Simulation of off-fault surface effects from historical earthquakes: The case of the city of thessaloniki (northern greece)

Abstract

Thessaloniki, the second largest city in Greece, is located at the northeastern shore of Thermaikos Gulf, a shallow water body and remnant of the Axios valley sedimentary system that has received massive sedimentation. The broader region is surrounded by neotectonic fault zones, several of which can be considered as active, based on their kinematic data compatibility with the active stress field and the frequent microseismicity. Part of the city is built on basement rocks of primarily Mesozoic age, but most of it is founded on the sedimentary filling of the Axios basin that has been active since Eocene. Historical records indicate that Thessaloniki, has suffered several earthquake disasters, both from sources close to the city, as well as from more distant sources (e.g. 1829 M7 Drama and 1904 M7 Kresna events). The event of 1759 (MMI IX; M6.5) is reported as the most destructive for Thessaloniki with a postulated epicenter at the Axios River estuary in Thermaikos Gulf. We combine the most updated tectonic and seismological data for the broader Thessaloniki area to postulate a scenario of a moderate-magnitude earthquake and model the expected strong shaking and off-fault coseismic surface effects, with emphasis on liquefaction phenomena that match the damage patterns described in historical archives. In particular, we delineate zones prone to liquefaction occurrence and evaluate the potential of the geological units. The latter is achieved based on data provided by in situ tests and the former based on information provided by geological maps regarding the age and depositional process of the sediments.