The far-field contribution of the wavefield diffracted by topographical heterogeneities located in the vicinity of sources is analyzed in the case of nuclear explosions detonated inside the Taourirt Tan Afella massif, Algeria. The far-field scattered field is strongly shaped by the geometry of the topography and by the source location inside the mountain. Focusing and defocusing of the pP wave are shown. Back-scattering inside of the massif appears in the coda of the pP phase. For specific take-off angles, ie for given teleseismic distances, broadening of the pS diffracted field may appear. This broadening is explained by the simultaneous arrival of the pS and the P surface wave to S converted wave, with similar polarizations. ¿ 1997 American Geophysical Union