We present the results of a seismic survey performed around the Kolbeinsey Ridge, North Atlantic. The seismic data were acquired along three profiles: on the ridge axis (L1), 12 km off-ridge (L2), and perpendicular to the ridge axis (L3). The models indicate lower velocity beneath the ridge axis than in the off-ridge area. Along L3, we obtain velocities of 2.6--3.6 km/s (upper crust), 4.8--6.0 km/s (middle crust), and 6.6--6.9 km/s (lower crust) beneath the ridge axis, while at more than 12 km off-ridge, the model shows velocities of 3.6--4.6 km/s (upper crust), 5.6--6.4 km/s (middle crust), and 6.9--7.2 km/s (lower crust). The model of L1 also shows significant lateral variation along the axis in the lower crust. The velocity in the lower crust decreases to 6.3 km/s in the southwestern part of L1, where the Moho depth decreases to 7.2 km. The low-velocity structure beneath the ridge axis is interpreted to be due to high porosity in the upper crust and to higher temperatures, as well as a few percent porosity, in the middle and lower crustal material. According to this interpretation, the crustal model of L3 implies that the cracks have been sealed and the temperatures have decreased to normal in 1.2-m.y-old crust. The anomalous low velocity structure along L1 can be interpreted as related to the most recent injection processes or a thermal influence of the Spar Fracture Zone situated 50 km south of the profile.¿ 1997 American Geophysical Union