The influence of the lithospheric thickness on bilateral slip

SUMMARY A 2-D model of slip formation and dynamic propagation in an elastic lithospheric plate, coupled to the asthenosphere and having a fault plane, is investigated using a finite element method. Slip is nucleated at a weak portion of the fault plane and propagates bilaterally. At the edges, slip is assumed to develop according to a critical shear stress criterion combined with a slip weakening law. Except for the weak portion, the slip resistance is constant along the fault plane. The influence of resistive stresses from the asthenosphere at the bottom of the plate is taken into account. The results indicate that bilateral slip lengths are limited to about the lithospheric plate thickness or somewhat larger. Such lengths will only be reached for sufficiently high tectonic loading. After maximum slip length has been reached, the slipping region is split into two regions of unidirectional slip, moving in opposite directions. The results thus illustrate one mechanism which limits the maximum amount of slip during an earthquake even in the absence of strong barriers.