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强震后地表变形的动力学机制是地球动力学研究的重要方面,现在普遍认为震后变形主要由断层的震后余滑或由介质的黏弹性松弛所至.1999年台湾集集地震GPS观测系统记录到了空前的资料,为研究震后变形的动力学机制提供了难得的机会.本研究认为集集地震后地表变形由震后断层余滑、下地壳/上地幔的黏弹性松弛、震源区介质的破裂、孔隙弹性回跳、地下流体的运移、介质孔隙度及孔隙压的变化等多种因素共同影响决定.为抓住重点,研究中将介质的破裂、地下流体的运移和孔隙弹性回跳等因素等效为震源区介质的物性变化.文中运用黏弹性有限单元模型(麦克斯威尔体)、利用GPS观测的时间序列资料对震后余滑、地壳/地幔黏度以及等效的震源区介质物性变化进行了反演.反演模型给出了震后余滑的分布及变化特征,反演结果初步显示台湾地区的下地壳/上地幔的黏度分别为2.7×1018,4.2×1020Pa·s.此外,反演结果还给出每种影响因素对地表变形的贡献大小,在集集地震后的450d时间里,断层的震后余滑引起的地表变形占总变形的44.6%,下地壳/上地幔的黏性松弛占34.7%,等效的震源区介质的物性变化占20.7%.
The dynamic mechanism of surface deformation after strong earthquakes is an important aspect of geodynamic research. It is generally accepted that the post-earthquake deformation is mainly caused by the post-earthquake slip of the fault or by the viscoelastic relaxation of the medium. The system records unprecedented information and provides a rare opportunity to study the dynamic mechanism of the deformation after the earthquake.The study shows that the surface deformation after the Jiadian earthquake is caused by the post-earthquake faulting, the viscoelastic relaxation of the lower crust / upper mantle, Medium rupture, elastic rebound of pore, migration of underground fluid, change of porosity and pore pressure of media, etc. In order to seize the key points, we will study the medium rupture, migration of underground fluid and pore Elastic bounce and other factors are equivalent to the change of physical properties in the source region.Using the viscoelastic finite element model (Maxwell body), the time series data of GPS observations are used to study the post-earthquake slip, crust / mantle viscosity and equivalent The inversion of physical properties in the source region of the seismic source area is carried out.The inversion model gives the distribution and variation characteristics of the residual slip after the earthquake.The results of the inversion show that the lower crust / Respectively, and their viscosities are 2.7 × 1018 and 4.2 × 1020Pa · s, respectively. In addition, the inversion results also give the contribution of each factor to the deformation of the ground surface. After 450d after the earthquake, the post-earthquake slip caused by the fault The surface deformation accounts for 44.6% of the total deformation, and the viscous relaxation in the lower crust / upper mantle accounts for 34.7%. The equivalent source area changes 20.7% in physical properties.