GNGTS 2021 - Atti del 39° Convegno Nazionale

231 GNGTS 2021 S essione 2.1 PROBABILISTIC FAULT DISPLACEMENT HAZARD ANALYSIS, A CASE STUDY FROM THE UPPER TIBER VALLEY (ITALY): THE ANGHIARI FAULT. A. Testa 1 , A. Valentini 1 , P. Boncio 1 , B. Pace 1 , F. Visini 2 , F. Morelli 1 , F. Mirabella 3 , C. Pauselli 3 , M. Ercoli 3 1 Università “G. D’Annunzio” di Chieti 2 Istituto Nazionale di Geofisica e Vulcanologia 3 Università degli Studi di Perugia Ground surface faulting constitutes a localized source of hazard due to the occurrence of slip along an active and capable fault during a strong earthquake (i.e. primary faulting), and at certain distance from the fault (i.e. distributed faulting). Evaluating the fault displacement hazard, that is quantifying the probability of exceedance of surface slip in a given time frame from primary and distributed faulting, is crucial for infrastructure like lifelines or power plant, but also for dam, emergency facilities and pre- existing buildings. Several historical and recent earthquakes prove that fault displacement hazard represents a source of risk for urban environments in the Italian peninsula (Guerrieri et alii, 2009). At the moment, the seismic microzonation (Gruppo di lavoro ms, 2008) represents the only tool that considers the fault displacement hazard in Italy. One common approach to this kind of hazard is the zoning and the avoidance of the site characterized by the causative fault, but sometimes facilities may have not this option. For this reason and starting from the pioneering work of Youngs et alii (2003), several authors have developed a probabilistic approach to analyse this kind of hazard (Petersen et alii, 2011; Moss & Ross, 2011; Takao et alii, 2013; Nurminen et alii, 2020) for different style of faulting. This methodology is known as fault displacement hazard analysis (PFDHA). In this work, the earthquake approach proposed by Youngs et alii (2003) has been applied to the Anghiari fault, a NW-SE striking, NE dipping active and capable normal fault located in the northern Apennines (Italy). The probability of exceedance a displacement value, for both primary and distributed faulting has been evaluated for different locations along the strike of the fault and for different distances from it. Concerning primary faulting, the obtained value of displacement, for two different scenarios, lies between 55 and 130 cm for 2% of probability of exceedance and between 7 and 25 cm for 10% probability of exceedance in 200 years (1.900 and 10.000 years of return period, respectively). In terms of distributed ruptures, the resultant hazard is only a few percent of the primary faulting and decrease with increasing distance from the principal fault. References Gruppo di lavoro ms; 2008: Indirizzi e criteri per la microzonazione sismica. Conferenza delle Regioni e delle Province autonome - Dipartimento della protezione civile, Roma, 3 vol. e Dvd. Guerrieri L., Blumetti A.M., Di Manna P., Serva L. and Vittori E.; 2009: The exposure of urban areas to surface faulting hazard in Italy: a quantitative analysis. Ital.J.Geosci. (Boll.Soc.Geol.It.), Vol. 128, No. 1 (2009), pp. 179-189, 6 figs., 2 tabs. Moss R.E.S. and Ross Z.E.; 2011: Probabilistic fault displacement analysis for reverse faults. Bulletin of the Seismological Society of America, v. 101, no. 4, p. 1542-1553. Nurminen F., Boncio P., Visini F., Pace B., Valentini A., Baize S., Scotti O.; 2020: Probability of occurrence and displacement regression of distributed surface rupturing for reverse fault. Frontiers in Earth Science, doi: 10.3389/feart.2020.581605.