We have studied the initiation of salt diapirs with frictional
overburdens under lateral compression and extension. The overburden is
assumed to be elasto-plastic with Mohr-Coulomb yield criterion and
non-associated flow rule. Plastic flow localizes into narrow shear bands
which may represent faults. The geometry and the evolution of these
shear zones are simulated for various theological parameters. The
dilational and frictional properties of frictional overburdens are found
to be important controls on the types of shear zones formed in lateral
compression and extension. The friction and dilation angles influence
the angle of shear and the width, dip, spacing and development history
of conjugate zones of shear-plus-dilation (fault zones) that define
wedges and grabens.