Earlier studies focusing on single shear bands reported a narrow range of thicknesses; 0.15 to 1.5 mm (Engelder 1974) and 0.7 to 1.2 mm (Aydin, 1978). More recent surveys revealed single shear bands as thick as 5 mm (Figures 1(a) and (b); from Fossen et al., 2007) and suggested variable shear band thickness with grain size; generally, thicker bands occurring in medium- to coarse-grained sandstones. Apparently, shear band thicknesses cannot be correlated with the shear displacements (Figure 1(a)), which will be revisited in the scaling section.

Figure 1. (a) and (b) showing thicknesses of shear bands with two distinct mechanisms; cataclastic and what the original authors referred to as disaggregation bands. Thicknesses up to 5 mm have been measured. Generally, shear bands are thicker in medium- to coarse-grained sandstones deformed without grain fracturing, and according to the original authors, band thicknesses show no correlation to the maximum shear displacements ((a) from Fossen et al. (2007), (b) constructed by the present authors using the thickness data in (a)).

Figure 2 shows frequency-thickness data collected from shear bands in the carbonate grainstone cropping out in the island of Favignana, west of Sicily (Tondi et al., 2012). The data shows that the thickness distribution for shear bands (both single and zone, blue and red, respectively) in the carbonate grainstone is limited in magnitude and is linear and flat in form but the well-developed shear bands with slip surfaces (green in the figure) have a strikingly different trend with a high inclination.

Figure 2. Cumulative frequency distributions of thicknesses for single shear bands (in blue), zones of shear bands (in red), and shear band zones with slip surfaces (in green) in carbonate grainstone, the island of Favignana, west of Sicily. The line fits for the single bands and zones have very small slope; on the other hand, the line fit for band zones with slip surfaces are highly inclined. From Tondi et al. (2012).