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

Abstract

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.

Crustal Deformation in the India‐Eurasia Collision Zone From 25 Years of GPS Measurements

“…Second, there can be regions where there are no forces acting to cause deformation—a region may not be strong but nevertheless will only deform if it is subjected to appropriate forces. This has been proposed as a mechanism to explain low‐strain regions in the central Iranian and Turkish‐Iranian plateaux (Walters et al, ). The presence of low‐strain regions is therefore not a useful feature for discriminating between block and continuum models.…”

New perspectives on ‘geological strain rates’ calculated from both naturally deformed and actively deforming rocks

“…Some thin viscous sheet studies report large lateral variations in rheological properties, for example, larger viscosities associated with semirigid microplates and lower values in rapidly deforming areas (Flesch et al, 2000(Flesch et al, , 2001. In other studies, however, such variations result in a negligible reduction in misfit compared to homogeneous models (England and Molnar, 2015;Walters et al, 2017).…”

Initiation of Clockwise Rotation and Eastward Transport of Southeastern Tibet Inferred from Deflected Fault Traces and GPS Observations

“…The reliance on just two dimensionless numbers allows their ranges of values to be explored, and for their roles in large scale deformation to be revealed and assessed (e.g., England and Houseman, 1986;Houseman and England, 1986). Comparisons of large-scale deformation from essentially all regions of large-scale deformation show patterns of deformation that can be matched by treating the continental lithosphere as a thin viscous sheet: eastern Asia (England and Houseman, 1986;England and Molnar, 1997;Flesch et al, 2001;Holt and Haines, 1993;Holt et al, 1991); Iran (Walters et al, 2017); Anatolia (England et al, 2016), and western North America (Bahadori et al, 2018;Flesch et al, 2000;Reitman and Molnar, 2021;Whitehouse et al, 2005). Moreover, strain-rate fields measured at the surface using GPS match those implied by seismic anisotropy in the underlying mantle, which suggests vertically coherent deformation through the lithosphere (e.g., Chang et al, 2015;Davis et al, 1997;Flesch et al, 2005;Holt, 2000).…”