Rayleigh waves generated from seismic events in southern Germany and recorded at the broad-band GRF array, have been analysed. The group velocities have been determined from 60 to 16 s along more than 100 carefully selected seismic paths. A regionalization method, based on the classical approach for surface wave propagation, has been applied to this data set. The lateral heterogeneities, inferred from the lateral variations of the group velocities after the 2-D inversion, present an excellent correlation with the known geological features. The effects on group velocities involved by these lateral heterogeneities may exceed¿10%. Azimuthal anisotropy might exist beneath the region in agreement with earlier results inferred from Pn-wave travel times. ¿American Geophysical Union 1991