We have applied a dislocation model, consisting of a dipping tabular body with constant dislocation perpendicular to the plane of the body, to surface displacements related to an intrusion in the south flank of Etna volcano, Sicily. Ground deformation was measured by a trilateration array and automatic tilt measurements during the 1989 eruption of the volcano. Significant line length changes and tilt were measured associated with an episodic 0.8 km propagation of the intrusion into the measurement array. We incorporated the orientation and location of measured surface cracking into a Bayesian nonlinear inversion of the data to determine the geometry of the intrusion. We suggest the intrusion caused a 1-m-wide opening of a vertical crack that extended from a depth of 1 km to within a few hundred meters of the surface. We relate the distribution of surface cracking and seismicity associated with the fracture to stresses generated in the slip-weakening zone associated with the crack edge. ¿ American Geophysical Union 1993