A long reversed refraction line on the southeast flank of Reykjanes Ridge subparallel to the axis is modeled with synthetic seismograms. These are calculated using the reflectivity method. The data have been recorded by two bottom seismometers during the Reykjanes Ridge Iceland Seismic Program 1977 (RRISP77 experiment). The observed amplitudes are characterized by a low at around 80-km range and a pronounced maximum at around 100-km distance. Here the apparent velocity increases from about 8 km/s to at least 8.6 km/s in both directions. The modeling demonstrates that most of the observed features can be described by a laterally homogeneous structure except for layer 2 which thickens markedly toward Iceland. The structure of the lower crust seems to be similar to that of the Bay-of-Islands ophiolite, Newfoundland. There is an indication of a low-velocity zone at the base of the crust which may be caused by partial serpentinization of the olivine component of the gabbros at that depth. The Moho seems to be modeled best by a discontinuity about 10 km below the water surface. In the uppermost mantle there is a very slight velocity increase from 8 to 8.25 km/s. It is underlain by a transition zone to velocities as high as 8.6-8.9 km/s at about 20 km depth. This could possibly be explained by velocity anisotropy, perhaps together with a petrological boundary. The direction of maximum velocity of the deep anisotropic layer should be parallel to the ridge axis. This could be caused by a pipe flow from the Iceland mantle plume which is possibly indicated by the shear wave structure at greater depth.