We present an initiative aimed at fulfilling the requirement of the Ordnance 3274 (20 March 2003, Annex 1) of the Italian Prime Minister. This law established that a new seismic hazard map of the Italian territory be prepared within one year (April 2004) and stated the general compilation criteria. To comply with this request, INGV involved scientists and engineers from Italian scientific institutions along with its own researchers. Despite the tight schedule, the initiative utilised and further elaborated original information and knowledge acquired during the past few years. In particular, we compiled a new set of source zones (ZS9) - acknowledging new evidence of active faulting and recently acquired evaluations on seismogenic potential - and a new earthquake catalogue (CPTI04) extended to 2002. A limited-scale logical tree approach was adopted to explore epistemic uncertainties related to: i) the assessment of catalogue completeness based on historical and statistical methods; ii) the evaluation of seismicity rates, based on activity rates and G-R rates; iii) the assessment of Mmax, partly constrained by geological evidence; iv) the ground-motion attenuation models, where regional relationships have been used to complement the classical European and Italian relationships. The results consists of a map displaying the median values of 16 weighted branches in terms of PGA with 10% exceedance probability in 50 years, related to very stiff soil conditions. Although in many steps we made conservative choices, the resulting PGA distribution exhibits lower maximum values with respect to previous country-scale hazard maps. This is mainly due to: a) magnitude re-assessment; b) larger size of the source zones; c) more realistic completeness time-intervals; d) use of different depth in the source zones. The map was compiled under the review of an international board and will serve as input
The 2004 probabilistic seismic hazard assessment for the Italian area
GASPERINI, PAOLO;
2004
Abstract
We present an initiative aimed at fulfilling the requirement of the Ordnance 3274 (20 March 2003, Annex 1) of the Italian Prime Minister. This law established that a new seismic hazard map of the Italian territory be prepared within one year (April 2004) and stated the general compilation criteria. To comply with this request, INGV involved scientists and engineers from Italian scientific institutions along with its own researchers. Despite the tight schedule, the initiative utilised and further elaborated original information and knowledge acquired during the past few years. In particular, we compiled a new set of source zones (ZS9) - acknowledging new evidence of active faulting and recently acquired evaluations on seismogenic potential - and a new earthquake catalogue (CPTI04) extended to 2002. A limited-scale logical tree approach was adopted to explore epistemic uncertainties related to: i) the assessment of catalogue completeness based on historical and statistical methods; ii) the evaluation of seismicity rates, based on activity rates and G-R rates; iii) the assessment of Mmax, partly constrained by geological evidence; iv) the ground-motion attenuation models, where regional relationships have been used to complement the classical European and Italian relationships. The results consists of a map displaying the median values of 16 weighted branches in terms of PGA with 10% exceedance probability in 50 years, related to very stiff soil conditions. Although in many steps we made conservative choices, the resulting PGA distribution exhibits lower maximum values with respect to previous country-scale hazard maps. This is mainly due to: a) magnitude re-assessment; b) larger size of the source zones; c) more realistic completeness time-intervals; d) use of different depth in the source zones. The map was compiled under the review of an international board and will serve as inputI documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
