The nature of the Pamir subduction zone derived from stress field modelling

Abstract

In this thesis a new approach is tested to determine the nature of the subduction processes occurring in the Pamir orogen. The occurrence of subduction underneath the central Pamir Mountains, located on the eastern border of Afghanistan and Tajikistan, has been subject to discussion for more than three decades. Seismic imaging and earthquake data of the area have shown a slab up to a few hundred kilometres deep, but whether it is continental or oceanic material subducting has not yet been conclusively decided. In this thesis we construct a model of the stress field of the region as a consequence of long wavelength forces and the slab pull in the Pamir region. We test several slab pull scenarios corresponding to continental or oceanic subduction. The resulting stress fields are compared to stress observations to find whether including the subduction processes gives a better fit. We compare the instantaneous displacements associated with the applied tractions to the movement of the region as obtained through GPS. A range of scenarios is tested to account for geometry and material properties. Our preferred model is the model with a neutrally buoyant slab of Eurasian origin. This implies that active continental subduction is taking place in the Pamir mountains.