Estimates of Permanent Strain Rates In the Western US

Understanding large-scale continental deformation requires separating permanent deformation from elastic strain that arises from frictional interactions of crustal faults. We invert GPS velocities, fault slip rates and earthquake slip vectors to estimate the long-term rotations of crustal blocks, frictional locking on crustal faults and strain rates within the blocks in order to reveal the strain sources in the western US from Mexico to Canada. We find that most of the modern strain is localized along known, active faults and that the slip rates on those faults are consistent with geologic estimates. South of the Mendocino Triple Junction northwest-oriented permanent shear strain dominates but to the north, where large elastic strains are observed, clockwise rotations of relatively coherent blocks take up most of the motion of the Cascadia forearc relative to North America.