If the user requires an offline consulting service, negotiation will take place. All the available technical information provided by the potential client will be transmitted to the CDO (Central Design Office) where a pool of specialists will prepare a technical and economical proposal. At this stage the experts may recommend the user to collect additional information, for instance by carrying out a site investigation, if needed. The study will start upon acceptance of the technical and economical proposal by part of the client.

The methodologies adopted for the offline service reflect the international state of the art in the fields of probabilistic seismic risk and soil dynamics. In particular our procedures allow to take into account the uncertainty associated with the parameters controlling soil behaviour and site amplification. For this reason, our methodologies are suited not only for specific sites, but also for vast territorial areas where geological and geotechnical information may be limited.

The seismic hazard at a specific location is evaluated by a probabilistic approach, considering a very large number of possible future earthquakes. Magnitude, epicenter location (or rupture surface if the fault dimensions are known) and annual occurrence frequency (recurrence rate) are associated to each possible earthquake. The recurrence rate, the magnitude and the event location are estimated from historical catalogues and statistical considerations. The seismic hazard at the bedrock is evaluated adopting suitable attenuation laws for rock whereas, at the same time, the frequency-dependent amplification functions of the soil deposit are defined by running a series of truly non linear finite element analyses of the soil column. The finite element analyses are carried out applying to the soil column several acceleration time histories (typically not less than 20), also taking into account the uncertainty of each relevant soil parameter. The hazard at the ground surface is determined by probabilistically “combining” the seismic hazard at the bedrock and the amplification functions via convolution. The characteristic magnitude and epicentral distance for each oscillation frequency are also computed by a numerical de-aggregation process. The analysis may also consider the epistemic uncertainty of both seismic and geotechnical models by a logic three approach, providing the hazard for various levels of confidence.

If a territorial microzonation analysis is required, the seismic hazard is evaluated for a grid of sites throughout the area. The hazard is evaluated at each grid node by a probabilistic approach, similar to the one outlined above. By looping this procedure for all the grid nodes, the desired hazard maps can be produced. Such maps are obtained for the ground motion parameters most relevant for the estimation of structural damage (e.g., PGA and spectral accelerations at different oscillation frequencies).