 years (south).