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A rational evaluation of the seismic risk of urban areas cannot neglect the variability of the ground motion due to site amplification and the induced effects, such as soil liquefaction and slope stability. In this framework, the microzonation maps certainly represent the most adequate tool to account for this element in the seismic risk and for planning mitigation strategies. This study shows the preliminary results of a multidisciplinary research, which deals with the seismic microzonation of the Western area of Napoli. The selected case study is a challenging choice, as the seismic hazard is affected by both tectonic and volcanic seismicity, which in historical time differently affected the urban setting. The latter, in turn, results highly heterogeneous, as consisting of a mixing of both masonry and concrete structures. The adopted approach followed the recommendations of both the National and International Guidelines, with reference to the multi-levels methods. The collection, homogenization and synthesis of a significant number of existing data permitted the development of reliable geological and geotechnical subsoil models, leading to Grade I and II seismic microzonation maps, characterized by different expected amplification of ground motion and instability due to the liquefaction. Such maps represent a key for a quantitative assessment of seismic performance of buildings and infrastructures, in view of the expected urban requalification of the area.

The paper describes two recent examples of application of Electrical Resistivity (ERT) and Ground Penetrating Radar (GPR), for reconstructing buried subsoil and structural geometries in two historical sites in the city of Napoli. Both investigation sites were characterized by complex environmental and logistic conditions. The first case study was an ancient hypogean cavity excavated in the tuff, where the integration between ERT and GPR allowed to identify the depth of the soft rock below the natural and anthropic filling. The second investigation was finalized to detect the foundation geometry of a high monumental bell tower resting on loose alluvial and pyroclastic soils. In both cases, the joint interpretation of ERT and GPR tests confirmed the preliminary knowledge on the subsoil and addressed further direct investigation aimed at the stability and safety of the historical sites.

During the Abruzzo earthquake (6.IV.2009, MW = 6.3), the village of Castelnuovo, lying on an elliptical hill about 60 m high, underwent an intensive damage (IMCS = 9–10), that could be partly ascribed to the topographic amplification and to the presence of an underground cavity network. To verify these hypotheses, the seismic response of the hill was carefully investigated adopting both 2D and 3D finite difference numerical models. Analyses were carried out using a detailed geotechnical model, defined on the basis of a comprehensive field investigation (boreholes, DH, HVSR, ERT) and accurate laboratory tests (RC-TS). The reference input motion was reproduced considering the time history of the mainshock recorded at an accelerometric station close to the epicenter, conveniently deconvoluted to the bedrock and scaled in amplitude to the site of Castelnuovo. The results of the numerical analyses, expressed in terms of distribution of the amplification factor of peak acceleration and Housner intensity, proved that the topographic effects significantly influenced the ground motion at surface, whereas the role of cavities seemed to be negligible.