Bulletin of the Seismological Society of America, 96(5), pp.1934-1951, 2006 1 Seismic Site-City Interaction: Main Governing Phenomena Through Simplified Numerical Models By Marc Kham*, Jean-François Semblat*

Abstract. This work focuses on the analysis of the multiple interactions between soil layers and civil engineering structures in dense urban areas submitted to a seismic wave. To investigate such phenomena, called Site-City Interaction (SCI) herein, two simplified site-city configurations are considered: a homogeneous, periodically spaced city and a heterogeneous, non-periodically spaced city, both on a constant depth basin model. These 2D BEM models are subjected to a vertically incident plane SH Ricker wavelet. A parametric study of the city parameters (density of buildings and their natural frequencies) and the thickness of the basin is carried out to characterize the SCI, and to investigate its sensitivity to some governing parameters. The following parameters are analysed: building vibrations, induced ground motion, ground motion perturbations inside and outside the city, spatial coherency and kinetic energy of the “urban wavefield”. It results that a so-called “site-city resonance ” is reached when the soil fundamental frequency and structures eigenfrequencies coincide; building vibrations and ground motion are then significantly decreased and the spatial coherency of the urban field is also strongly modified. Building density and city configuration play a crucial role in the energy distribution inside the city.