Generating Shake Maps: Conditional GMPE-based Ground Shaking Fields with Site Effects

Shake maps are useful tools for spatial mapping of the ground shaking for a given earthquake event. They are often used for calculating the empirical fragilities by associating the ground shaking level at a given building’s location to the observed damage at that location. Alternatively, the ground shaking can be mapped for a given earthquake event by using the ground motion prediction equations (GMPE’s). However, the GMPE’s often have a considerable prediction error and they usually do not consider the non-linear stratigraphic effects and the effect of topography. Ground-shaking fields can be generated according to the joint probability distribution of groundshaking at the locations of interest considering the spatial correlation structure in the ground motion prediction residuals and updated based on the registered ground shaking data. As alternative to the embedded coefficients in the ground motion prediction equations accounting for subsoil categories, site-specific stratigraphic non-linear relationships based on microzonation studies can be applied directly to the ground motion fields at the engineering bed rock level. It is also possible to apply topographic amplification/deamplification factors considering the shape of site slopes. An application of the proposed procedure in generating stochastic ground motion fields for the 2016 Amatrice Earthquake both for a given areal extent and for a class of residential masonry buildings damaged in the central Italy sequence is presented. Regarding the derivation of empirical fragilities, it has been demonstrated that explicit consideration of the spatial correlation in the prediction of ground-shaking fields and the site effects significantly affects the results.