GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 RESULTS Overall, there are 13,078 slip data points for dip-slip earthquakes within the SURE 2.0 database. Over 1200 slip observations are from reverse events, 71% of which are for PF. The DRs of reverse events are nearly equally divided between simple (rank 2, 16%) and complex DRs (rank 1.5, 3, 21 and 22, 13%). For normal faults, there are ca. 11,800 data points, more than 80% of which is from the 2016 central Italy earthquake sequence, which dominates the database. The data points are nearly equally divided between PF (53%) and DRs (47%: 28% rank 1.5; 16% rank 2; 3% rank 3). By removing the 2016 central Italy data, the percentages of PF and DRs data points do not change drastically (66% and 34%, respectively). The cumulative length of all the surface rupture segments is ~1672 km, ~732 km for normal and ~940 km for reverse events. For normal events, 55% of the cumulative rupture length is for PF and 45% for DRs. The percentages do not change if the 2016 central Italy events are not considered. For reverse events, 72% of the cumulative rupture length is for PF and 28% for DRs. 3.1 Distance - frequency distribution of DRs by ranking Fig. 2 shows a histogram obtained by measuring the distances of DR rupture traces from the PF. We used a method that we call «slicing» (Nurminen et al., 2020), consisting of re-sampling the DR traces every 10 m, measuring the DR-PF distance (r), and counting the number of DRs within each 10 m-wide slice parallel to the PF. DRs can occur very far from the PF (up to ~20 km for normal events), but most of them concentrate near the PF (hundreds of meters from PF). Therefore, it seems possible to distinguish between near-fault and far-fault distributed faulting. Fig. 2. Frequency histograms of DR – PF distances for normal (a) and reverse (b) earthquake surface ruptures.