Constraints from GPS measurements on the dynamics of the zone of convergence between Arabia and Eurasia

We investigate the dynamics of deformation in the zone of convergence between the Arabian and Eurasian plates using a physical model that treats the lithosphere as a thin fluid sheet deforming in response to lateral variations in gravitational potential energy (GPE). This model has two free material parameters, the power law exponent, n, of the vertically averaged rheology of the lithosphere and the Argand number, Ar, which expresses the relative importance of GPE and stresses required to deform the lithosphere. With boundary conditions described by three additional free parameters, the model fits the observed deformation, as measured by 367 GPS velocities, with a root-mean-square residual of <2.4 mm/yr. We find negligible improvement when variations in material properties are introduced that represent increases or decreases in the lithospheric strength of the Central Iranian and Turkish-Iranian Plateaux and the Zagros Mountains. Effective viscosity of the lithosphere ranges from 5 × 1022 Pa s at 10 nanostrain/yr to 1022 Pa s at 100 nanostrain/yr. As well as matching the decadal time scale strain rates determined from GPS, the computed distribution of strain rates is also consistent with the distribution and types of earthquake focal mechanism. Significant historical earthquake activity is seen in regions with strain rates lower than 20 nanostrain/yr, implying that it is prudent to base assessments of seismic hazard on regional strain rates.