Abstract
Abstract Damage zones of different fault types are investigated in siliciclastics (Utah, USA), carbonates (Majella Mountain, Italy) and metamorphic rocks (western Norway). The study was conducted taking measurements of deformation features such as fractures and deformation bands on multiple 1D scanlines along fault walls. The resulting datasets are used to plot the frequency distribution of deformation features and to constrain the geometrical width of the damage zone for the studied faults. The damage-zone width of a single fault is constrained by identifying the changes in the slope of cumulative plots made on the frequency data. The cumulative plot further shows high deformation frequency by a steep slope (inner damage zone) and less deformation as a gentle slope (outer damage zone). Statistical distributions of displacement and damage-zone width and their relationship are improved, and show two-slope power-law distributions with a break point at c. 100 m displacement. Bleached sandstones in the studied siliciclastic rocks of Utah are associated with a higher frequency of deformation bands and a wider damage zone compared to the unbleached zone of similar lithology. Fault damage zones in the carbonate rocks of Majella are often host to open fractures (karst), demonstrating that they can also be conductive to fluid flow.
Highlights
Fault architecture, geometry and properties have formed key topics of interest across a range of disciplines through several decades (e.g. Caine et al 1996; Wibberley et al 2008; Bastesen & Rotevatn 2012; Torabi et al 2013; Gabrielsen et al 2016; Choi et al 2016)
Fault damage zones in the carbonate rocks of Majella are often host to open fractures, demonstrating that they can be conductive to fluid flow
Faulted siliciclastic rocks acquired from faults in Moab and the San Rafael Swell in Utah (USA), where Carboniferous–Cretaceous rocks were deformed in an extensional regime
Summary
Geometry and properties have formed key topics of interest across a range of disciplines through several decades (e.g. Caine et al 1996; Wibberley et al 2008; Bastesen & Rotevatn 2012; Torabi et al 2013; Gabrielsen et al 2016; Choi et al 2016). Cowie & Scholz 1992; Dawers et al 1993; Kim & Sanderson 2005; Kolyukhin & Torabi 2012), have been used to predict fault growth and evolution These statistical relationships are based on limited data that do not cover all ranges of fault sizes. Even though fault attributes and their scaling laws have been widely studied, there are still several issues that need to be addressed (e.g. Choi et al 2016) These include: (i) the inconsistent and nonuniqueness of definitions of fault geometrical attributes such as damage zone and fault core (Fig. 1); (ii) a lack of a proper constraint on fault dimensions (e.g. damage-zone width) that can be globally applied; (iii) inaccessibility of the fault structure including its damage zone in 3D; and (iv) gaps in the data and the scaling relationships between fault displacement and damage-zone width. Faulted siliciclastic rocks acquired from faults in Moab and the San Rafael Swell in Utah (USA), where Carboniferous–Cretaceous rocks were deformed in an extensional regime
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