The elastic problem of a shear-loaded asperity on an infinite fault plane is studied based on a linear perturbation approach developed by Rice (1985). The fault plane is broken everywhere except at an asperity whose shape differs modestly from a circle. The stress concentration along the bounding edge of the asperity due to remotely applied displacements and/or forces is analyzed in terms of in-plane shear mode stress intensity factor K2 and antiplane shear intensity factor K3. The asperity configuration corresponds to an external crack which is of importance in understanding the general shear mode fracture of elastic connections. Solutions by Fourier series are developed for asperities subjected to remotely applied displacements and forces. Assuming the fracture process on the fault plane is governed by the intensity of maximum shear stress concentration, we use the perturbation results to study the configurational stability of a circular asperity. It is found that the circular shape is configurationally stable when rigid rotations are fully suppressed at remote field, and the crack front is thus expected to remain circular during quasi-static growth. ¿ American Geophysical Union 1989