Quantification of modification of ground motion due to urbanization in a 3D basin using viscoelastic finite-difference modelling

This paper presents the quantification of modification of ground motion due to urbanization in a 3D basin as compared to the free-field motion. The complex interaction effects of basin and city on the ground motion during an earthquake are termed as site–city interaction (SCI) effect in this paper. The cities were developed using 3D building blocks of sixteen-storey (city 1) and eight-storey (city 2) buildings. The analysis, in terms of ground motion perturbation and % reduction in average spectral amplification (ASA) and kinetic energy (KE) as compared to free-field motion, of the simulated responses of the various 3D basin-city models revealed very large role of basin shape, sediment layering, city shape, building type in the city and city density in the SCI effects on the free-field motion. The first spectral amplification peak frequency at the top of the buildings corroborates with the combined fundamental frequency of the building block and sediment deposit in basin. The obtained very large amplification of the order of 49 at the top of a single B8 building may be due to the closeness of the fundamental frequency of the combined basin-building system with the fundamental frequency of the basin and the dominant frequency in the input signal. This was also responsible for the larger % reduction in ASA and KE in city 2 (B8 buildings) as compared to the city 1 (B16 buildings). Based on the analysis of the obtained results, it is concluded that if a city is developed considering into account the building type, city shape and city density as per the basin shape and sediment parameters can be highly beneficial in reducing the earthquake disaster.