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Brittle Deformation

Brittle Deformation. Remember that q is the angle between s 3 and a plane. Definitions. Differential Stress: Difference between largest and smallest stresses Deviatoric Stress: Difference between total stress and mean stress. s 1. Magnitude of Normal and Shear Stresses. Normal.

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Brittle Deformation

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  1. Brittle Deformation Remember that q is the angle between s 3 and a plane

  2. Definitions Differential Stress: Difference between largest and smallest stresses Deviatoric Stress: Difference between total stress and mean stress.

  3. s1 Magnitude of Normal and Shear Stresses Normal s3 Shear

  4. What does this mean for fractures? Fractures will form when sn is low but ss is high. • is usually 60° when fractures form

  5. Coulomb Fracture Criterion predicts failure in rock: ss = sntanf fis the angle of internal friction tan fis the coefficient of internal friction Rocks: Avg. is 0.6 C is the point at which sn = 0 T is the point at which ss = 0 q= 90° -2f

  6. Shaded area is stable (No brittle failure) Failure No failure

  7. Sketch two cross sections: In one, 1 is horizontal, 3 vertical What is the dip of the fault predicted by this model? In the other 3 is horizontal, 1 vertical . What is the dip of the fault? Remember that q is the angle between s 3 and the plane. See also fig. 6.16. Exercise

  8. Once a fracture exists deformation continues by frictional sliding or cataclastic flow Frictional Sliding

  9. CCW Rotation

  10. Formation of Shear Fractures 2 faults form 1 fault stays active s3 s1

  11. These two are not faults. Crack is Parallel to 1

  12. Shallow crust Deep crust

  13. Non-frictional sliding on Fault surface: Calcite fibers from fluids in fault zone

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