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Stylized model of the upper crustal velocity structure along profile A.

This model gives us a more immediate impression of the rift profile, partly because of its triple vertical exaggeration. Note the fault lines; of course, the borders of the deep portion, i.e. the central rift itself, also are bordered by faults, that's the very definition of a rift. Unlike the previous image based on reflection data, this model was constructed from seismic refraction data which measure the velocity of sound waves inside formations. More about this.htmlect of seismic measurements later on.
Other geophysical methods also can give us impressive signatures of the Keweenawan rift valley. Just take a look at the gravity picture over Lake Superior.

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