Eichhubl et al. (2004, 2005) measured and compared the capillary displacement pressures of fault rocks with smeared shale with respect to undeformed rock from the Hazel-Atlas Mine, Black Diamond Mine, California. The fault is a normal fault with 9 m of dip separation. The source shale layer is about 1.6 m and is attenuated to about 5 cm in the fault zone.

Samples are taken from the lowermost section of the hanging wall (Figure 1), where both deformed and undeformed shale are exposed. The capillary displacement pressures of deformed shale are reported to be 30% higher than the most clay-rich undeformed shale outside the fault (Figure 2). This increase in sealing capacity, in combination with a 50% anisotropy in capillary displacement pressure, is primarily attributed to the development of a planar fabric in deformed shale.

Figure 1. Schematic cross section across the Hazel-Atlas fault perpendicular to the fault surface. Samples are taken from the lowermost section of the shale layer in the hanging wall, indicated by circle. From Eichhubl et al. (2004).

Figure 2. Sample location zooming in the circular area in Figure 1 showing results of mercury displacement pressures Pd (Hg) and porosity of shale samples in situ and within the fault rock of the Hazel-Atlas fault, Black Diamond Mine, California. Filled circles indicate samples analyzed by mercury intrusion and empty circles for compositional and textural analyses. From Eichhubl et al. 2004.