Early Postseismic Deformation of the 2010 Mw 6.9 Yushu Earthquake and Its Implication for Lithospheric Rheological Properties

We used the 250-day postseismic displacements derived from Global Positioning System data to explore various postseismic deformation processes of the 14 April 2010 Mw 6.9 Yushu earthquake, including the afterslip of the fault, viscoelastic relaxation in the lower crust and upper mantle, and the poroelastic rebound. The preferred model shows that the afterslip of the fault decays rapidly with time. Viscoelastic relaxation in the lower crust and upper mantle decays slower with time but affects a broader area. Our results show that the range of the steady-state viscosity in the lower crust is 0.3-2 x $\times $ 10(19) Pa s. The optimal steady-state viscosity in the lower crust is similar to 5 x $\times $ 10(18) Pa s. We simulate the deformation due to the poroelastic rebound in the top 10 km upper crust. Model results indicate that the poroelastic rebound only produces a few millimeters surface deformation and may be a secondary-order postseismic process.