Dynamics of the Pacific-North American plate boundary in the western United States

The vertically averaged deviatoric stress tensor field within the western U nited States was determined with topographic data, geoid data, recent globa l positioning system observations, and strain rate magnitudes and styles fr om Quaternary faults. Gravitational potential energy differences control th e large fault-normal compression on the California coast. Deformation in th e Basin and Range is driven, in part, by gravitational potential energy dif ferences, but extension directions there are modified by plate interaction stresses, The California shear zone has relatively low vertically averaged viscosity of about 10(21) pascal seconds, whereas the Basin and Range has a higher vertically averaged viscosity of 10(22) pascal seconds.