New Developments in Seismic Risk Assessment in Italy

Abstract

The paper illustrates some improvements in the seismic risk assessments in Italy and describes the differences deriving from the use of different approaches to calculate the losses and the influence exerted by different hazard results. The first method of risk evaluation, here termed as 'direct', evaluates the losses by using only the mean values of the main variables involved (rate of events and frequency of the damage levels), thus providing an approximation of the expected losses. The second method, named 'probabilistic', takes into account the uncertainties related to the number of events (hazard) and the damage levels (vulnerability), thus determine the probability associated to each level of loss. Both methods express the risk as the economic losses to dwellings within a reference period of time. Two alternative hazard results are also used to show the influence on the calculated risk: the first one considering the seismicity uniformly distributed within seismic source zones; the second one clustering the strong seismicity in geographically narrowed source zones and scattering the low seismicity over large source zones.The results obtained show that the losses estimated by the 'direct' method are, at national level, a little bit lower than those obtained with the probabilistic method (about 6%). The differences are more pronounced at local level (regional or sub-regional), generally within ±20% with larger values in the zones of lower risk. Nevertheless, also the two hazard results show more pronounced differences at local rather than at national scale. The risk estimates in the high seismicity areas are greater if using the seismic hazard results based on the clustered seismicity, but the reverse is true, in the low seismicity areas, if using the hazard results based on the uniformly distributed seismicity.As a concluding remark, the direct method for calculating losses and the implementation of any seismic hazard result, may be acceptable for a general picture of the risk; whereas, when a detailed description of the territorial distribution of risk is needed, the probabilistic method for computing losses and a well-focused seismic hazard method should be used, as they are more pertinent to describe and highlight local differences.Abbreviations: GdL96 -hazard and risk results from the 'Working Group, 1996'; SCS -hazard and risk results from the 'Spatially Clustered Seismicity' model; SSN -seismic and risk results from the 'National Seismic Survey'.

Deriving vulnerability curves using Italian earthquake damage data

“…The use of DPMs is still popular in Italy and proposals have recently been made to update the original DPMs of Braga et al (1982). Di Pasquale et al (2005) have changed the DPMs from the MSK intensity scale to the MCS scale (Mercalli-Cancani-Sieberg) because the Italian seismic catalogue is mainly based on this intensity and the number of buildings has been replaced by the number of dwellings so that the matrices could be used in conjunction with the 1991 Census data, collected by ISTAT (Italian National Institute of Statistics). Dolce et al (2003) have also adapted the original matrices by adding a vulnerability class D, using the EMS98 scale (Grünthal 1998), to account for the buildings that have been constructed since 1980, which should have a lower vulnerability as they would either have been retrofitted or designed to recent seismic design codes.…”

A Mechanic Based Model for Definition of Seismic Risk and Real Time Damage Scenario of Buildings

“…Every 10 years a survey takes place and, among other information, data on material of construction, number of storeys and age of construction of buildings are collected and shared. Starting from these data, within each municipality, the building stock was classified in five category where the vulnerability class is connected with the age of construction according to [6] and the date of seismic classification of the municipality for masonry and reinforced concrete (RC) buildings. By comparing the seismic zone to which the municipality was assigned to the period of construction, it was possible to identify if residential buildings were designed or not according to the seismic design provisions.…”

Seismic Hazard of Urban Areas: A Case-Study

“…they have an unsatisfactory seismic capacity. In the last decades, many procedures have been developed to check the seismic vulnerability of urban areas [5,6,7,8,9], which can be divided into three main groups: the empiric, the analytical and the hybrid methods. The vulnerability analyses are focused on the reliability of the buildings with regard to the seismic actions expectable for the area.…”