The Altyn Tagh fault slip rate paradox: New geodetic constraints and preliminary morphotectonic reconnaissance – The ATF paradox

The apparent discrepancy between geologic and geodetic estimates of slip rate on the Altyn Tagh fault (ATF) north of the Tibetan Plateau lies at the heart of the current debate about the mechanical response of the continental lithosphere to active continental collision; does Tibet deform as a system of quasi-rigid blocks with deformation confined to block boundaries, or does it deform in a more distributed fashion? - One of the keys to answer to this question would be to accurately estimate the slip rate of the central segment of the Altyn Tagh fault. However, no consensus has yet been reached, the geodesy suggests a rate of 5-17 mm/yr, and geological estimations range from 7 to 34 mm/yr. The kinematic boundary condition for Tibet (given by the Indian plate motion relative to the Tarim) suggests that 30-35 mm/yr of strike-slip are accommodated within the Tibet. If the central Tibet is a quasi-rigid block and the Altyn Tagh fault is the only active tectonic structure, then the Altyn Tagh fault slip rate could average 30-35 mm/yr. - Seismicity, heat flow and elastic flexure suggest a rheological structure of the Tibet really different from the surrounding India and Tarim region. This strong rheological asymmetry could introduce biases in the Altyn Tagh fault slip rate geodetic estimation that could only be corrected by extending the GPS measurements ~600 km south of the fault. This proposal is specifically aimed at determining the interseismic velocity field across the central Altyn Tagh fault by implementing an extended GPS profile (600-800 km) across the Altyn Tagh fault. A careful morphotectonics analyze and field geology will be conducted in the same time in this still unexplored region to check whether there are other active faults or not along the profile and to collect as many information as possible on the structure and composition of the crust. InSAR data will be processed along the GPS profile to densify and extend laterally the interseismic GPS measurements, and to look for postseismic transient along the profile, and apply a correction to the GPS motions if needed. ...