GPS Determined Asymmetric Deformation Across Central Altyn Tagh Fault Reveals Rheological Structure of Northern Tibet. Issue 9 (20th September 2022)

• Record Type: Journal Article
• Authors: Ge, Wei‐Peng; Shen, Zheng‐Kang; Molnar, Peter; Wang, Min; Zhang, Pei‐Zhen; Yuan, Dao‐Yang
• Is Part Of: Journal of geophysical research. Volume 127:Issue 9(2022)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2022-09-20
• Subjects: Tibetan Plateau -- lithosphere -- rheology -- Altyn Tagh fault -- GPS -- deformation; Geomagnetism -- Periodicals; Geochemistry -- Periodicals; Geophysics -- Periodicals; Earth sciences -- Periodicals; 551.1
• DOI: 10.1029/2022JB024216
• Languages: English
• ISSNs: 2169-9313

Abstract

Abstract: 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 × 10 19 Pa s (between 3.5 and 9.1 × 10 19 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. Plain Language Summary: Markedly asymmetric interseismic deformation is observed across the Altyn Tagh fault, revealing differing lithospheric rheology across the fault between northern Tibet and the Tarim Basin. We invoke a 2‐dimensional viscoelastic deformation model to interpret the GPS velocity field across the central Altyn Tagh fault and find that the deformation field is well explained by viscoelastic deformation of the lower crust and upper mantle, underneath a thin elastic layer (∼17.5 km thick) for the northern Tibet and Qaidam Basin and a thick elastic layer (>60 km thick) for the Tarim Basin, respectively. The inferred effective viscosity of ∼5.1 × 10 19 Pa s for northern Tibet lithosphere substrate is similar to that beneath other regions with thin lithosphere in the world. Characterization of the rheological structure of the Tibetan plateau and its boundary faults helps understanding dynamic processes of the plateau lithosphere and the continental lithosphere at large. The estimated long‐term slip rate of ∼12 mm/yr for the central Altyn Tagh fault is ∼30% higher than the consensus estimate of previous geodetic studies, which has a significant implication for the assessment of seismic hazard for the northern rim of the Tibetan plateau. Key Points: Asymmetric interseismic deformation across Altyn Tagh fault reveals differing lithospheric rheology between northern Tibet and Tarim Viscosity of 5.1 ( +4.0 /–1.6 )×10 19 Pa s for lower crust and upper mantle of northern Tibet and Qaidam is similar to that beneath regions of thin lithosphere Effective elastic thickness of northern Tibet and western Qaidam Basin (16.5–20 km) is notably thinner than that of Tarim Basin (>60 km)