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Abstract

Site response analysis is essential for evaluating seismic hazard and risk assessment and for providing useful data for land use planning. However, current regional site amplification models do not have the necessary resolution for sites such as alpine valleys, where site response is characterized by complex effects. In this study, the site response of the lower Sarca Valley (northern Italy) was first evaluated at a limited number of sites corresponding to the locations of earthquake recordings. Then, the site response (in terms of spectral amplification curves and duration lengthening) was spatially extended where recordings of earthquakes were not available, by the application of cluster and a correlation analysis, using the noise NHV recorded throughout the valley by single-station noise measurements. In this way, could finally zonate the area into three parts with different site response characteristics: the area where the bedrock outcrops, characterized by a flat response; an area around the valley axis where the sediments reach a thickness of about 450 meters, characterized by high amplification values (up to 10) and ground motion lengthening of several tens of seconds at frequencies below 1 Hz; an area at the valley margins where the sediments become thinner, characterized by spectral amplification at frequencies between 1 and 10 Hz. The results obtained can provide useful information for hazard and risk scenarios and for improving lower resolution regional maps at the local scale.