The vertically averaged deviatoric stress tensor field within the western United States was determined with topographic data, geoid data, recent global positioning system observations, and strain rate magnitudes and styles from Quaternary faults. Gravitational potential energy differences control the large fault-normal compression on the California coast. Deformation in the Basin and Range is driven, in part, by gravitational potential energy differences, 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.

We perform a joint inversion of Quaternary strain rates and 238 Global Positioning System (GPS) velocities in Asia for a self‐consistent velocity field. The reference frames for all geodetic velocity observations are determined in our inversion procedure. India (IN) moves relative to Eurasia (EU) about a pole of rotation at (29.78°N, 7.51°E, 0.353° Myr−1), which yields a velocity along the Himalaya within India that is ∼73–76% of the magnitude of the IN‐EU NUVEL‐1A velocity and a vector azimuth that is 8–10° clockwise of NUVEL‐1A IN‐EU vector azimuth. Relative to Eurasia, south China moves at 9–11 mm/yr in the direction 110–120° with a pole position (64.84°N, 156.74°E, 0.12° Myr−1). Amurian block motion has a pole position in a similar location but at a slower rate (64.61°N, 158.23°E, 0.077° Myr−1) and most of the Amurian‐Eurasia motion is accommodated by extension across Lake Baikal. Tarim Basin moves relative to Eurasia about a pole of rotation at (39.24°N, 98.2°E, −0.539° Myr−1) and ∼16–18 mm/yr of shortening is accommodated across the west central Tien Shan. There is distributed E‐W extension throughout both southern and north central Tibet. Within southern Tibet, between the longitudes of 77°E to 92°E, the deformation field accommodates ∼16–19 mm/yr of E‐W extension. We compare predicted seismic moment rates with those observed in this century in Asia. Total observed seismic moment rates within the entire area of central and east Asia (2.2×107 km2) in this century are 2.26±0.7×1020 N m yr−1 as compared with a predicted total rate of 2.03±0.066×1020 N m yr−1. Comparisons between observed and predicted moment rates within 42 subregions reflect the generally unstable process of inferring long‐term seismic moment rates from a catalog of limited duration (94 years). An observation period of ∼10,000 years would be required to reduce uncertainties in observed seismic moment rate to the same size as the uncertainties in model tectonic moment rates, inferred from the joint inversion of GPS and Quaternary rates of strain. We show that in general, a better correlation with model tectonic moment rate is inferred from the seismicity catalog by considering the numbers of earthquakes above a cutoff magnitude (mb ≥ 5.0, for the period January 1, 1965, to January 1, 1999).

S U M M A R YWe investigate the forces involved in driving long-term large-scale continental deformation in western North America, and quantify the vertically averaged deviatoric stress field arising from internal buoyancy forces and the accommodation of relative plate motions. In addition, we investigate the ability of regional models to resolve the level of tractions acting at the base of the lithosphere. We directly solve force-balance equations for vertically averaged deviatoric stresses associated with differences in values of 1/(lithospheric thickness) times the gravitational potential energy per unit area (GPE). The GPE values are inferred using both the ETOPO5 topographic data set and the CRUST2.0 crustal thickness model. Deviatoric stresses associated with basal tractions are calculated globally, with inputs determined from an isoviscous upper mantle (η = 10 21 Pa s) 3-D large-scale convection model in which mantle density variations were inferred from tomographic data and the history of subduction. In a 211-parameter iterative inversion we then solve for a stress field boundary condition by fitting stress field indicators (i.e. the directions and relative magnitudes of the principal axes of kinematic strain rates). Magnitudes of the total vertically averaged deviatoric stress field (sum of GPE solution with the boundary condition solution) range from 5 to 10 MPa within a 100-km thick lithosphere. These magnitudes are calibrated by the GPE differences, along with the spatial variation in deformation style. There is a trade-off between the scaling of the basal traction deviatoric stress field and the boundary condition solution. However, the combined boundary conditions plus basal traction solution is robust (in both magnitude and style), and when added to the contribution from GPE differences provides a global minimum of misfit between the total deviatoric stress solution and the stress field indicators. GPE variations account for ∼50 per cent of the deviatoric stress magnitudes driving deformation, while boundary condition stresses account for the remaining ∼50 per cent of deviatoric stress magnitude. By comparing possible end-member strength profiles with our vertically averaged deviatoric stresses we infer that the bulk of the strength within the lithosphere in western North America lies within the brittle seismogenic layer.

Abstract. The western margin of the Indian plate is highly oblique to the direction of convergence between India and Asia and represents an excellent example of large-scale oblique continent-continent collision. Determining the strain field in western Pakistan and how it relates to the plate motion and plate margin geometry affords an exceptional opportunity for understanding oblique margin processes in general. Through the inversion of regional and teleseismic body waves, we have determined the source parameters of 10 moderate-sized earthquakes that occurred between 1964 and 1985 in and around the Sulaiman Range, Pakistan. The earthquakes are dominantly thrust events with slip vectors that are approximately perpendicular to the lobate Sulaiman mountain front. Slip vector orientations rotate 600-70 ø from a N-S to a WNW-ESE direction of compression, consistent with the geometries of the complex, festoon-shaped mountain belts of this margin. We have estimated the spatial variation of the horizontal strain rate and velocity fields within Sulaiman using vertically averaged models that accommodate plate motion constraints within a deforming layer. The most important factors determining the style of strain rotation in the Sulaiman Lobe and Range are the presence of pure strike-slip motion along the Chaman Fault, and the relatively rigid and undeformed Katawaz Basin that is therefore allowed to translate obliquely relative to India. This same conclusion is obtained using either a three-dimensional, frictional, analogue model with significant basal tractions or a thin sheet viscous numerical model without basal tractions. Thrusting in a predominantly NW-SE direction in the Sulaiman Range accommodates 5-14 mm/yr of N-S motion between India-Eurasia and 3-6 mm/yr of E-W shortening. Seismic moment release this century within the India-Eurasia plate boundary zone, west of the western Himalayan Syntaxis, constitutes roughly 40% of the expected total seismic moment release l•br this time period. Particularly significant moment rate deficits exist within the Sulaiman Range and along the Chaman Fault.