Chapter 2

Strange undersea faults


Tuzo WilsonTuzo WilsonJohn Tuzo Wilson (1908-1993) worked at Princeton and was the first to suggest that island chains such as Hawaii arose as plates moved across a hot spot in the mantle below. In the early 1960s, maps of the magnetic anomalies on the ocean floor showed symmetrical patterns at mid ocean ridges, cut by discontinuities. With simple paper models, starting from Vine and Matthews’ work, Wilson suggested that transform faults were not later faults affecting ridges, but rather essential parts of the ridge system. Lynn Sykes at Lamont showed that earthquake motions along the faults matched Wilson’s model, and that transform faults away from the ridges were inactive. worked out the geometry of the long straight faults seen on the seafloor from their offset of the magnetic anomalies. He saw these transform faults as integral parts of the plate boundary. The faults offset the straight ridge segments to allow for the curvature of the Earth; they are part of the ridge and are active only in the region between one active ridge segment and another; away from the ridge the faults are frozen into the seafloor. As a result the juxtaposition of the 1000 kilometre offsets and the continental margin is not the enigma it had appeared to be.

IMAGE REFERENCE: Figure from: Wilson (1965) ‘Transform faults, oceanic ridges’ Science. 150(3695): 482-485.