GNGTS 2022 - Atti del 40° Convegno Nazionale

GNGTS 2022 Sessione 2.2 355 FIRST SEISMIC IMPACT ANALYSIS FOR PRE-ERUPTIVE EVENTS IN ISCHIA G. Zuccaro 1,2 , D. De Gregorio 1 , F.L. Perelli 2 1 Department of Structures for Engineering and Architecture, University of Naples “Federico II” 2 LUPT-PLINIVS Study Centre, University of Naples Federico II, Napoli, Italy Introduction . Subject of this abstract is the development of first seismic impact analysis for pre-eruptive events in Ischia, based on exposure analysis conducted in the framework of agreements between the Department of Civil Protection and the PLINIVS Study Centre. The assessment of seismic impact in Ischia has been conducted through scenario analysis, estimating the probabilistic distribution of damage induced by a single seismic event (reference scenario), as a convolution of the three random variables: hazard, exposure and vulnerability [1]. Hazard is the probability of occurrence of a single event, of a given severity, in the specific area and in a specific period. Exposure is the geographical distribution in quantitative and qualitative terms of the different elements at risk that characterize the area under consideration (buildings and occupants), whose conditions and/or functioning may be damaged, altered or destroyed due to the occurrence of the seismic event. Vulnerability is the sensitivity of an exposed element to the natural event. It can be evaluated as the probability that the exposed element will suffer a certain level of damage or change of state, with reference to an appropriate scale, because of a natural event of assigned intensity. According to INGV-OV, as reference hazard has been chosen the last event that occurred having more energy, taken from the Parametric Catalogue of Italian Earthquakes CPTI15, version 2.0 [2]. The exposure assessments are conducted based on data collected, while the vulnerability curves adopted are those developed by the authors through empirical approach from the analysis of damage induced by earthquakes occurred on the Italian territory. The damage on people and buildings has been assessed by the E.A.S.E. model, a procedure developed by the PLINIVS Study Centre in which the investigated area is discretized in a grid with cells of 250 m x 250 m and defines, for each cell, a hazard value and an exposure. The outcomes of the model are the probable number of lost and unsafe buildings, and the probable number of deaths, injured and homeless. In this work only the estimation of lost and unsafe buildings is presented. The Hazard. The event of 21 August 2017 (Lat. 40.738; Long. 13.897) of magnitude 3.91 and depth 1.5 km, inferred from the Parametric Catalogue of Italian Earthquakes CPTI15, version 2.0, has been adopted as the reference hazard. Immediately after the event, INGV developed andmade available a shake-map that provides an immediate visualization of the shaking level of the affected area. The shake-map reports the peak values recorded by accelerometers and seismometers, mainly provided by the National Accelerometric Network (RAN) of the Civil Protection Department and by the National Seismic Network (RSN) of INGV, present in the area of the earthquake. Where no observed values are present, the software interpolates the data using ground motion attenuation laws, which are empirical laws for predicting shaking parameters as a function of distance, magnitude and ground conditions. The confidence of a shaking map is a function of the density of recording stations contributing to the calculation. The case of the Ischia earthquake is particularly complex and difficult to make an accurate reproduction of the real shaking observed using the ShakeMap procedure because: • there is only one usable datum on the Island of Ischia (IOCA seismic station, accelerometric sensor, located at the Casamicciola Observatory);