On May 24th, Mr. Qin Tian defensed his master thesis “1976年唐山7.8级地震震后形变的三维黏弹性数值模拟”. In his thesis, Qin studied two main postseismic processes, that is, viscoelastic relaxation in the lower crust and upper mantle of the 1976 Tangshan earthquake. He constructed viscoelastic three-dimensional finite element models (FEM) of the earthquake based the coseismic rupture and rock physical properties. Based on the comparison of GPS observations with model predictions, he constrained the regional rheological structure of the viscoelastic lower crust and upper mantle. Model results indicate that viscosity of the viscoelastic lower crust and upper mantle is 1019 Pa s and 8×1019 Pa s, respectively. Aftershocks of the Tangshan earthquake still occur occasionally, which may be related to the high viscosity of the lower crust and thus longer time relaxation of earthquake-induced stresses.
Prepared by Siyuan Yang on Aug. 29th, 2023.
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