The Mid-Atlantic Ridge: structure at 45° N

Summary. A structural model of the Mid-Atlantic Ridge at 45° N is proposed on the basis of travel-time data, amplitudes and synthetic seismograms. The crustal structure seems to be similar to that in the FAMOUS area (Fowler). At the ridge axis there is an absorptive zone in the upper mantle, the depth below the seabed to the top of this zone being about 6 km. Away from the ridge axis there is a positive velocity gradient of about 0.04 to 0.05 km/(skm) in the top 5 to 8 km of the upper mantle. Shear waves propagate across the ridge axis, suggesting that there is no sizeable crustal magma chamber. The shear-wave velocity of the uppermost mantle is 4.35 km/s.