We estimate the moment magnitudes of microseismic events by fitting theoretical models to the amplitude spectra of the corresponding recorded signals. To this end, we combine the available information by stacking the seismic traces that contain the event and use Very Fast Simulated Annealing (VFSA) to solve the optimization problem. We test the procedure on pseudo-synthetic and real data considering the same optimization problem with different sets of unknowns. In addition, we evaluate the relative errors that the corresponding solutions generate on the final moment magnitude value.Facultad de Ciencias Astronómicas y Geofísicas