Tectonic interaction between the Pamir and Tien Shan observed by GPS

Abstract

The complex tectonic interplay between the Central Asian Southwest Tien Shan and the north advancing Pamir as well as the role of the Pamir Frontal Thrust (PFT) separating these two orogens along the intervening Alai Valley is yet unclear. In this paper we present data of the newly installed Western Alai GPS profile (WAGP), capturing the deformation signal of both mountain ranges. The 20 km long WAGP records a maximum displacement rate of 9.3 ± 0.8 mm yr À1 . The lion's share of displacement (6.0 ± 0.8 mm yr À1) is accommodated between the two stations located directly north and south of the PFT in 5 km distance. The WAGP data nicely complement the existing South Tien Shan and the Pamir GPS network data, which we present here in a combined reference frame and use it as input for horizontal block rotation/strain models. The model results show that both the Southwest Tien Shan and the Pamir behave as uniformly strained blocks and rotate counterclockwise (with respect to Eurasia) by 0.93 ± 0.11°Myr À1 and 0.62 ± 0.05°Myr À1 , respectively. The Southwest Tien Shan undergoes NNE-SSW shortening of À22.1 ± 1.5 × 10 À9 year À1 with an insignificant perpendicular extension. The Pamir is shortening with a rate of À10.2 ± 3.8 × 10 À9 year À1in a NNE-SSW direction, which is nearly 2.5 times less than its lateral extension rate. A band of increased deformation along the PFT is bounded to the north by the northern rim of the Alai Valley and extends up to 30-50 km south into the Pamir.

Kinematics and dynamics of the Pamir, Central Asia: Quantifying surface deformation and force balance in an intracontinental subduction zone

“…Velocities do not rotate along the eastern margin of the Pamir; there, the Pamir and the Tarim basin appear to move northward together as suggested by Sobel et al [], Ischuk et al [], and Thompson et al []. Velocities change abruptly across the PFTS, indicating significant strain localization there (Figure b) [ Zubovich et al , , ].…”

“…This agrees with Flesch et al [] and Ghosh et al [], who found that stresses associated with both GPE and boundary conditions explain deformation in the India‐Eurasia collision zone. Since the stress field boundary conditions indicate no east‐west tension, gravitational collapse accounts for all east‐west extension in the deformation field [ Burtman , ; Stübner et al , , ; Schurr et al , ; Zubovich et al , ; Rutte et al , , ]. India‐Eurasia convergence explains the north‐south compression that dominates the stress field boundary conditions, but it cannot explain the rotation of principal deviatoric stress axes near the PFTS.…”

“…The present‐day Pamir is bounded to the north by the Tien Shan mountains, to the south by India, to the east by the rigid Tarim basin, and to the west by the Hindu Kush mountains and Tajik basin (Figure a). To the north, the PFTS localizes deformation as the Pamir moves northward with respect to the Tien Shan, progressively closing a narrow intramontane basin called the Alai valley [ Arrowsmith and Strecker , ; Coutand et al , ; Zubovich et al , ]. In this paper, the PFTS includes the Main Pamir Thrust and Pamir Frontal Thrust (Figure b), which root in the same décollement [e.g., Li et al , ; Sobel et al , ; Thompson et al , ].…”

Seismic Anisotropy Beneath the Pamir and the Hindu Kush: Evidence for Contributions From Crust, Mantle Lithosphere, and Asthenosphere

“…During this northward movement, the Pamir crust was intensely shortened, and the once connected Tajik and Tarim basins were separated (Figure a). GPS measurements show that the rate of crustal shortening across the Pamir Thrust System, the present deformation front between the Pamir and the Tian Shan, is around 10–15 mm/year (Ischuk et al, ; Zubovich et al, , ). Pamir crust also extrudes westward into the Tajik basin forming a foreland fold and thrust belt, which is restricted to the north by the transpressional Illiac Fault zone.…”

The 2015 Mw7.2 Sarez Strike‐Slip Earthquake in the Pamir Interior: Response to the Underthrusting of India's Western Promontory

“…The region is seismically active producing magnitude >6 earthquakes approximately every 10 years. Over the last 50 years, those occurred mainly along the Pamir's northern perimeter, the Pamir thrust system, which accommodates 13–19 mm/yr of the India‐Asia convergence (Ischuk et al, ; Zubovich et al, , ). The Pamir interior is seismically less active, both in long‐term global earthquake catalogs (Storchak et al, ) and observed by a dense local seismic network (Schurr et al, ).…”