Sensitivity analysis of parameters for probabilistic seismic hazard assessment of western Liguria (north-western Italy)

In this paper the sensitivity analysis is performed as the preliminary step towards the construction a logic tree useful for probabilistic seismic hazard analyses of western Liguria (north-western Italy). The sensitivity analysis is conducted for six strategic sites within the Imperia district, following a multi-parameter approach, and accounts for both mean hazard values and hazard values corresponding to different percentiles (e.g. 16th and 84th percentile). In this way not only is the effect of a parameter on mean hazard values determined but also its sensitivity for two percentiles. In the analysis presented in this paper, the influence of different seismic catalogues (epicentral parameters), source zone models, frequency-magnitude parameters, maximum earthquake magnitude values and attenuation relationships is considered. As a result, the sensitivity analysis can be used as objective criterion for the construction of a logic tree focusing efforts on the parameters with a greater effect on the hazard. The results, valid just for a medium-low-seismicity and short historical information area such as western Liguria and for a similar set of assumptions in the logic tree, show that the seismic catalogues and the frequency-magnitude parameters have the highest influence on mean PGA values corresponding to a 475-year return period and the 16th percentile while the attenuation relationships have the highest effect on the 84th percentile. Furthermore, we found that the seismogenetic zonations characterized by smaller source zones contribute most to the uncertainty in the hazard.