Magnetic variation anomalies and seismic low-velocity zone in the western United States

Two-dimensional conductivity models relating the seismic low-velocity zone in the upper mantle to a zone of enhanced electrical conductivity satisfy the observed anomalous magnetic variation fields in the western United States. The upper mantle structure of the Colorado Plateau is intermediate between that of the Basin and Range and southern Rockies provinces, characterized by a well-developed low-velocity zone and high electrical conductivity, and the structure of the Great Plains, where mantle conductivities are low and the low-velocity layer is thin.