Present‐day crustal motion within the Tibetan Plateau inferred from GPS measurements

Abstract

[1] Using the measurements of $726 GPS stations around the Tibetan Plateau, we determine the rigid rotation of the entire plateau in a Eurasia-fixed reference frame which can be best described by an Euler vector of (24.38°± 0.42°N, 102.37°± 0.42°E, 0.7096°± 0.0206°/Ma). The rigid rotational component accommodates at least 50% of the northeastward thrust from India and dominates the eastward extrusion of the northern plateau. After removing the rigid rotation to highlight the interior deformation within the plateau, we find that the most remarkable interior deformation of the plateau is a ''glacier-like flow'' zone which starts at somewhere between the middle and western plateau, goes clockwise around the Eastern Himalayan Syntaxis (EHS), and ends at the southeast corner of the plateau with a fan-like front. The deformation feature of the southern plateau, especially the emergence of the flow zone could be attributed to an eastward escape of highly plastic upper crustal material driven by a lower crust viscous channel flow generated by lateral compression and gravitational buoyancy at the later developmental stage of the plateau. The first-order feature of crustal deformation of the northeastern plateau can be well explained by a three-dimensional elastic half-space dislocation model with rates of dislocation segments comparable to the ones from geological observations. In the eastern plateau, although GPS data show no significant convergence between the eastern margin of the plateau and the Sichuan Basin, a small but significant compressional strain rate component of $10.5 ± 2.8 nstrain/yr exists in a relatively narrow region around the eastern margin. In addition, a large part of the eastern plateau, northeast of the EHS, is not undergoing shortening along the northeastward convergence direction of the EHS but is stretching.

Crustal–lithospheric structure and continental extrusion of Tibet

“…The GPS motions in Yunnan and Burma (Fig. 6) are also surprising, being almost at right angles to the strike-slip fault motions along the active dextral parts of the Red River Fault and the active dextral Sagaing Fault (Gan et al 2007).…”

“…6. GPS velocities across Tibet relative to a stable Eurasia, after Gan et al (2007). Contour lines indicate smoothed surface elevations using a 200 km wide Gaussian filter.…”

“…The latest GPS measurements from Gan et al (2007) consist of c. 726 stations around the plateau occupied during 1998-2004. Overall, the present-day GPS rates show north-south shortening of 40 mm a À1 across the plateau with almost 20 mm a À1 eastwest motion with respect to India and stable Asia (Fig.…”

“…They are either used to directly calculate a rate based upon a profile across the fault (Bendick et al 2000) or used in larger plateau-wide studies Gan et al 2007). Additionally, they are used in block or continuum models for the plateau (e.g.…”

“…Zhang et al 2004;Gan et al 2007), and are determined from fitting the horizontal velocities to a locked fault elastic model. The first GPS measurement for the Altyn Tagh was made by Bendick et al (2000) and consisted of a transect of GPS observations on the east-central portion of the fault and the North Altyn Tagh Fault.…”