Tectonic highlights of the recent deformation field of the Pamir, the Tajik basin, and the Hindu Kush, observed by high-resolution satellite-geodesy

At the northwestern tip of the India-Asia collision zone, the north-advancing Pamir orocline overrides the Tajik-Tarim Basin along a low-angle décollement with N–S shortening rates of 10-15 mm/yr. The Pamir’s advance is buttressed in the North by the Tian Shan. Westward collapse of Pamir crust into the Tajik basin leads to overall E–W shortening in the ~N-trending Tajik fold-thrust-belt. Crustal seismicity highlights fault systems at the northern rim of the Pamir and, since the 2017 M_w7.2 Sarez earthquake, the Sarez-Karakul fault system that separates the western from the eastern Pamir as a surface expression of the northwestern tip of the underthrusting Indian cratonic mantle lithosphere. Towards southwest, the Pamir connects to the rarely sampled Hindu Kush with sparse crustal but abundant intermediate-depth seismicity; the latter is an effect on an ongoing slab break-off.

We recorded displacements along the most active structures creating the recent regional deformation field by multiple satellite-geodetic observations. Up to 4.5-yr-long radar-interferometric time-series (InSAR) provide E–W and vertical surface deformation fields in unprecedented spatio-temporal resolution of 400 m and 12-24 days. The relative InSAR rate maps were tied to and complemented with accurate rates derived from Global Navigation Satellite System (GNSS) data. We collected these data in continuous and survey mode along—sometimes km-spaced—profiles across the most active faults in the region.

We confirm the high interseismic strain localization along the Pamir’s northern thrust front and an increased dextral component towards the northwestern edge of the thrust belt of >8 mm/yr, accommodating the westward collapse of the orocline. The sinistral Sarez earthquake at 120-170 km distance from the front activated the basal décollement, as suggested by mm-to-cm-scale, sharp surface offsets along the whole frontal segment. Relocking occurred gradually in the following four years. Similar co-seismic offsets were observed along the sinistral, NE-trending Darvaz fault, separating the western Pamir from the Tajik basin. The Tajik fold-thrust-belt exhibits ~10 mm/yr of internal E–W shortening, in agreement with fossil shortening rates of 12-8 mm/yr since ~12 Ma. The majority of the deformation is accommodated by the Babadag backthrust (~6 mm/yr)—a major thrust located far west in the belt, and the sinistral Ilyak fault (~6 mm/yr) that bounds the belt to the North. The belt also hosts spectacular horizontal spreading rates of ≤350 mm/yr at the Hoja Mumin salt fountain. Along the most prominent fault of the Hindu Kush, the Panjsheer fault, a fault-perpendicular GNSS profile observed sinistral slip of >1-4 mm/yr. The fault is probably only locked in the upper ~km as suggested by a sharp, InSAR line-of-sight rate increase of ~6 mm/yr across the fault. This could explain the absence of shallow seismicity in the region.