Incorporating results from seismic microzonation into probabilistic seismic hazard analysis: An example in western Liguria (Italy): Fid-Bau Portal

Incorporating results from seismic microzonation into probabilistic seismic hazard analysis: An example in western Liguria (Italy)

Barani, S. / Ferretti, G. / De Ferrari, R.

Abstract

Abstract This study presents a first attempt to couple two of the most important components of seismic risk mitigation strategies: probabilistic seismic hazard analysis (PSHA) and seismic microzonation. We show an application in the westernmost sector of the Liguria region in northwestern Italy, an area where strong earthquakes (up to about magnitude 6.5) occurred in the past producing hundreds of casualties. The final goal is to produce probabilistic seismic hazard maps for peak ground acceleration and spectral acceleration that incorporate site amplification (by amending existing ground motion attenuation models for rock conditions with an additional amplification term provided by microzonation studies) on a municipal scale. To this end, a partially non-ergodic approach is applied according to modern practice. Compared to conventional, ergodic hazard assessments for rock conditions and flat topography, such maps provide at a glance a finer picture of the actual hazard of the area under study, highlighting those sites where the ground motion hazard is dominated by local amplification effects. At these sites, the expected ground motions are up to twice the values resulting from the traditional, ergodic PSHA on rock. Besides hazard maps, results are also presented in terms of uniform hazard spectra for a number of target sites. Comparison with the isoseismal maps of past earthquakes have revealed a good agreement between the spatial distribution of the assessed hazard and that of felt intensities, with greater damage observed in areas presenting significant amplification effects and, consequently, a higher seismic hazard.

Highlights • We analyze the role of local geology on seismic hazard. • Site effects from seismic microzonation maps are incorporated into PSHA in a robust, fully probabilistic way. • Partially non ergodic, site-specific probabilistic seismic hazard maps are defined. • Site-specific hazard is up to twice the traditional, ergodic hazard on rock. • The hazard distribution agrees well with the damage distribution associated with past earthquakes.