Vocabulary Terms
You should be able to define the following terms.
| Joints | veins | joint set | joint system |
| shear fractures | slickenlines | crystal fibers | structural domain |
| en echelon | fringe | hackles | ribs |
| plumose structure | origin | Mode I, II, and III | Y-, X-, T-intersections |
| Tensile Strength (T0) | Cohesive Strength (s0) | Angle of internal friction (f) | Critical Shear Stress (sc) |
| Coefficient of internal friction | asperities | angle of sliding friction (ff) | Coefficient of sliding friction (mf ) |
| gouge | pore fluid (Pf) | effective stress (s*) | fluid pressure ratio (l) |
| hydrofrac | rift | grain | Tectonic joints |
| release joints | unloading joints | cross joints | longitudinal joints |
| Stretching surfaces | shatter cones | Griffith Cracks |
Concepts
You should be able to give short answers to the following questions:
1.) How are structural domains defined?
2.) Identify the ornamentation on a joint plane and discuss its significance to joint formation and propagation.
3.) Distinguish between Mode I, Mode II, and Mode III fractures.
4.) How can joint intersections be used to determine the relative ages of joints?
5.) How do the failure envelopes and the type of fractures that can develop change as a function of the confining pressure? (confining pressure relative to T0)You should answer this by drawing a Mohr Circle for Stress diagram which includes the complete failure envelope (e.g., tensile, transtensional or parabolic, Coulomb, and Von Mises). Review Griffiths Law as well.
6.) What is the approximate ratio of critical stress to normal stress needed to cause brittle failure of most rocks? How do you derive at this value?
7.) What is Byerlee's Law?
8.) Given the stress conditions and the Failure envelopes for intact and fractured rock be able to determine the conditions under which old fractures of a given orientation will reactivate or whether new fractures will form instead.
9.) Using a Mohr Circle for Stress Diagram, discuss the influence of Pore Fluid Pressure on fracture formation.
10.) Interpret paleostress directions for s1 and s3 from joint orientations (pp. 261-265).