Comment caractériser les effets de site des structures complexes à partir du bruit sismique ambiant. Application au bassin de Santiago du Chili
Congress title :AFPS'07 7ème Colloque National
Congress town :Châtenay-Malabry
Congress date :04/07/2007
Microtremor techniques such as the H/V method and the more advanced array analysis have the potential to significantly contribute to effective seismic hazard mitigation. These methods, reliable in horizontal layering, may be misleading in the case of2D or 3D structures. This discrepancy is mainly due to the complexity of surface wave propagation in such media. Extensive ambient noise measurements were performed in the basin of Santiago de Chile (Chile). We look for testing the H/V technique and the array analysis as a tool to provide qualitative and quantitative information of sites affected by known 3D geometrical and geological features. Analysis of microtremor records led to separate H/V curves into three groups: (1) H/V shapes exhibiting clear peak(s), (2) H/V curves showing low amplitude broadpeak(s) or plateau-like shapes, and (3) flat H/V curves. In the case of clear H/V peaks, the reliability of the average shear wave velocity and sediment thickness compare well to available geological, geophysical and geotechnical data. In the two other cases, it is not possible to easily correlate with the available information. This suggests that H/V data should be carefully analyzed in complex media before generalizing and mapping soil thickness, velocity, and frequency.