Structural and geotechnical engineers have been aware for a long time of soil-structure interaction (SSI) phenomena, which modify the seismic response of massive or tall buildings erected on soft soils. On their side, seismologists have known for a long time that it is not a good idea to install seismological stations close to trees. During the last decades, it has also become clear how large the effects of surface heterogeneities, commonly called 'site effects' (SE, concerning soft soils as well as topographic features), can be. On this basis, it is legitimate to wonder whether a large building on a soft soil can contaminate the ground motion in its immediate vicinity (phenomenon hereafter abbreviated as 'CGMB', Contamination of Ground Motion by Buildings). Going one step further, we may ask about the overall effect of such contamination in a densely urbanized area. The aim of this chapter is to present an overview of the results that substantiate the plausibility of this kind of 'global' interaction between all the buildings of a city and its subsoil, which we call hereafter 'site-city interaction' (SCI).
