GNGTS 2024 - Atti del 42° Convegno Nazionale

Session 2.1 GNGTS 2024 Causes and ways for modelling complexity in fault-based seismic hazard studies Bruno Pace Dipartimento di Ingegneria e Geologia, Università di Chieti-Pescara, Chieti, Italy Probabilistic fault-based and time-dependent seismic hazard studies are commonly used to forecast the time between consecutive earthquakes; however, the fault segmentation model and the slip rate variability over time are critical for obtaining accurate results. Complex coseismic ruptures observed in the last ~15 years (e.g., 2010 Mw 7.1 Canterbury NZ, 2012 Mw 8.6 Sumatra, 2016 Mw 7.8 Kaik ō ura NZ, 2016 Mw 6.5 central Italy, 2023 Mw 7.8 Turkey-Syria) have shown the need to consider different possible combinations of rupture scenarios. Moreover, geological and paleoseismological observations confirm the slip rate variability, but rarely seismic hazard models consider it. A possible explanation is the presence of networks of active faults, which interact in a complex manner. We present the results of some studies we have done on these topics. In terms of fault segmentation relaxation, we compare different methodologies to obtain fault-based seismic hazard estimates using several rupture scenarios combinations. In term of fault interaction, we show the importance considering the time-dependent viscoelastic relaxation of the lower crust and upper mantle as a possible additional source of stress changes at a regional scale to explain the concatenation of moderate-to-strong earthquakes. In addition to the development of realistic fault models (comprising detailed fault traces and geologic data to constrain surface and sub-surface fault geometry) and the collection of field observations (to constrain long-term slip rates), slip rate variability over time appears as another key parameter that needs to be considered in future fault-based seismic hazard models, given that both coseismic and postseismic processes are possible explanations of the observation. Finally, we suggest a way to better organize the fault data for a new generation of fault-based PSHA, with a transparent methodology to account for the best geological information available in a given region for seismic hazard and risk studies. The proposed approach empowers end-users and decision-makers to identify main fault and fault sections that participate the most to the seismic risk of a site.