Research On Stress And Strain Field Of Eastern Tibet Margin Based On GPS Observations

Among all kind of natural disasters, earthquake which occurs suddenly and unpredictable has the greatest impact on human life. After long-term researches, seismologists generally believe that earthquake is a result of sudden rock rupture and split under the function of tectonic stress from the interior of earth that eventually causes varying degrees of deformations and damages. With the development of space measurement technology, the accurate transformation of crustal deformation and tectonic stress field based on GPS technology、geology and geophysics data can be used to explore the conceiving、occurring and developing rules of strong earthquake, thereby mitigating earthquake disasters.The geological structure of the eastern Tibet margin is very complex with intense tectonic activity. The paper researches on the change features of block deformation field and tectonic stress field in this area from the angle of crustal deformation and block fracture based on multi-phase GPS observation data to explore it’s motion mode of active faults, meanwhile,by calculating the Sichuan-Yunnan block’s tectonic stress by the boundary element method and simulating the evolution of regional seismic characteristics with geological background,the paper aimed at finding out the inducing factor and driving force of Wenchuan Earthquake.The main work and result are summarized as follows:1.Using the overall rotation linear strain method and multi-surface function method separately to calculate the crustal deformation and regional stress field change features of the eastern Tibet margin, research the overall block motion tendency and interior strain rate field and analyze the relation of tectonic tress field characteristics、geological structure distribution and seismic activity, which shows a good agreement.2.The tectonic stress field of eastern Tibet margin primarily represented by north-south pressure stress and supplemented by east-west tension, which is mainly controlled by the northward compressing of the Indian plate and southward propelling of the Eurasia plate so far. The displacement field of this area generally shows a trend of decrease from the south to the north and the principal stress highly concentrated in Sichuan and Yunnan area. Strong earthquakes at the same period, mainly happen in the area where the stress highly concentrated, strain values large-scaled changed and deep great fault lies.3.With the boundary element method, the paper testifies the influence of medium parameter within the Earth’s crust to the result of regional tectonic stress field. It shows that if the force boundary condition is constant, changing the Poisson’s ratio will affects the result of displacement field and tectonic stress field; changing the elastic modulus only changes the result of displacement field without the result of tectonic stress field; increasing the elastic modulus decreases the displacement value and strain variable, stress value increase with it,vice versa.4.To explore the deep tectonic characteristics of Longmenshan fault zone and the inducing factor and driving force of Wenchuan Earthquake, the paper analyzes the crustal deformation and deep dynamic mechanism of Sichuan-Yunnan region by boundary element method. It indicates that the Tibet plate migrates towards east caused by collision and northward extrusion of the Indian plate and the Eurasia blocked by the Yangtze plate, which generates highly concentration of stress field and energy, that leads to earth’s crust fracture and interior rupture.