Earthquake-induced crustal deformation and consequences for fault displacement hazard analysis of nuclear power plants

Abstract

Readily available interferometric data (InSAR) of the coseismic deformation field caused by recent seismic\ud events clearly show that major earthquakes produce crustal deformation over wide areas, possibly resulting\ud in significant stress loading/unloading of the crust. Such stress must be considered in the evaluation\ud of seismic hazards of nuclear power plants (NPP) and, in particular, for the potential of surface slip (i.e.,\ud probabilistic fault displacement hazard analysis - PFDHA) on both primary and distributed faults.\ud In this study, based on the assumption that slip on pre-existing structures can represent the elastic\ud response of compliant fault zones to the permanent co-seismic stress changes induced by other major\ud seismogenic structures, we propose a three-step procedure to address fault displacement issues and consider\ud possible influence of surface faulting/deformation on vibratory ground motion (VGM). This\ud approach includes: (a) data on the presence and characteristics of capable faults, (b) data on recognized\ud and/or modeled co-seismic deformation fields and, where possible, (c) static stress transfer between\ud source and receiving faults of unknown capability.\ud The initial step involves the recognition of the major seismogenic structures nearest to the site and\ud their characterization in terms of maximum expected earthquake and the time frame to be considered\ud for determining their ‘‘capability” (as defined in the International Atomic Energy Agency - IAEA\ud Specific Safety Guide SSG-9). Then a GIS-based buffer approach is applied to identify all the faults near\ud the NPP, possibly influenced by the crustal deformation induced by the major seismogenic structures.\ud Faults inside these areas have to be tested for ‘‘capability” according to the same time window defined\ud for the primary seismogenic structures.\ud If fault capability is confirmed or, eventually, cannot be assessed, the next step is to implement an\ud approach based on the potential to affect the safety of the NPP site in terms of fault geometry, and potential\ud displacement.\ud Finally, in the case where the fault can affect the safety of the site, the third step is the PFDHA or, in\ud other words, the calculation of the annual probability of exceedance of the potential co-seismic fault displacement;\ud this displacement is to be compared with the fault displacement threshold that will impact\ud the safety of the NPP site.\ud We also consider the effect of site vicinity tectonism on site vibratory ground motion and discuss an\ud example in the light of the use of the GMPE

Surface Faulting and Ground Deformation: Considerations on Their Lower Detectable Limit and on FDHA for Nuclear Installations

“…So far, systematic databases of earthquake-induced ground ruptures result in well-accepted scaling relations between earthquake size (i.e., usually expressed as moment magnitude M w ) and dimensions of the seismogenic structure (i.e., area, length, maximum displacement). Accordingly, recent works (e.g., Livio et al 2017, Gürpinar et al 2017) pointed out a similar close relationship between the areal extent and amount of surface deformation, as measured through InSAR imaging, and earthquake size.…”

“…Although the IAEA Safety Guide SSG-9 provides recommendations related to fault displacement hazards for nuclear installations, the actual application of these recommendations to concrete cases (particularly (2) and (3) conditions) needs a more quantitative framework. The previous papers by the authors (Livio et al 2017, Gürpinar et al 2017) and the present work constitute an attempt in this direction.…”

“…The previous discussion indicates an apparent lower limit of M w for earthquake-induced ground deformation, based on the analysis of empirical data sets of surface faulting. A similar approach has been recently used for the regression of the areal extent of earthquake-induced ground deformation against M w (e.g., Livio et al 2017, Gürpinar et al 2017). We here update that regression, including some recent earthquakes and adopting the same methods, as summarized in the following.…”

Conditional probability of distributed surface rupturing during normal-faulting earthquakes

“…The position at the surface of the antithetic structure is driven by factors such as the change in dip of the principal fault at depth (e.g., Caskey et al, 1996); this points to the possibility of introducing deterministic constraints in the estimation of the expected distributed faulting. Thus, we point out that the use of elastic dislocation models of deformation (e.g., Okada, 1985) and, in turn, of induced Coulomb stress transfer on receiving preexisting faults (e.g., Toda et al, 2011) may be useful for more accurately predicting the probability of DF (e.g., Gürpinar et al, 2017;Livio et al, 2017), especially where the current models show higher residuals (e.g., at ca. 7-12 km in the hanging wall).…”

Characterizing the Distributed Faulting During the 30 October 2016, Central Italy Earthquake: A Reference for Fault Displacement Hazard Assessment

“…A quantitative correlation between observed DF, elastic dislocation models, and observed deformation fields, as captured by geodetic methods, can contribute to understanding how strain partitions. This, in turn, will lead to the definition of weighted factors to be implemented in PFDHA procedures, as recently suggested by Gürpinar et al ().…”