Page 24 - Reservoir Geomechanics

9 The tectonic stress field

S v Normal B

S hmin T P
S Hmax

S v > S Hmax > S hmin

S v
Strike-slip

P B
S Hmax
S hmin

T
S Hmax > S v > S hmin

Reverse
S v
B

P T
S Hmax
S hmin

S Hmax > S hmin > S v

Figure 1.2. E. M. Anderson’s classification scheme for relative stress magnitudes in normal,
strike-slip and reverse faulting regions. Earthquake focal mechanisms, the beach balls on the right,
are explained in Chapter 5.

where ρ(z)is the density as a function of depth, g is gravitational acceleration and ρ is
the mean overburden density (Jaeger and Cook 1971). In offshore areas, we correct for
water depth
z

S v = ρ w gz + ρ(z)gdz ≈ ρ w gz + ρg(z − z w ) (1.6)
w
w
z w
3
where ρ w is the density of water and z w is the water depth. As ρ w ∼ 1 g/cm (1.0 SG),
waterpressure(hydrostaticpressure)increasesatarateof10MPa/km(0.44psi/ft).Most