(b) Slip along a border fault produces a topographic depression which is controlled by the heave, E, across the fault and the shape of the detachment (here drawn listric soling into the base of the crust). This depression is produced by the collapse of the hanging wall block, which juxtaposes cool hanging wall material onto hotter footwall material. Both the simple shear and plastic deformation raise the lithosphere/asthenosphere boundary and hence introduce heat to the base of the lithosphere. Because extension through the lithosphere must be balanced (but not necessarily locally), the integrated plastic deformation must equal the total heave across the detachment fault. The final width of the extended region is L. The offset between these two distributions is defined by offset. Delta is the crustal or upper plate extension factor and beta is the lithospheric mantle or lower plate thinning factor.

(c) Flexural adjustment of the lithosphere in response to crustal unloading and input of heat to the base of the lithosphere. The resultant shape of the rift basin is given by the summation of the kinematic depression and the total flexural rebound of the lithosphere.