Proceedings of the 12th International INQUA meeting on paleoseismology, active tectonic and archaeoseismology

secondary (or Distributed, DF) normal faults/fractures in response to slip on a Principal fault. The predictive equations were strictly empirical; they had physical basis via static or dynamic analysis. The most obvious trend for DFs in historic ruptures was that they are more frequent (Youngs et al, 2003, Fig. 9), and have larger displacements (Youngs et al, 2003, Fig. 11), the larger the earthquake is, and the closer the DF is to the PF. Equations regressed probability (or displacement) on the DF (dependent variable), against earthquake magnitude and distance between the PF and DF (two independent variables). Later, Petersen et al. (2011, Eq. 18) created a similar regression for strike-slip faults, but admitted that there was “a weak correlation with magnitude (m) and distance (r, in meters) from the rupture.” This was probably due to the small number of ruptures they analyzed (8) and the small number of displacement measurements on DFs. The IAEA (2021) monograph on PFDHA was based on these two early studies. Recognizing the limited data sets and high uncertainty in the early empirical studies, IAEA stated: “Therefore, in the context of site-specific PFDHA, the physics-based numerical simulations, capturing details of the site of interest for fault displacement prediction, can complement the empirical models and available data to improve the representation of the site of study and to be consistent with the non-ergodic process of natural earthquakes.” (underlining added). In the early 2020s several updated analyses were published on PF and DF surface rupture statistics (Sarmiento et al., 2021; Moss et al., 2022; Nurminen et al., 2022). In particular, the number of DFs and their displacements increased by orders of magnitude, based on post-earthquake surveys such as Villani et al. (2018), which measured 5,200 surface offsets after the 2016 Norcia rupture. That single investigation contained 10 times more slip measurements on DFs than all previous studies combined. Starting in the mid-2010s in Fennoscandia, and later in Canada (Blanksma et al., 2022), high-level nuclear waste repositories were being designed to identify and accommodate possible earthquake- induced slip on fractures and faults within the repository volume. This task was handed to rock mechanics experts rather than to geologists and seismic hazard analysts. In the case of the proposed Forsmark repository in Sweden (Fig. 1), Fälth et al. (2015) stated “However, to our knowledge no attempts have been made to quantify the amount of slip that could potentially be induced on fractures in the near field of an earthquake.” Four years later, Hökmark et al. (2019, p. 8) concluded: “In the terminology