Recent Seabeam investigations over the East Pacific Rise in the northeast Pacific have shown the existence of a propagating spreading center at 18¿N. The propagating and dying spreading centers are joined by a zone of orthogonal lineations which appear to be the traces of a continuously migrating transform fault. Similar orthogonal lineations occur at 16¿N, 107¿30'W on the western side of the trace of a 5-m.y.-old propagating spreading center. The amplitude and the complexity of the topographic signature over the earlier propagating spreading center are higher and greater than over the presently active center, suggesting that the relief of the earlier center may owe its origin to differential subsidence of thermally contrasting segments of lithosphere, analogous to fracture zone topography of similar origin. Traces of former propagating spreading centers are thus a combination of two sets of landforms: those resulting from propagation and those resulting from the juxtaposition of two blocks of lithosphere of different thickness.