This is one of the most common assemblages in nature and was dealt with in great detail somewhere else in this Knowledgebase. Please see the links entitled 'Splay Joints,' 'Faulting by Shearing of Single Set of Joints,' and 'Faulting by Shearing of Orthogonal Sets of Joints.' Here we review some results which have the same characteristics of fracture networks involving various types of faults and the related joints.

Figure 1 is a map showing a network of normal faults and joints in sandstone at Arches National Park, Utah. It shows many characteristics of faults and related joints, two end members of which are parallel and orthogonal trace geometries. Kattenhorn et al. (2000) interpreted these patterns in terms of perturbed stress fields due to the fault slip (Figure 2).

Figure 1. Joint patterns within the normal fault bounded blocks at Arches National Park, Utah. Areas (1) and (2) point out joints parallel and perpendicular, respectively, to the nearby fault traces. The joint-fault patterns other than the parallel and orthogonal ones also exist. From Kattenhorn et al. 2000.

Figure 2. Perturbed stress field associated with a slipping normal fault. From Kattenhorn et al. 2000. According to Kattenhorn et al., many of the common joint-normal fault relationships can be explained by the perturbed stress field around a fault.

One of the best studied fault-joint patterns is that of the Bristol Channel fracture network. Figure 3 shows a schematic diagram demonstrating strike-slip faults and the related joints. Rawnsley et al. (1992 and 1998), Petit et al. (2001), Bourne and Willemse (2001), and Maerten et al. (2006) studied the fault-joint patterns using a mechanical model based on elastic dislocations with extended sensitivity analyses. Again, it is straightforward to notice joints occurring sub-parallel to the faults in some areas, but in the central area of the diagram more complex intersection relationships including orthogonal and low-angle diagonal intersections are apparent.

Figure 3. One of the best examples of joint-strike-slip faults relationships was observed at Nash Point, Bristol Channel (UK) and was analyzed by several investigators including Rawnsley et al. (1998), Petit et al (2001), and Bourne and Willemse (2001). This idealized schematic diagram illustrates the faults and related joint patterns. From Bourne and Willemse (2001).

Ohlmacher and Aydin (1997) upon observing orthogonal and sub-parallel joints (and veins) and thrust faults, proposed that the frictional properties of the faults play an important role in the network patterns. Figures 4(a) and (b) provide a simplified version of their model for frictionless or very low friction coefficient along the faults to explain dual behavior of such a system as a function of the two most common angular relationships between the greatest compressive stress and the faults. For angles smaller than 45 degrees, the parallel fault-joint patterns are favored. For angles larger than 45 degrees, orthogonal fault-joint patterns are favored. Figure 4(c) is a plot showing the orientation of the local greatest compression as a function of the friction coefficient at mid points between two parallel faults.

Figure 4. Two end members of the joint-fault relationships are the parallel and orthogonal patterns which are dominant in both the Arches and the Bristol Channel examples. Here, the summary of two-dimensional analysis shows these end members (a and b) for frictionless faults subjected to far-field stresses at different orientations with respect to the faults. Faults with different friction coefficients would produce joints at different intersection angles as shown at the mid points of the fault-bounded blocks (c). From Ohlmacher and Aydin (1997). (a) and (b) redrawn from Fig. 17 of these authors.

The fact that faults are segmented in every scale suggests that fault tip lines play an important role in splay geometry and consequently in fault-joint relationships (Crider and Pollard, 1998). To this end, the readers are referred to the 'Splay Joints' and 'Fault Damage Zones' links given below.