The collective displacements of points in a body is called deformation. The complete transformation from the initial to the final geometry of a body Involves:1.
Translation, 2. rotation, 3. dilation or volume change and 4. distortion or shape change. All four may vary in proportion. e.g. in case of folding by flexural slip, translation accounts for much more than distortion or or volume change with only a small component of rotation. Various mechanisms lead to the deformation of the rock. The processes that do not lead to shape change on small scales are grain boundary migration, rotation recrystallisation and metamorphic reaction
elongation, stretch and quadratic elongation; shear strain; dilation; finite vs. infinitesimal; strain; strain ellipsoids; strain tensors; Mohr diagrams for strain; natural strain markers; pure shear vs. simple shear strain paths; elasticity, Young's modulus and Poisson's ratio; plastic behavior; viscous behavior; constant load creep test; compound viscous-elastic behavior - Maxwell body and firmoviscous; Kelvin body; definition of rheidity; effect of strain rate on deformational behavior; effect of confining pressure on deformational behavior; effect of temperature on deformational behavior; effect of fluids on; deformational behavior; composite strength profiles of crust; Kink bands and extended Mohr envelopes.
Deformation = change in material system configuration.
Components of deformation:
rigid body translation.;rigid body rotation.; internal distortion.; all three very common. Consider a listric normal fault.
Homogeneous vs. inhomogenous strain:
function of choice of scale.;during homogeneous strain a straight line stays straight.;
e.g. consider a fold;
inhomogenous on the whole.;may be approximately homogeneous within a limb or at the hinge.;
ductile shear zone:
typically inhomogenous as traverse entire zone.;homogeneous in interior, break down into smaller semi-homogeneous pieces and integrate.