The Samos Mw6.9 event: Damage investigation in the town of Vathy incorporating a stochastic finite-fault source with site and structural information

The stochastic method is applied for the finite-fault modelling of strong ground motion from the October 30, 2020, shallow earthquake of Mw=6.9 which occurred offshore the northern part of Samos island in the Aegean Sea, Greece. The earthquake resulted to several human casualties and many injuries, to considerable infrastructure damage in Samos island and Western Turkey, especially in the city of Izmir, and a tsunami affecting both the Greek and Turkish coast. We focus this research on reproducing the ground motion field and damage pattern observed in Vathy, the capital of Samos Island. Different source representations, based on preliminary finite-fault slip distribution models, are tested against their capability to reproduce the two acceleration records available in Vathy. Site effects are incorporated in our modelling in the form of empirical amplification factors assigned according to a Vs30 distribution for the Samos island, which we constructed based on local geology and terrain-based proxies and on the Vs profiles at the sites of the two permanent accelerometric stations. The analysis further focuses on the empirical assessment of structural vulnerability for an estimated exposure model per building block in Vathy, which suffered structural damage due to the mainshock, mainly to a number of old and monumental buildings. The estimated exposure model in Vathy, when combined with the synthetic ground motion derived from the validated stochastic model, provides results in good agreement with available macroseismic intensities and damage reports. Our results contribute to better understanding the observed spatial distribution of damage in Vathy with respect to variations in the quality of buildings, the foundation soil and the frequency content of the excitation motion as radiated from the seismic source. The usefulness of our validated stochastic model is further demonstrated through blind predictions at sites of considerable earthquake effects, at which no record of the Mw=6.9 earthquake is available, such as in the town of Karlovasi in Samos and in the port of Chios Island.