Passive seismic prospecting in Venice historical center for impedance contrast mapping

Extensive passive seismic prospecting has been conducted in the historical center of Venice (North Italy) aimed to map subsoil impedance contrast. Venice represents an emblematic study site of the challenging characteristics that can be encountered in historical sites, both stratigraphic and logistical, limiting the application of common microzonation techniques. A total of 82 single station passive HVSR acquisitions and passive surface wave arrays analysis have been performed to estimate the main impedance contrasts of the first subsoil, capable of interaction in terms of resonance with the monumental buildings. The results of the geophysical analysis have been integrated with available stratigraphic information derived from published researches and from hundreds of boreholes stored in an institutional database. The results have been then analyzed by means of a geostatistical approach based on cokriging interpolation, which permitted to map the impedance contrast beneath the ancient historical center. The adopted interpolation algorithm permitted to map the impedance contrast with an integrated use of existing information based on HVSR acquisitions and stratigraphic data. The map of impedance contrast is congruent with the literature geo-engineering evidences such as subsidence and geological reconstructions. The achieved results open new perspectives for the use and analysis of passive seismic techniques in challenging environments as historical urban centers characterized by high subsoil heterogeneity. Moreover, an improved knowledge of the shallow stratigraphy would permit to shed light on the complex interactions between anthropic activities and geoenvironmental processes, including climate change that characterized the long history of Venice.