A three-dimensional spatial distribution of relative scattering coefficients is estimated for the Galeras volcano, Colombia, by an inversion of the coda wave envelopes from 1564 high quality seismic recordings at 31 stations of the Galeras seismograph network. The inversion reveals a highly non-uniform distribution of relative scattering coefficients in the region for the two analyzed frequency bands (4-8 and 8-12 Hz). Strong scatterers show frequency dependence, which is interpreted in terms of the scale of the heterogeneities producing scattering. Two zones of strong scattering are detected: the shallower one is located at a depth from 4 km to 8 km under the summit whereas the deeper one is imaged at a depth of ~37 km from the Earth's surface. Both zones may be associated with the magmatic plumbing system beneath Galeras volcano. The second strong scattering zone may be related to a deeper magma reservoir that feeds the system.