3D physics-based numerical modeling as a tool for seismic risk assessment of urban infrastructural systems: the case of Thessaloniki, Greece

The aim of this paper is to develop a seismic risk assessment study of urban infrastructural systems relying on state-of-the-art tools for the prediction of earthquake ground motion as well as the assessment of vulnerability. The proposed approach makes use, on one hand, of 3D physics-based numerical simulations of source-to-site wave propagation problems to provide an accurate description of spatial variability of ground shaking and, on the other hand, of systemic approaches for the evaluation of the vulnerability of complex, interconnected urban systems. The city of Thessaloniki, in Northern Greece, is taken as case study and the physical damage and loss of performance for the main water supply system are estimated based on connectivity based performance indicators. A couple of rupture scenarios with magnitude MW equal to 6.5 and 7.0, breaking two major hazardous faults around the city are used. The results indicated that 3D simulations can efficiently and accurately account for near-source conditions, geological and site conditions at local scale as well as for spatial and cross-correlation of ground motion. The risk estimates are compared with the ones obtained using a standard approach based on Ground Motion Prediction Equations (GMPEs), accounting for the spatial variability of ground motion. It was concluded that the GMPEs based approach can be used for a preliminary and faster seismic loss estimation. However, the results shed light on the main advantages of a full 3D numerical modeling for seismic risk assessment in large urban environments and spatially distributed systems. A major advantage is the more accurate estimation of spatial correlation of ground motion, which is location- and earthquake- specific.