Stress and faulting regimes

The type of fault that occurs for each stress combination gives rise to the name of stress faulting regime (Table 5.2). Notice that stresses may change in magnitude and direction with time at a given location (see stress map in Fig. 5.16 - other maps available at http://www.world-stress-map.org/). Furthermore, the same location may evolve through different stress regimes over geological periods of time. The stress regime can also change with depth at the same location. Changes of stress regime with depth are critical for defining the geometry of fluid-driven fractures.

Table 5.2: The Andersonian faulting classification system.

Faulting regime	Maximum principal	Intermediate principal	Minimum principal
	stress $S_1$	stress $S_2$	stress $S_3$
Normal	$S_v$	$S_{Hmax}$	$S_{hmin}$
Strike-slip	$S_{Hmax}$	$S_v$	$S_{hmin}$
Reverse	$S_{Hmax}$	$S_{hmin}$	$S_{v}$

Figure 5.16: World stress map http://www.world-stress-map.org/. The figure above shows directions of maximum horizontal stresses based on various types of field measurements. The orientation of maximum horizontal stress varies with location and is strongly influenced by plate movement and imparted tectonic strains.