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2D Numerical Investigation on the Effect of Random Velocity Perturbations on Seismic Ground Motion: Application to Site Effect Assessment in the Nice (France) Sedimentary Basin

It is well known that the characteristics of the shallow geology can affect the seismic wave propagation and may produce large ground motion amplifications during earthquakes. This is mainly due to their low velocity compared to the underlying bedrock. In sedimentary basins, their geometry can furthermore lead to seismic wave focusing, hence complexifying ground motion amplification. The assessment of these site effects is important for seismic hazard evaluation. Numerical simulations of seismic wave propagation can be used to understand and predict site amplification. The reliability of simulations depends on how the velocity model used reflects the reality. For long period or large-scale simulations, smooth velocity models are generally adequate. At short periods, where the effect of small-scale soil heterogeneities on seismic wave propagation can be important and their consideration becomes crucial. Due to the difficulty to map these heterogeneities, statistical methods are often used to model them. Using a detailed velocity model of the Nice (France) sedimentary basin, we performed 2-D numerical simulations of seismic wave propagation to investigate the effect of short-wavelength heterogeneities on surface ground motion. Velocity heterogeneities within the basin are modeled statistically as a stationary, homogeneous random process with a 2-D Von Karman autocorrelation function. We investigate how different parameters of this function affect ground motion in terms of peak ground velocity, pseudo-spectral acceleration and standard spectral ratios. We show that the presence of velocity heterogeneities increases ground motion variability and may increase or decrease the spectral amplification depending on the local configuration of the media’s statistical parameters.

Presenting Author: Flomin N. Tchawe

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