Earthquake-cycle deformation and fault slip rates in northern Tibet

Fault slip rate estimates along the Altyn Tagh and Kunlun strike-slip faults in northern Tibet vary considerably between short-term geodetic and long-term geologic studies. Here we reanalyze and model all global positioning system (GIPS) data from northern Tibet to determine if these differences might be explained by previously unmodeled transient processes associated with the earthquake cycle, which can bias slip-rate estimates from geodetic data. We find that these effects cannot reconcile the geodetic data with the lowest bounds on the geologic slip rates along these faults, even in the presence of low (< 10(18) Pa s) viscosities within the mid-crust or crust and mantle lithosphere. Surface velocities derived from GPS measurements are best reproduced with models with a high-viscosity (>= 10(18) Pa s) middle to lower crust and mantle lithosphere.