Abstract. Geological surfaces are generally known incompletely and have to be reconstructed by use of interpolation methods. Some of these surfaces may be described by a continuous function z = u ( x , y ) , where z is the vertical coordinate (depth). However, tectonic stresses cause discon tinuities (faults) and complicated surfaces (folds). In order to interpolate geological surfaces an algorithm is proposed which uses triangular finite elements. Among all functions satisfying the given constraints ( u and pos sibly u x and u y at the data points) the sought function shall minimize an integral, the potential energy of a thin elastic plate.