illustration For of stress concentrations at grain contacts in a simulated sedimentary rock using photoelasticiy, see Plate 1 in N.J. Price, 1966, Fault and Joint Development in Brittle and Semi-brittle Rock. For illustration of variation in trends of dikes at Spanish Peaks, Colorado, reflecting variations in stress trajectories due to superposition of point stress on a regional stress field, see Ramsay, 1967, Figs. 2114, 2-15.
Fracture cleavage in banded gabbros, showing refraction across bands, Bardon Peak, Duluth, MN
PJH photo
Fracture cleavage in banded gabbros, showing refraction across bands, Bardon Peak, Duluth, MN
3
Fracture cleavage in banded gabbros, in thin section, shown to be Mode I fractures
3
3
Conditions to allow for refraction of fracture cleavage in banded gabbros
1st
3 3
2nd
Orthogonal sets of joints in Ankara Sandstone, Park City, Utah
PJH photo
3
1
Microfractures used to map stress trajectories in experiments of drape folding, after Logan et al., 1978
Fault plane
Slickenlines
Unit vectors defining fault geometry Stress components across fault
n normal to fault plane s parallel to slickenline on fault plane o Perpendicular to n and s (i.e. o = n x s)
S
stress vector normal component shear component component on fault parallel to o ( = S.o)
System to describe fault planes and slip directions
For illustration of variation in patterns of slip direction on faluts of maultiple orientations, with variation in symmtery of the state of stress, given by , see Twiss and Moores, 1992, Fig. 10-17.
) = )2
1
) 3 )
3
For example of fault population analysis for interpretingg principal stress orientations and magnitudes, see Angelier, 1989, J. Geol., Struct. v. 11 (1/2), p. 37-50 and Bergerat et al., 2007, Tectonophysics, v. 444, p. 93-110.
3
2
1
Permissible stress states (shaded) for slip on pre-existing fractures (after Angelier, 1989)
new faults
) = )2
1
) 3 )
3
reactivated faults
Constraints on estimating stress magnitudes, based on knowledge of the failure criterion for new faults (a), friction law for reactivation of faults (b), and vertical stress ( gh) (after Angelier, 1989).
l= t ns co
3
m=
cons t
2
1
Locating position of stress state on 3D Mohr diagram, knowing the angles, cos-1l and cos-1n, defining the pole to the fault plane
Geometry of calcite twinning on {0112}
Dynamic analysis of calcite
2 90o
1
T axes C axes
3
3
1=
2
C axes x T axes
Example of using calcite twins to determine principal stress directions in experimentally deformed marble (after Fig. 11-3 in Turner & Weiss, 1963, Structural Analysis of Metamorphic Tectonites.
Coarse fibers of calcite in folded calcite vein
C
C
Twins in coarse ca...