Macroseismic attenuation relationships of Italian earthquakes for seismic hazard assessment purposes

In the frame of activities carried out in Italy for the seismic hazard assessment of the whole country, attenuation relationships were calibrated for macroseismic intensity. The attenuation curves follow the Grandori formulation, and were derived from the data sets of significant earthquakes; the results are presented and commented. Fifty-nine relationships, calibrated on more than 12 000 intensity observations, have been chosen to represent the regional patterns of intensity expected from some design earthquakes: this regionalization has seismic hazard purposes and has already been introduced into the national seismic hazard assessment. All the attenuation coefficients have to be used jointly with the earthquake catalogue, or linked to the present seismogenic zonation; both are prepared with the same hazard intent by the National Group for the Defence against Earthquakes. The reliability of these relationships is commented in relation to one mean curve derived from the same subset of macroseismic observations; even if the global residuals distribution does not favour the use of a multiple-law approach, a deeper analysis shows that the proposed regionalization gives a significantly better image of near- field damage, representing a first step towards a deterministic treatment of attenuation in probabilistic seismic hazard analyses.