The present invention relates to a harmonic seismic wave generator which continuously generates seismic waves with a single precisely defined frequency and amplitude and with a special radiation characteristic. The invention further relates to an assembly useful for seismic prospecting and a method of seismic prospecting. A signal generated by the generator propagates through the rock environment, is received by an array of the seismic stations and is processed in a way that detects and analyzes nonlinear phenomena in the propagation of seismic waves. The use of the generator allows, in particular, a detection of critical stress before an earthquake.