SUMMARYThe heat extraction through a geothermal reservoir on an oblique fault plane in the earth's crust is considered. The fault could be modelled mechanically as a frictional contact interface of two elastic bodies. The heat is recovered by circulating fluid through the reservoir, and then the surface of the reservoir is cooled by the fluid. The analysis is based on the two-dimensional theory of quasi-static thermoelasticity. It is concluded from numerical calculations that a geothermal reservoir can be created on an oblique fault plane, and the opened region, i.e. the fluid-filled region, increases gradually with time during the heat extraction. Also discussed are the effects of the fluid pressure and the coeficient of friction on the behaviour of the reservoir.