Application of rock creep experiment in calculating the viscoelastic parameters of earth medium

摘要

Based on the rock creep experiment, the data of aftershock sequence and post-earthquake deformation are used to estimate the viscosity of crust medium near earthquake focus. Firstly 9 samples that belong to 3 kinds of rock are conducted in creep experiment under constant pressure to obtain the creep curves directly. Inversion results show that the standard linear model is the best one to present the earth medium. It exhibits obvious elasticity within a short time, while it exhibits obvious rheology within a long time. The relationship between element module μ_2 and the whole module μ of standard linear model or the module of real earth medium is calculated and analyzed. On the basis of μ_2 = 25 μ, the sequence of aftershock of Gonghe earthquake in Qinghai Province is analyzed and the relationship between accumulated released strain and the time is obtained, which, combined with the creep experiment results, is used to estimate the viscosity of crustal medium in this area. The measured vertical deformation after the same earthquake also is combined with the creep experiment results, then it is used to calculate the relaxation time and viscosity through three different methods respectively, i.e. inversion of Kelvin model, difference method of deformation and viscoelastic dislocation theory. The viscosity of crustal medium in 32 km depth of earthquake focus of Gonghe area deduced from the different data and methods is about 10~(19) Pa·s, which is the same as the research results by other authors at home and abroad.