The N-S direction strike-slip activities in the Pamir hinterland under oblique convergence: the 2015 and 2023 earthquakes

Summary The prominent Pamir plateau holds considerable significance in comprehending the processes of Asian continental collisional orogeny. However, due to harsh natural conditions and low seismic activity within the Pamir hinterland, our understanding of this region remains deficient. Recent major events and the accumulation of geodetic observations present a rare opportunity for us to get insights into the tectonic activities and orogenic processes occurring in this region. Firstly, employing Sentinel-1 and ALOS-2 SAR images, we acquire coseismic displacements associated with the most recent earthquakes in 2015 and 2023. Subsequently, we conduct the souce models inversion with the constraints of surface displacements based on a finite-fault model. Our results reveal displacements ranging from -0.8 m to 0.8 m for the 2015 Mw 7.2 Tajik earthquake and -0.25 m to 0.25 m for the 2023 Mw 6.9 Murghob event, respectively. The optimal three-segment model for the 2015 event ruptured a fault length of 89 km with a surface rupture extending 59 km along the Sarez-Karakul fault (SKF), characterized predominantly by left-lateral strike-slip motion, with a maximum slip of 3.5 m. Meanwhile, our preferred uniform slip model suggests that the 2023 event ruptured an unmapped fault in the southern Pamir region with a strike angle of 31° and a dip angle of 76.8°. The distributed slip model indicates that the 2023 event ruptured a fault length of 32 km, resulting in an 8 km surface rupture. This event is characterized by left-lateral strike slip, with a peak slip of 2.2 m. Secondly, the Coulomb stress calculations demonstrate that the 2023 event was impeded by the 2015 event. Finally, interseismic GPS data reveals a relative motion of 3.4–5.7 mm/yr in the N-S component and 3.2–3.8 mm/yr in the E-W component along the SKF in the Pamir hinterland, respectively. These N-S direction strike-slip activities and slip behaviors support an ongoing strong shear and extension in the Pamir regime, which is a response to the oblique convergence between the Indian and Eurasian plates.