Revisiting the Peloponnese Western Hellenic Arc earthquakes of August 30th, 1926 and July 1st, 1927

Abstract

Two earthquakes from the first half of the twentieth century in the Peloponnese region (southern Greece) are analyzed here. These earthquakes occurred 1 year apart in the summers of 1926 and 1927; epicentral locations in the literature show them close to each other (~ 50 km apart). The earthquakes are of particular importance for at least two reasons: they appear to be of intermediate depth and macroseismic data associated with them has been available until now in paper format. Intermediate depth earthquakes are associated with the subduction zone along the Hellenic arc and do not occur as frequently as crustal earthquakes, therefore making the revisiting of such events even more important. Historical European databases which hold macroseismic data, such as AHEAD ((Albini et al. Istituto Nazionale Di Geofisica e Vulcanologia (INGV), 2013), are essential for disseminating this data type and making the different studies for each seismic event in the catalogue available. However, AHEAD includes earthquakes that occurred prior to 1900. Paradoxically, it is easier to find the macroseismic field of an earthquake from the 1500s than one from the early twentieth century. Therefore, disseminating and analyzing the macroseismic data of the two Peloponnese events from this period, previously available only in paper format, is crucial. In line with this goal, newly collected eyewitness accounts with existing observations for these events are presented, while macroseismic intensities are re-assigned in EMS98. Re-estimated epicentres suggest that the 1926 earthquake occurred further offshore, while the 1927 earthquake was on land at the southernmost tip of the Peloponnese peninsula. Isoseismal maps were created for both events using the Rossi-Forel and EMS98 scales. The use of modern unified European macroseismic scale (EMS98) in the study of historical earthquakes is essential for harmonizing the present and past with future hazard and risk analyses. The use of EMS98 with additional IDPs in the construction of isoseismal maps further refines the macroseismic field of the 2 events, while suggesting a different fault rupture orientation.