GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 The macroseismic approach to Probabilistic Seismic Hazard Assessment: the SASHA 2.0 code V. D’Amico 1 , D. Albarello 2,3 1 Istituto Nazionale di Geofisica e Vulcanologia, Pisa, Italy 2 Dept.of Physics, Earth and Environmental Sciences, University of Siena, Italy 3 Consiglio Nazionale delle Ricerche, Istituto di Geologia Ambientale e Geoingegneria, Rome, Italy Documentary data relative to local effects of historical earthquakes play a major role in extending time coverage of parametric seismic catalogues. Thus, in the last tens of years, many efforts have been devoted to retrieve new reliable information about pre-instrumental earthquakes aiming at characterizing the seismogenic processes to feed PSHA computation based on the standard Cornell-McGuire approach. Actually, a large part of the Italian catalogue of main earthquakes relies on Intensity data to infer macroseismic magnitudes and macroseismic epicentres of historical events. However, this use of intensity data does not exploit the whole potential of this piece of information which inherently concerns site specific data. To take advantage of this last feature, a different use of macroseismic information has been proposed in the frame of a coherent PSHA approach which accounts for the specific characteristics of Intensity data (ordinal and discrete over a finite range) without any forcing of the relevant information into a para-instrumental frame. This approach (implemented in the code SASHA) provides hazard estimates at each site by considering the macroseismic history of each Municipality or site eventually integrated by data relative to neighbouring localities. In SASHA, the whole macroseismic data set is considered by also accounting for uncertainty affecting original data, the completeness of local information (no time truncation is considered) in the frame of a distribution free approach to estimate recurrence probabilities. Outcomes of this computational tool also accounts for the eventual presence of site effects (stratigraphical and morphological). Moreover, since intensity data are representative of the seismic effects on a settlement, outcomes of SASHA may be considered for preliminary (and rough) risk estimates. In the last years, the SASHA approach has been upgraded to allow deaggregation analyses, to provide outcomes supporting liquefaction studies, to identify situations where site effects may play a major role in the local seismic hazard. Moreover, specific outcomes have been provided in terms of a response uniform hazard spectrum which can be considered as a useful benchmark for studies based on the standard Cornell-McGuire approach at sites where a rich seismic history is documented. Some of these new applications will be presented to illustrate performances of this new version of the SASHA code.