The dilatancy-fluid diffusion model of the earthquake mechanism implies deformation of the epicentral area. Based on a result in the theory of thermoelasticity, we present a method for computing such deformation. Details are given for a dilating sphere and a dilating infinite cylinder buried in an elastic half-space. Given the volumetric strain of the dilatant region, the deformation measurements could be used to estimate the magnitude of the impending earthquake. Alternatively, a constraint on the volumetric strain can be obtained from deformation measurements before earthquakes that are preceded by dilatancy.