Anderson’s theory of faulting

1 / 25

# Anderson’s theory of faulting - PowerPoint PPT Presentation

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. Primary assumptions.

I am the owner, or an agent authorized to act on behalf of the owner, of the copyrighted work described.

## Anderson’s theory of faulting

Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author.While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server.

- - - - - - - - - - - - - - - - - - - - - - - - - - E N D - - - - - - - - - - - - - - - - - - - - - - - - - -
Presentation Transcript
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.

Primary assumptions
• Surface 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 rocks
• Coulomb behavior
Three possible stress combinations

Hypothetically requires 2 of the 3 principal stresses to be parallel with the surface of the earth

What are they?

What kind of faults would you expect at each?

σ1 horizontal, σ3 vertical — reverse faults
• σ1 vertical, σ3 horizontal — normal faults
• σ1 horizontal, σ3 horizontal — strike-slip faults
Most rocks have an angle of internal friction ≈ 30°

What dip angles does Anderson’s theory predict for

• σ1 horizontal, σ3 vertical — reverse faults?
• σ1 vertical, σ3 horizontal — normal faults?
• σ1 horizontal, σ3 horizontal — strike-slip faults?
Hypothetically

Reverse faults: should form at ~30° dip

Normal faults: should form at ~60° dip

Strike-slip faults: should form at ~90° dip

Can you think of any exceptions??

Common exceptions
• Thrust faults— mechanically unfavorable
• Low-angle normal faults— mechanically very unfavorable
Possible explanations
• Elevated pore fluid pressure
• Pre-existing weaknesses
• Rolling-hinge model for low-angle normal faults

σs

High Pf can lower effective stress

σ1eff

σ1

σn

σ3eff

σ3

σs

This can activate slip on a low-angle fault

σn

σ3eff

σ1eff

σs

However, if cohesive strength is sufficiently low...

σn

σ3eff

σ1eff

σs

It also doesn’t work well for low-angle normal faults

σn

σ3eff

σ1eff

2. Pre-existing anisotropy
• Bedding
• Weak layer (salt, shale)
• Foliation

East Humboldt

Range

Ruby

Mountains