Deterministic Seismic Hazard Assessment for Santorini from the 1650 Kοlumbo eruption seismicity: impact calibration using the 1956 Amorgos mainshock (M7.4) damage pattern

Abstract We employ a Deterministic Seismic Hazard Assessment (DSHA) approach to study the impact of seismicity associated with the 1650 Kolumbo volcano eruption within the Santorini island complex. For this reason, a stochastic simulation approach is used to compute synthetic seismic records and evaluate the spatial variation of strong ground motions within the study area. We calibrate the stochastic simulations by using the damage distribution of the Amorgos 1956 ( M ~7.5) mainshock, a major, normal faulting, regional tectonic event. The observed damage pattern for this earthquake revealed that the Santorini caldera topography amplifies ground motions by a factor of ~1.4–2.0. For this reason, we quantify the contribution of topographic effects by introducing a generic, frequency-dependent topographic amplification approach for horizontal seismic motions directly in the stochastic simulations. Site effects are taken into account by considering the two main geotechnical formations, which are typically met at the Santorini island complex. Using the proposed approach, we are not only able to model the 1956 damage distribution, but to also provide a realistic scenario for the 1650 damage pattern, assuming the occurrence of a M 6.5 mainshock along the Anydros fault, located close to the submarine Kolumbo volcano. The proposed systematic increase of the modeled macroseismic intensities along the Santorini caldera rim suggests that topographic phenomena should be readily introduced in seismic hazard assessments for the caldera settlements, especially of northern and central Santorini, where the majority of the permanent but also touristic population resides.