Résumé
Creeping dislocations in an elastic half-space are commonly used to model interseismic deformation. However, this semi-infinite conventional model can lead to biased inferences of the slip rate and the fault locking depth. We therefore favor the use of a thin-plate model sheared at its base in agreement with the current knowledge of the seismogenic thickness of the lithosphere. We apply these two approaches to interpret InSAR data across the Altyn Tagh fault system near longitude 94 degrees E, in a region of clear asymmetry of interseismic velocity distribution. Our results suggest a locking depth of 7 - 9 km and a present-day geodetic slip rate of 8 - 10 mm/yr, consistent with the rate based on GPS measurements at this longitude. We interpret the asymmetric pattern as the joint effect of a rigidity decrease from the Tarim basin north of the fault to the Qaidam basin south of it and of a 5 - 7 km southward offset of strain concentration from the quaternary northern active fault. This suggests that the rigidity contrast as well as most of the creep at depth occurs on the southern geological fault.