Significance The Songpan-Ganzi terrane lies in the central-east of the Tibetan Plateau, which was considered a stable block in some tectonic models. Its deformation mode is of crucial importance for understanding the evolutionary history and seismic hazard of the plateau. The recent Maduo earthquake occurred inside the terrane. We resolve a bilateral rupture process with distinct super- and subshear rupture modes for this event. We also find that pervasive folding structures that are aligned by shear deformation in the current Songpan-Ganzi terrane are responsible for the seismic wave anisotropy and shear strain orientation in its upper crust. Its deformation mode can be classified as distributed simple shear, which receives shear loads from side walls and produces internal earthquakes.

We establish a continuous GPS transect crossing the central Altyn Tagh fault at 90°E with eight years of observations. GPS velocities along this profile and another one crossing the fault at 86°E suggest a fault slip rate of 12.4 ± 0.7 mm/yr, but with asymmetric straining of adjacent terrain. On the south side, ∼8.2 mm/yr of left‐lateral shear is absorbed across a region ∼210 km from the fault, but only ∼4.2 mm/yr is found on the north side. This estimate of slip rate is ∼30% larger than the consensus estimate of previous models. By treating the deforming regions as elastic plates with different thicknesses overlying a substrata that obeys a linear Maxwell viscoelastic constitutive relationship, we infer a viscosity of ∼5.1 × 1019 Pa s (between 3.5 and 9.1 × 1019 Pa s at 1‐σ) on the south side, beneath northern Tibetan Plateau. This low viscosity, compared to some estimates for the asthenosphere, concurs with the Tibetan Plateau being underlain by a relatively hot and weak lower crust and upper mantle. The effective elastic thickness on the south side is 16.5–20 km, which is significantly smaller than that of the Tarim Basin of >60 km.