[S-GD02] 地殻変動

[SGD02-04] Rheological Heterogeneities in the Lower Crust in Southern and Western Tibet

*Yan Hu^1,2,3、Jian Zhang²、Yunguo Chen⁴、Bin Zhao⁵ (1.Institute of Deep Space Sciences, Deep Space Exploration Laboratory, Hefei 230088, China、2.School of Earth and Space Sciences, University of Science and Technology of China, Hefei 230026, China、3.CAS Center for Excellent in Comparative Planetology, University of Science and Technology of China, Hefei 230026, China、4.School of Transportation Engineering, East China Jiaotong University, Nanchang 330013, China、5.Institute of Seismology, China Earthquake Administration, Wuhan 430071, China)

キーワード：Postseismic deformation, Finite element model, Tibet plateau, Lithospheric rheology

Postseismic deformation of large earthquakes help constrain the rheological properties of the lithosphere and upper mantle. We have developed three dimensional viscoelastic finite element models to study deformation processes of the 2015 Mw7.8 Gorkha and 1997 Mw7.6 Manyi earthquakes. The model includes an elastic upper crust, viscoelastic lower crust and upper mantle. Viscoelastic relaxation of earthquake-induced stresses in the lower crust and upper mantle is simulated by the biviscous Burgers rheology. The time-dependent, stress-driven afterslip is simulated through a 2-km weak shear zone attached to the fault. The model successfully reproduces the overall pattern of GPS and InSAR observations. Model results indicate that the viscosity in the lower crust increases from about 3 x 10¹⁸ Pa s at the Tibet deformation front to about 5 x 10¹⁸ Pa s in the farther inland region. The afterslip of the fault takes place mostly within the first year after the earthquake and decays rapidly with time.