1d and 2d Linear and Nonlinear Site Response in the Grenoble Area

In this study we present 1D and 2D linear and nonlinear wave propagation simulations in the Grenoble basin up to 10 Hz. The numerical computations show that the strong impedance contrast between the sediments and surrounding bedrock produces a strong amplification regardless of the basin geometry. This velocity contrast also helps the development of strong surface waves at the basin edges. As a consequence, the amplification from the 2D case is higher than the 1D results. Nonlinear effects become important for an input acceleration of 0.2g and are responsible for a strong deamplification of the ground motion within the basin. Furthermore, the soil nonlinearity makes the ground motion in the basin to appear more coherent than the linear case. The computed transfer functions from nonlinear results show an evident deamplification between 1 and 5 Hz with respect to the linear ones. These results suggest that a 2D and 3D geometry should be taken into account for a more accurate estimation of the basin response.