Seismic hazard and strong ground motion: an operational neo-deterministic approach from national to local scale.

Recent advances in the physical knowledge of seismic waves generation and propagation processes, along with the improving computational tools, make it feasible the realistic modeling of the ground shaking caused by an earthquake, taking into due consideration the complexities of the source and of the propagation path. A neo- deterministic scenario based approach to seismic hazard assessment (NDSHA) has been developed that naturally supplies realistic time series of ground shaking, including reliable estimates of ground displacement readily applicable to seismic isolation techniques. The NDSHA procedure permits incorporating, as they become available, new geophysical and geological data, as well as the information from the different pattern recognition techniques developed for the space-time identification of strong earthquakes. All this leads to the natural definition of a set of scenarios of expected ground shaking at the bedrock. At the local scale, further investigations can be performed taking into account the local soil conditions, in order to compute the seismic input (realistic synthetic seismograms) for engineering analysis of relevant structures, such as historical and strategic buildings. The NDSHA approach has been already applied in several regions worldwide, including a number of local scale studies accounting for two-dimensional and three-dimensional lateral heterogeneities in inelastic media. A pilot application of the approach, including the detailed evaluation of the expected ground motion accounting for site effects and seismic engineering analysis, has been carried out at a site located in the Friuli Venezia Giulia Region (NE Italy). Further some applications worldwide of a new, highly efficient analytical methodology, developed for modeling the propagation of the seismic wavefield in three-dimensional inelastic media, are presented. This procedure, based on computer codes developed from a detailed knowledge of the seismic source process and the propagation of seismic waves in heterogeneous media, allows not only the detailed study of instrumental and macroseismic data but also the realistic estimate of the seismic hazard, in those areas for which scarce (or no) historical or instrumental information is available, and the relevant parametric analyses: different source and structural models can be taken into account to create a wide range of possible groundshaking scenarios from which to extract essential information, including uncertainty ranges, for decision making.