Toward Seismic Microzonation—2‐D Modeling and Ambient Seismic Noise Measurements: The Case of an Embanked, Deep Alpine Valley

In the Sion area of Switzerland, part of a deep, embanked sediment‐filled valley, investigations on soil site effects have been conducted using two independent methods. Two‐dimensional (2‐D) modeling was performed with a program based on the Indirect Boundary Element Method (Pedersen et. al. 1994). Numerical simulations allow taking into account the subsurface geometry of the valley and its peculiar characteristics, such as a variable shape ratio and a high shear‐wave velocity contrast. The H/V method has been applied on ambient seismic noise measurements recorded on sites as close as possible to the 2‐D modeling. This technique allows capturing the fundamental resonant frequency of the deepest sediments as well as identifying the existence of a surficial deposit. Both approaches agree on the fact that the fundamental resonant frequency of the valley is below 1 Hz. The amplification level of the predominant frequency obtained with numerical simulation is up to two times higher than the one given by the H/V ratio. These results provide the basis for further investigations in order to resolve differences.