GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 1.1 GNGTS 2023 rupture the surface. Extant scaling laws were developed several years ago; we updated them by investigating earthquakes occurred more recently. We exploit the ISC-GEM catalogue, selecting Mw > 5.5 earthquakes occurred onshore between 1992 and 2018 at depth lower than 20 km. We made a review of published literature and we found unequivocal information on 88 events that ruptured the surface and 276 events that did not rupture. We derive scaling laws on the entire dataset and for different earthquake kinematics (normal; reverse; strike-slip) and geodynamic settings (e.g., stable continental regions). For normal and strike-slip faults we found a general good agreement with previous equations, while reverse faulting in our dataset shows a lower tendency to rupture the surface. The new equations can replace older ones or be included in a different branch of a logic tree. Repeated rupture of the same fault strand Some recent seismic sequences were characterized by the repeated rupture of the same fault strand in a short time interval. For instance, Mt. Vettore fault ruptured on August 24 th , 2016 and again on October 30 th , 2016; the Kumamoto fault ruptured twice in two days in April 2016. Such a process has not been adequately investigated so far, and we aim at filling this knowledge gap by providing a list of case histories of documented re-rupture. Our dataset comprised 34 cases of historical re-rupture on 25 fault segments globally. We categorize them into 4 classes according to the spatial pattern of surface faulting and the degree of overlapping. Implications for paleoseismology and hazard assessment Field observations documented that earthquake behavior and ground deformation may occur under different forms: not all the earthquake of a given magnitude rupture all the way to the surface; ground deformation may occur as brittle failure or as broad deformation (warping, tilting); surface faulting occurs along principal and distributed faults; and a single fault strand may undergo repeated rupture. Processes such as distributed faulting and re-rupture may not be the rule but may be more common than previously thought. A better understanding of earthquake behavior and an eventual refinement of recurrence models provides the grounds for an improved hazard assessment. We speculate about the role played by the different processes considering the stories that paleoseismic trenches can tell from a region that experienced principal and distributed surface faulting, and re-rupture (Figure 1). Will trenches tell the truth (lawful characters)? Or are they neutral – “a neutral character does what seems to be a good idea”? Or do they follow their whims like chaotic characters?