A Multi Scale Approach for the Ground Motion Modelling in Urban Areas

Seismic ground motion in urban environment is generally modified by the presence of build-ings. This phenomenon, referred to as Site-City Interaction, is mainly due to the radiated waves emitted through the soil by vibrating structures. Therefore, the urban seismic wavefield is al-tered from the free field motion with zones of higher and lower energy, i.e. largest and smaller ground motion amplitude, respectively. Because of the complexity of the phenomenon, model-ling and simulations of large dense cities might be performed with large computational costs. In this paper, a random urban wavefield is obtained through a hierarchical multi-scale ap-proach that defines representative areas obtained by homogenization of cluster of buildings at local-scale. An equivalent single oscillator is hence derived for each representative areas by considering uncertain parameters such as the fundamental period. Therefore, a proposed model combining discrete model and wave propagation model is used to evaluate the interac-tions among the several representative areas at city-scale to derive the seismic ground motion map for urban areas in terms of 50% fractile peak acceleration. Monte Carlo Simulation study is performed for validation purposes. Finally, the proposed framework is applied to a real ur-ban area using data from LIDAR maps