Presentation on theme: "Anderson’s theory of faulting"— Presentation transcript:
1Anderson’s theory of faulting Goals: 1) To understand Anderson’s theory of faulting and its implications. 2) To outline some obvious exceptions to Anderson’s theory and some possible explanations for how these exceptions work.
2Primary assumptionsSurface of the earth is not confined, and not acted on by shear stresses.Also, tectonic plates move parallel with Earth’s surface (unknown in 1951)Homogenous rocksCoulomb behavior
3Three possible stress combinations Hypothetically requires 2 of the 3 principal stresses to be parallel with the surface of the earthWhat are they?What kind of faults would you expect at each?
5Most rocks have an angle of internal friction ≈ 30° What dip angles does Anderson’s theory predict forσ1 horizontal, σ3 vertical — reverse faults?σ1 vertical, σ3 horizontal — normal faults?σ1 horizontal, σ3 horizontal — strike-slip faults?
6Hypothetically Can you think of any exceptions?? Reverse faults: should form at ~30° dipNormal faults: should form at ~60° dipStrike-slip faults: should form at ~90° dipCan you think of any exceptions??
7Common exceptions Thrust faults — mechanically unfavorable Low-angle normal faults — mechanically very unfavorable