关键词 ： 2011年日本MW9.0地震,  球体位错理论,  地幔黏滞性松弛,  断层余滑,  震后位移 

Abstract：This study optimized the thickness of the lithosphere and the viscosity of the mantle around the source of the 2011 Tohoku-Oki MW9.0 earthquake and reconstructed the process of the after-slips by using a relatively perfect spherical dislocation theory and the post-seismic displacements within 4.5 years after the main shock. Firstly, we extracted the post-seismic displacements caused by the 2011 Tohoku-Oki MW9.0 earthquake from 215 GPS continuous observation stations that are distributed evenly on Japan islands. The data span from 12 March 2009 to 12 September 2015. Next, using the viscoelastic dislocation theory we simulated the post-seismic displacements between 3 and 4.5 years after the main shock, which were caused completely by the viscoelastic relaxation of the mantle. Comparing the observed displacement with the simulated ones, we found that the optimal viscosity of the mantle and the thickness of the lithosphere are about 6×1018 Pa·s and 30 km, respectively.Then, we simulated the viscoelastic relaxation induced by the 2011 Tohoku-Oki MW9.0 earthquake within 3 years after the main shock and separated the displacements caused by after-slips from the observations of GPS. Finally, we obtained the distributions of after-slips in 12 periods, by using the inversion algorithm based on spherical dislocation theory. We found that after-slips following this earthquake changed significantly in 0.5 years and decayed completely in the area of the main shock after 2 years. However, the after-slips still existed in northeast and southwest of the fault model. The cumulative moment of after-slips in 2 years reached up to 8.59. The total displacements caused by the viscoelastic relaxation of the mantle would exceed that caused by after-slips in approximately 4 years after the great earthquake.