GNGTS 2023 - Atti del 41° Convegno Nazionale

Session 2.1 GNGTS 2023 limit of the Nurminen et al.’s model is that this is not a complete model for DRs, as it does not account for DRs deriving from reactivation of pre-existing structures of from structurally complex settings. In this work we explore the characteristics of DRs from the analysis of numerous historical reverse and normal surface ruptures contained in a new release of the ‘SUrface Ruptures due to Earthquake (SURE)’ database (SURE 2.0, Nurminen et al., 2022), within which the ruptures are categorized based on geological information (ranking of ruptures). The aim is to obtain predictive regressions for the probability of occurrence and expected displacement for distributed rupturing during dip-slip earthquakes that account for the different expected typologies of DRs. DATA We used empirical data compiled in a new release of the SURE database (Baize et al., 2019), named SURE 2.0 (Nurminen et al., 2022). The SURE 2.0 database contains surface rupture data (rupture traces and slip observations) from 50 crustal earthquakes (depth ≤ 25 km) occurred worldwide, 16 of which with strike-slip, 18 normal, and 16 reverse kinematics, with Mw ranging from 4.9 to 7.9. In particular, we analysed surface ruptures from normal (Mw 5.6 – 7.5) and reverse (Mw 4.9 – 7.9) earthquakes. A significant novelty of the SURE 2.0 database is the surface rupture categorization (ranking) based on geological and structural information. SURE 2.0 distinguishes 6 different rupture types, (Fig. 1): Rank 1 is the principal fault rupture (PF), corresponding to the surface expression of the movement along the fault plane responsible for the release of the seismic energy during an earthquake, as previously defined by Youngs et al. (2003). PF has the most continuous surface expression, and generally the highest displacement. PF often occurs on fault traces that have the potential to be known and mapped prior to the earthquake, i.e., faults with long-term geologic and geomorphic evidence of activity. All the surface rupturing off the PF is considered distributed rupturing and has ranking > 1. Rank 2 is for simple distributed ruptures, which include discontinuous surface breaks around the PF that occurred as a direct response to the movement along the earthquake fault. Rank 2 DRs occur rather randomly around the PF trace, and the measured displacements are remarkably lower than the PF nearby. The occurrence of rank 2 DRs is largely guided by subsurface material and complexities of the PF. Rank 2 DRs are frequent around PF complexities, such as bends or stepovers. This is the most common DR type in earthquakes of all kinematics. Rank 1.5 is for ‘primary’ DRs, indicating movement along pre-existing faults that have the potential to be recognized and mapped before an earthquake, as there can be geologic and geomorphic evidence of long-term activity on them. Rank 1.5 is applied only to cases when geological data (e.g., geologic maps and cross-sections) suggest these structures are pre-existing and directly