A Breakdown Zone Model of a Fault in a Strip

Abstract

A breakdown zone model for a fault of length a on y=0 is constructed in a strip of width 2H, based on two-dimensional elasticity theory. The three-dimensional concept from which this model is derived consists in that a strike slip fault exists in a thin brittle regime overlying a ductile regime or asthenosphere, and that outside of the strip in the brittle regime stresses or displacements will be changed little in the formation of a new shear crack surface. Two types of boundary condition are considered in an idealized form, i.e., zero stress change and zero displacement change on the boundary y=±H. To obtain the stress intensity factor for a semi-infinite crack in a strip, numerical methods are developed for solving integral equations. The results show that the critical shear stress against the ratio a/H for the critical state of fault formation separates in two branches at the point a/H=0, according to those two types of boundary condition.
What is relevant to our three-dimensional concept of a strike slip fault lies between the two cases. Then an expression for the critical shear stress is suggested, to a first approximation, independent of a/H. This is the same with the formula for an ordinary breakdown zone model in a homogeneous infinite medium. Since in our case, however, material constants are taken in the strip, our model may serve as a breakdown zone model of a strike slip fault related to a structural weak line in the crust.