GNGTS 2019 - Atti del 38° Convegno Nazionale

322 GNGTS 2019 S essione 2.1 of multi-fault earthquakes not well constrained and considered. However, the 2016 central Italy seismic sequence showed the two distinguished active normal faults can rupture at the same time during one seismic event (Pucci et al. , 2017). In addition, palaeoseismology (Galli et al. , 2010) and structural geology (Iezzi et al. , 2019) suggest that multi-fault earthquakes can occur within the Apennines. Therefore, I believe that is necessary to apply a modern fault-based seismic hazard approach that includes the occurrence of multi-fault earthquakes, where seismic ruptures can rupture multiple faults during the same event, and that relaxes fault segmentation (Field et al. , 2014, Visini et al. , 2019). In this sense, the latest Uniform Californian Earthquake Rupture Forecast version 3 (UCERF3) yields estimates of the magnitude, locations, and frequency of earthquakes using a fault source model that includes about 270 faults, throughout the California region, relaxing fault segmentation and allowing multi-fault rupture. UCERF3 model framework is composed by four main components: the fault model, the deformation model, and the earthquake rate and probability models. The former gives the geometry and kinematic information of the active faults located in the region and it is necessary to define all possible ruptures combination, the deformation model gives slip-rate for each fault section, the earthquake rate model provides the long-term rate of all possible earthquakes, and the latter gives the likelihood that each event will occur during a specified time span. In this work, I adapted the time-independent UCERF3 framework in central Italy defining a fault model, composed by 25 fault sections that yield 95 subsections, and assigning at each subsection a slip rate value through a deformation model. Then, I computed the long-term earthquake rates of all possible ruptures via a standard inverse approach. The comparison of the MFDs computed among this approach, the common used approach in Europe and central Italy (i.e. using individual seismogenic sources), and the observed historical rates highlights the necessity to consider a model that relaxes segmentation and consider the multi-faults events in order to better reproduce the observed data and avoid an under/over prediction of the expected activity rates that could lead to a wrong estimate of the hazard. I tested only the time-independent UCERF3 model in central Italy, but due to its hierarchy, with the time-dependent probabilities conditioned on the time-independent model, and the short term clustering model conditioned on the time-dependent model, I can claim that the UCERF3 model framework is suitable for Italy, with a list of mandatory things to do before: (1) mapping all the active faults throughout the country, realizing a quaternary active faults database, (2) compilation of a database with measured and dated geological offsets in order to assign slip rate values at subsection levels, and (3) compilation of a uniform paleoseismological database that contains information about the mean recurrence times of events and slip-per-event information. References Field, E. H., Arrowsmith R. J., Biasi G. P., Bird P., Dawson T. E., Felzer K. R., Jackson D. D., Johnson K. M., Jordan T. H., Madden C., et al. (2014). Uniform California Earthquake Rupture Forecast, version 3 (UCERF3) -The time-independent model, Bull. Seismol. Soc. Am. 104 , no. 3, 1122–1180, doi: 10.1785/0120130164. Field, E. H., & Jordan, T. H. (2015). Time-dependent renewal-model probabilities when date of last earthquake is unknown. Bulletin of Seismological Society of America , 105 (1), 459–463. https://doi.org/10.1785/0120140096 Galli, P., Galadini, F., & Pantosti, D. (2008). Twenty years of paleoseismology in Italy. Earth - Science Reviews , 88 (1– 2), 89–117. https://doi. org/10.1016/j.earscirev.2008.01.001 Galli, P., Giaccio, B., & Messina, P. (2010). The 2009 central Italy earthquake seen through 0.5 Myr-long tectonic history of the L’Aquila faults system. Quaternary Science Reviews , 29 (27-28), 3768–3789. https://doi. org/10.1016/j.quascirev.2010.08.018 García-Mayordomo, J., Gaspar-Escribano J. M., & Benito B. (2007). Seismic hazard assessment of the Province of Murcia (SE Spain): Analysis of source contribution to hazard, J. Seismol. 11 , no. 4, 453–471, doi: 10.1007/ s10950-007-9064-0. Iezzi F., Roberts G., Faure Walker J., & Papanikolaou I.D. (2019). Occurence of partial and total coseismic ruptures of segmented normal fault systems: Insights from the Central Appennines, Italy. Journal of Structural Geology , 126, doi:10.1016/j.jsg.2019.05.003.