This lecture
• Last lectures Methods of • Mohr circle for strain Structural Geology • This lecture • Look at deformation history of individual lecture 6 lines/planes • Different deformation histories: same result? • The difference between pure and simple shear • Stretching & shortening
The Mohr circle for strain Vorticity
• A line that makes an angle with the X-axis " • Vorticity is the average rotation of lines • Stretches by a factor L • Vorticity is strain dependent • And rotates by an angle ! • Here: 7.5° " a b% Fij = $ ' # c d & L ! 2" The X-axis plots on {a,-c} 7.5° The Y-axis plots on {d,b}
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Kinematic vorticity number: Wk Wk and type of strain
• We need a "number" which tells us what the • Wk = 0 • 0 < Wk < 1 • Wk = 1 type of deformation is • Pure shear • General • Simple
• And that is independent of strain: Wk shear shear
W W = k R