包体流变模型体应变场时空演变的理论分析

THEORETICAL ANALYSIS OF THE SPATIO-TEMPORAL EVOLUTION OF THE BULK-STRAIN FIELD BASED ON A RHEOLOGIC INCLUSION MODEL

基于包体流变模型的理论解 ,计算了三维粘弹性介质中球形硬包体与软包体在地面引起的体应变 .结果表明 ,球形硬包体的地面体应变随时间的变化曲线表现出特征不同的 3个阶段 (α,β,γ) .它与大量地形变资料出现的α,β,γ阶段相似 ;而球形软包体却没有此特征 .其中 ,α阶段的前兆在近源区和远源区都向外扩展 ;β阶段的前兆在近源区和远源区都处于极值状态 ;γ阶段前兆在远源区表现为向近源区收缩 ,而在近源区表现为向外扩展 .这些结果对地震前兆的时空演化过程阶段性的解释具有一定的启示 .

WT5BZ]Based on the theoretical expression of the three dimension rheologic inclusion model, we analyze in detail the spatio temporal evolution on the ground of the bulk strain produced by a spherical rheologic inclusion in a semi infinite rheologic medium. The results show that the spatio temporal evolution of the bulk strain produced by the hard inclusion has three stages of different characteristics, which are similar to most of those geodetic deformation curves, but that by a soft inclusion has not. The α stage is a long stage in which the precursors in both the near source region and the far field develop from the focal region to the periphery. The β stage indicates a very rapid propagation of the precursors, so that they almost appear everywhere. During the γ stage, the precursors in the far field converge from the periphery, and the precursors in the near source region develop outwards. The theoretical results have been used to explain tentatively the stage characteristics of the spatio temporal evolution of earthquake precursors.