Kinematics and Dynamics of the Pamir, Central Asia: Quantifying the Roles of Continental Subduction in Force Balance

Abstract

An updated kinematic model constrained by GPS observations and fault slip rate information from the Central Asia Fault Database provides updated modeled slip rates for major faults in the Pamir. The kinematic model constrains thin sheet continuum mechanics models that distinguish the contributions of subducting continental lithosphere to force balance. Dynamic model sensitivity tests show that major features of the force balance results are insensitive to chosen lithospheric compensation style, integration depth, and inclusion of subducting low‐density continental lithosphere in the upper 100 km. Forward models incorporate deviatoric stresses associated with gravitational potential energy, velocity boundary conditions, and lateral strength variations. Differential strain rate fields, which represent residual forces not accounted for in the forward models, separate and quantify the deformation associated with the Pamir slab. The downward pull of foundering lithosphere augments compression along the Pamir Frontal Thrust System and shear along the eastern and western Pamir boundaries. North‐south extension in the residual differential strain rate field is spatially associated with Pamir gneiss domes and may be related to the interaction of the slab with the mantle. We do not find evidence for slab pull associated with a separate Hindu Kush slab.

Two kinematic transformations of the Pamir salient since the Mid-Cenozoic: Constraints from multi-timescale deformation analysis

“…On the decadal timescale, GPS measurements have shown that present-day ~N-S shortening rates across the PTS range from 10 to 15 mm/yr (Zubovich et al, 2010;Ischuk et al, 2013;Zhou et al, 2016). The rates are consistent with the modeling rates (11.8-14.4 mm/yr) from a kinematic model based on recent GPS velocities and Quaternary fault slip rates (Jay et al, 2017;Jay et al, 2018). The velocities from four GPS stations across one strand of the western PFT indicated a shortening rate of 2.2 ± 0.8 mm/yr and dextral-slip rate of 5.6 ± 0.8 mm/yr near the Altyndara River (Zubovich et al, 2016).…”

Role of Large‐Scale Tectonic Forces in Intraplate Earthquakes of Central and Eastern North America

“…We next calculate the deviatoric stresses arising from those GPE variations by solving the depth integrated (from a variable surface elevation to a reference depth of 100 km below the sea level) force-balance equations on a global grid with lateral viscosity variations, using the "thin sheet" approximation (Ghosh et al, 2006(Ghosh et al, , 2009. Earlier studies have shown that integrating to depths shallower or deeper than 100 km does not substantially affect the GPE differences and hence the associated deviatoric stresses (Ghosh et al, 2009;Hirschberg et al, 2018;Jay et al, 2018;Klein et al, 2009). The second step involves calculating deviatoric stresses associated with horizontal tractions acting at a specific reference depth (base of depth integration, 100 km below sea level), which are obtained from a global mantle circulation model driven by tomography and history of subduction (Wen & Anderson, 1997), along with lateral viscosity variations in the lithosphere (Ghosh et al, 2008;Ghosh & Holt, 2012).…”

Surface Motions and Continental Deformation in the Indian Plate and the India‐Eurasia Collision Zone

“…() and Jay et al. (). In the east, the Sagaing fault shows E‐W compression whereas dominantly N‐S compression is seen in the Bengal fan.…”

“…For a common reference level, we assume a depth of 100 km below sea level, but this depth can be varied. Integrating up to different depths will change the total GPE, but not the GPE differences and hence the associated deviatoric stresses will remain largely unaffected (Ghosh et al., ; Hirschberg et al., ; Jay et al., ; Klein et al., ). We calculate GPE using CRUST1.0 model (Laske et al., ) that gives the thickness and densities of various crustal layers on a 1° × 1° global grid.…”