The Research On Theory And Application Of Lithospheric Tectonic Stress Field Contributed By Gravitational Potential Energy Differences

Understanding of the distribution within the lithospheric stress field is important to constrain the forces that drive plate tectonics,to define compressional or tensional style of stress distribution and to explain the mechanism of lithospheric deformation.The horizontal variation of gravitational potential energy is one of the most significant sources of lithospheric stress field.Solving the force balance equation has proved to be an efficient way to determine the contribution of gravity to the lithospheric stress field.It's possible to seek a unique solution of temporal tectonic stress field induced by the gravitational potential energy variation which will be substituted into force balance equation.First,we propose a method to calculate horizontal tectonic stress contributed by gravitational potential energy,and analyze the difference between it and traditional method of computing deviatoric stress.Also,we provide a method to compute the temporal gravitational potential energy difference.Applying the theory to the Chuandian Area and North China Area,we analyze the role gravity plays in these areas.Finally,we discuss the tectonic stress change arising fromgravity change during the breeding process of some big earthquakes occurred in China mainland.Still,we discuss the relationship between stress regime and focal mechanism solutions.The main work of this thesis includes,? Method to calculate the horizontal force arising from gravitational potential energy differenceWe use horizontal tectonic stress containing the tectonics overpressure as the horizontal force induced by gravitational potential energy variation and establish the equilibrium equation between gravitational potential energy difference and horizontal tectonic stress.To eliminate one degree of freedom of equilibrium equation,the constraint which is minimizing the sum of the squared horizontal tectonic stress is proposed.Using constrained variational principle,the relationship between Lagrange multipliers and horizontal tectonic stresses is built subjected to constraint that balance equation are satisfied.We construct the functional for the finite element method and it is possible to derive the unique solution by minimizing the functional with respect to Lagrange multipliers.The method to calculate tectonic overpressure using the deviatoric stress and horizontal tectonic stress is discussed and we drive the formula to computer gravitational potential energy change through the GRACE temporal gravity data and ground gravity variational data.? Horizontal force contributed by gravitational potential energy difference in North China AreaWe compute the gravitational potential energy corrected by dynamical topography using Crust 1.0 model,EGM2008 gravity model and V18.1 topography model data set.The deviatoric stress and horizontal tectonic stress are calculated through the equilibrium equation with gravitational potential energy terms in a finite element method.The results show the same distribution style exist between the deviatoric stress and horizontal tectonic stress,but the magnitude of latter is a factor of two larger than the former.The comparison of the maximal horizontal principal orientations between horizontal forces induced by GPE and focal mechanism solution from WSM show that directions are different and even perpendicular to each other.We can infer that gravity is not the main source of tectonic stress field in North China Area.? Horizontal force induced by GPE difference in Chuandian AreaThe same data and methods are used to calculate GPE and horizontal force in Chuandian Area.The results indicate that the magnitude of deviatoric stress and horizontal tectonic stress are respectively range from 1002-11.105 MPa and 1.013-26.049 MPa,and the direction distribution is same.The maximal horizontal principal orientations between horizontal forces induced by GPE and focal mechanism solution from WSM agree well.This means gravity dominate the tectonic movement in Chuandian Area.? Horizontal force change arising from GPE variationWe calculate the GPE variations using the monthly GRACE solutions provided by CSR and horizontal forces change.There are accumulation of compressional stress because of terrestrial water storage decreasing.Taking Lijiang 7-magnitude earthquake as an example,we compute tectonic stress change as a result of pre-seismic gravity change.Computation reveals that accumulation of tensional stresses accompanying with gravity increasing before earthquake agree well with focal mechanism solution of normal fault type.