HR: 1340h
AN: S53B-1275    [Abstracts]
TI: Multiple scattering of waves in random media: Application to the study of the city-site effect in Mexico City area.
AU: * Ishizawa, O A
EM: oai@andrew.cmu.edu
AF: LMSS-Mat, Ecole Centrale Paris, Grande Voie des Vignes, Chatenay-Malabry, 92295, France
AU: * Ishizawa, O A
EM: oai@andrew.cmu.edu
AF: (now at) Computational Seismology Laboratory, Civil and Environmental Engineering Department, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, United States
AU: Clouteau, D
EM: didier.clouteau@ecp.fr
AF: LMSS-Mat, Ecole Centrale Paris, Grande Voie des Vignes, Chatenay-Malabry, 92295, France
AB: Long-duration, amplifications and spatial response's variability of the seismic records registered in Mexico City during the September 1985 earthquake cannot only be explained by the soil velocity model. We will try to explain these phenomena by studying the extent of the effect of buildings' diffracted wave fields during an earthquake. The main question is whether the presence of a large number of buildings can significantly modify the seismic wave field. We are interested in the interaction between the incident wave field propagating in a stratified half- space and a large number of structures at the free surface, i.e., the coupled city-site effect. We study and characterize the seismic wave propagation regimes in a city using the theory of wave propagation in random media. In the coupled city-site system, the buildings are modeled as resonant scatterers uniformly distributed at the surface of a deterministic, horizontally layered elastic half-space representing the soil. Based on the mean-field and the field correlation equations, we build a theoretical model which takes into account the multiple scattering of seismic waves and allows us to describe the coupled city-site system behavior in a simple and rapid way. The results obtained for the configurationally averaged field quantities are validated by means of 3D results for the seismic response of a deterministic model. The numerical simulations of this model are computed with MISS3D code based on classical Soil-Structure Interaction techniques and on a variational coupling between Boundary Integral Equations for a layered soil and a modal Finite Element approach for the buildings. This work proposes a detailed numerical and a theoretical analysis of the city-site interaction (CSI) in Mexico City area. The principal parameters in the study of the CSI are the buildings resonant frequency distribution, the soil characteristics of the site, the urban density and position of the buildings in the city, as well as the type of incident wave. The main results of the theoretical and numerical models allow us to characterize the seismic movement in urban areas.
DE: 7212 Earthquake ground motions and engineering seismology
DE: 7290 Computational seismology
SC: Seismology [S]
MN: 2007 Fall Meeting