Flow, deformation, and transport - Physical Processes in Earth and Environmental Sciences - page 161

amounts according to orientation such as the larger
compressive stress

vertical load will be 2 , smaller in magnitude than one of

the horizontal stresses (

2 3
horizontal stresses; second, increasing the horizontal stress
levels but by different amounts so the vertical load will be
the smaller stress

1 will be the vertical load and

1 ) and larger than the other ( 3 ).

Fault angles with respect to the principal stress 1 can be

predicted from Coulomb's fracture criterion, c 0

n , with the coefficient of internal friction (

1 2 horizontal stresses; and
third, increasing the magnitude of the stress in one direc-
tion and decreasing the stress in the other direction, so the

3 and

) and the

cohesive strength ( 0 ) both depending on the nature of

the rock involved. This criterion has been validated in

(a) (b) (c)

N Undeformed state

s 1

s 2

s 3

z 0

F 1

F 2

F 2

F 1

x 0

(d 1 ) (d 2 )

z 2

z 1

x 1 x 2

(e)

Fig. 4.99 Normal faults form to accommodate an extension in some section of the crust. (a) Anderson's model for the relation between a pair
of normal conjugate faults ( F 1 and F 2) and the orientation of the principal stress axes are shown. According to this model, normal faults form
when 1 is vertical (this will be the orientation of the principal strain axis S 3 ). (b) The stereographic projection (Cookie 19) for the model in
(a) is shown. (c) Considering an initial segment of the crust, normal faulting is a response of brittle deformation caused by extension, and
produces a progressive horizontal lengthening and vertical shortening by the formation of new faults (d 1 ) and (d 2 ). (e) An example of normal
faults cutting recent deposits (Loutraki, Greece).