GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 Squaring the earthquake cycle: likelihood of surface faulting, repeated fault rupture and distributed faulting M. F. Ferrario 1 , M. Pizza 1 , F. Livio 1 , D. Schwartz 2 1 Università degli Studi dell’Insubria, Como, Italy 2 dFAULTconsult, Danville, CA USA The concept of the earthquake cycle has been proposed over 100 years ago and is at the core of seismic source characterization. Stress accumulates along fault planes and is released as slip during an earthquake; the dating of multiple earthquakes along a fault allows to calculate recurrence intervals. The hazard posed by fault displacement is critical for engineered structures, since mitigation measures are not available, or not viable on a large scale. In fact, when the avoidance criterion cannot be pursued, probabilistic approaches are adopted. The output of Probabilistic Faul Displacement Hazard Assessment (PFDHA) is a hazard curve that provides the probability of exceedance of a given displacement at a site. The PFDHA method has been introduced by Youngs et al. (2003) for normal faults and later applied to strike-slip and reverse faults (e.g., Petersen et al., 2011; Moss & Ross, 2011; Takao et al., 2013). PDFHA requires to compute three probabilities: i) the probability that surface rupture actually occurs for a given magnitude; ii) the probability that the rupture will reach the site of interest and iii) the probability that displacement exceeds a defined value. Existing PFDHA models are largely based on empirical datasets, which were developed several years ago; fault displacement hazard has attracted increased attention due to the tremendous consequences it may have on engineered structures and infrastructures. Additionally, the documentation of surface faulting has benefited from technological improvements (e.g., InSAR, Lidar): it is thus timely to update existing datasets, to derive new scaling laws and to introduce some factors that were not previously addressed in the realm of hazard assessment. Here we focus on the likelihood of primary faulting and on the repeated rupture of a single fault strand in a short time period; the two issues are described in the following. Likelihood of surface rupture It is well known that earthquakes with increasing magnitude have a higher chance to rupture the surface. Scaling laws that define the likelihood of surface faulting have been proposed for different earthquake kinematics; the input data for this analysis is a list of earthquakes that did / did not