Seismic hazard assessment from intensity data

Abstract

A new approach has been developed aiming at the probabilistic estimate of seismic hazard from the local seismic history. This is expressed in terms of seismic effects documented at the site during past earthquakes (macroseismic intensity) and thus a specific statistical treatment is required to take into account the peculiar character of macroseismic data that are discrete, ordinal and range-limited. The proposed procedure also allows the correct treatment of relevant uncertainty (ill-defined intensity values, local catalogue completeness, etc.) in the frame of a coherent distribution-free statistical approach. This methodology has been implemented in a free computer program (SASHA: Site Approach to Seismic Hazard Assessment) and applied to the seismic hazard estimation at the 8100 municipalities in Italy. The program also implements a probabilistic procedure to “translate” hazard estimates provided in terms of Intensity to other ground-shaking parameters (e.g. PGA): this “rescaling” procedure allows to com-pare the results coming from this approach with those provided by standard PSHA procedures. This comparison results of great importance at the sites where a relatively rich seismic history is available and it could provide a benchmark for different approaches to PSHA.