Expression of E-W fractures in magnetic surveys in parts of the U.S.A

Continental magnetic anomaly patterns are interrupted by east-west features similar to those found in the East Pacific. Distribution of these east-west interruptions in aeromagnetic surveys of parts of the United States has been analyzed quantitatively. Evidence of persistence of E-W interruptions across individual surveys for distances of more than 100 miles is presented. The Mendocino feature of the East Pacific can be traced through surveys in California to eastern Nevada, and possibly to eastern Colorado. By analogy with the East Pacific studies, magnetic features are interpreted as expressions of a pattern of fractures. There is no evidence of consistent offset comparable with that in the East Pacific. Fractures are considered to be deep and partly decoupled from the upper crust, so that they are clearly recognized in thin oceanic crust but are partly masked by shallow complexities in continental crust.