Localisation of deformation

The localization of deformation in geological materials is a widelystudied phenomenon at all scales, from the formation of deformation bandswithin single grains, up to crustal-scale shear zones (White et al., 1980;Poirier 1980; Hobbs et al., 1986). There is widespread evidence (in theform of faults, shear zones, fold hinges, etc.) that localization plays a ma-jor role in determining the mechanical response of rocks, and results intectonically and economically important structures. At each scale, andsometimes for each material, there is considerable speculation as to whichprocesses dominate the observed localization behaviour. In the mantle, lo-calization of deformation is necessarily much harder to document. It may,however, play a major role in controlling continental and mantle dynamicsand the observable seismic anisotropies (Ellis et al., 2001; McNamara etal., 2001). The purpose of this section is to demonstrate a simple simula-tion scheme capable of investigating spatial and temporal patterns of in-stantaneous and cumulative localization of deformation at the grain scale,using a two-dimensional numerical modelling scheme