Types and Causes of Induced Seismicity - Induced Seismicity Potential in Energy Technologies - page 21

ure 2a). The ratio of the mean horizontal stress to the vertical stress (Figure 2b) appears to vary over a narrower
range with increasing depth, the ratio being generally less than 1 at depths larger than 2 km (~1.2 miles).
The relative magnitude of the three principal stresses, σ h , σ H , and σ v , establishes the conditions for the
orientation of the faults. Three regimes of stress, each associated with different fault orientations, are commonly
defined (Figure 3): (a) thrust fault regime with σ v equal to the minimum principal stress, (b) normal fault regime

continued

(a) (b)

0 0

1

1

2

2

3

3

0 1 2 3 4

0 20 40 60 80 100

Vertical stress (MPa)

Figure 2 (a) Vertical stress variation with depth; the linear trend corresponds to a mean density of 2,700 kg/m 3 .
(b) Variation of the ratio of the mean horizontal stress ( σ H + σ h ) /2 over the vertical stress σ v with depth.
SOURCES: Figure modified from Jaeger et al. (2007), which was itself redrawn from the original figure of
Brown and Hoek (1978).

(a)

(b) (c)

Strike-slip fault

Thrust fault Normal fault

Figure 3 (a) Thrust fault, (b) normal fault, and (c) strike-slip fault. (Cross sections shown are in vertical plane
for (a) and (b) and horizontal plane for (c).)