The response of the Ubaye Valley (France) for incident SH and SV waves: Comparison between measurements and modeling

l> This paper presents a detailed study of the response of an alluvial valley in the Alps (France). The structure (Ubaye Valley) was chosen 1) for its moderate dimensions (500 m wide and 65 m thick), which allow an accu rate determina- tion of the deposit characteristics, and 2) for the relatively high seismicity of the region. The study included the deployment of five temporary seismological stations, a seismic survey of the valley for determining the dynamic proper1ies and the geometry of the soft deposits, and 1 D and 2D numerical modeling for incident SH and SV waves. Comparisons between observed and computed amplifications show a good agreement for frequencies lower than 10Hz and the particular direction of arrivai of the input motions corresponding to the 2D case. When the ear1h- quake sources are not located in the continuation of the line of seismometers, the spectral ratios exhibit a great variability between different groups of similar events. These observations indicate the azimuthal dependence of the site response and the need for 3D modeling.