GNGTS 2017 - 36° Convegno Nazionale

GNGTS 2017 S essione 2.1 251 considering available information, including the use of expert judgment. For each possible value of the MI, the Bayes rule updates its (posterior) probability as soon as new observations become available using a custom likelihood function, which is based on a probabilistic distribution of the vulnerability index ν ind corresponding to the different structural vulnerability, and the observed mean damage grade μ D , following the formulation proposed by Lagomarsino and Giovinazzi (2006). From the posterior distribution two different intensity assignments have been implemented: 1) argmax : selecting the intensity value with the highest probability, or 2) weighted : taking the weighted average of the intensities corresponding to the three highmost probabilities. In Fig. 3 the posterior distributions and the corresponding intensity assignments are shown for the localities where RRDA damage grading was available, and considering a prior distribution based on the expected average intensity estimated from the official shake map (Faenza et al. , 2016). The intensity values officially assigned by INGV to these settlements (black triangles) to these localities are also shown, along with the distribution of the residuals, defined as the difference between the value estimated with the weighted approach and the value officially assigned. The size of the points is proportional to the number of grading used for the estimation. This number is also indicated for each target location, along with the number of grading with non-zero damage). For both the assignment approaches (argmax and weighted) the average residual is also indicated. Conclusions. An innovative methodology is proposed to provide a rapid estimation of macroseismic intensity in terms of EMS-98 based on the observed damage on the built environment. The results, despite based on a small number of grading, show a good agreement of the estimated intensities with respect to the ones officially assigned by INGV through Fig. 3 - Left: Posterior distribution of MI for the considered localities. In parenthesis the number of gradings with damage > 0 and the total number). The reference (official INGV) assignment is indicated by a black triangle. Intensity estimated with the both argmax and weighted approaches are also shown. Right: Distribution of residuals, defined as difference between estimated (weighted) and assigned intensity. The size of the points is proportional to the number of available grading. Vertical lines represent the average residuals, including the zero residual as reference.