Presentation on theme: "Anderson’s theory of faulting"— Presentation transcript:
1 Anderson’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.
2 Primary 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
3 Three 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?
5 Most 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?
6 Hypothetically 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??
7 Common exceptions Thrust faults — mechanically unfavorable Low-angle normal faults — mechanically very unfavorable