Numerical Simulation Of The Relationship Between Deformation And Gravity Variation During Crustal Isostasy

Crustal deformation and material migration are important topics in modern geophysics and geodesy research.Any crustal movement process includes two most basic forms.One is the density change of the crustal medium itself,and the other is the displacement change caused by the deformation of the crustal medium.Studies have shown that there is a strong coupling relationship between the two,and the earth's gravity field changes with time.Change is one of the best reflections of this coupled movement.By studying and analyzing the time-varying characteristics of the gravitational field,we can understand the changes in the density of the earth's internal matter and the deformation of the earth's crust.The development of modern space geodetic surveying and terrestrial geodetic surveying technologies such as GNSS and gravity satellites and the continuous improvement of observation accuracy have provided geoscientists with more and more high-precision,high-resolution crustal deformation and gravity spatiotemporal changes..In actual gravity measurement,it is found that gravity will be affected by crustal deformation and movement.The gravity measurement in mountain area found that the gravity anomaly effect in this area is smaller than the theoretical calculation result.It is believed that there is a certain gravity balance compensation in mountain area,and it can be used.Airy and Pratt equilibrium models are explained.Airy and Pratt equilibrium models are suitable for explaining the relationship between static or long-period crustal deformation and gravity changes.However,in the short-term gravity change and short-term crustal deformation,there are more complicated factors such as stress and strain.Whether there is a more obvious equilibrium effect,and whether this equilibrium effect can reflect the basic characteristics of the relationship between crustal deformation and gravity is still not clear.Clearly,further research and discussion are needed.That is to say,the well-known gravity equilibrium theory is generally applicable to long-period,large-scale crustal deformation,but whether it is also applicable to short-term,small-scale crustal deformation is a question worthy of further study.Based on the coupled movement theory of deformation and density change,this paper derives the gravity change formulas in space and fixed points on the surface,and explores the ratio between the time change of gravity caused by the deformation movement and the crustal deformation.A simplified three-dimensional crustal movement model is established using the numerical integration discrete method to simulate the numerical relationship between gravity changes and surface deformation under crustal equilibrium.This is important for the promotion of static crustal equilibrium effects in time-varying situations and the characteristics of gravity changes caused by crustal movement.Discrimination and so on have certain reference value.Exploring the relationship between gravity change and surface deformation under the equilibrium condition of the crust is helpful to understand the cause of gravity change and the characteristics of crustal movement,and provides important theoretical guiding significance and reference value for the practical research of the theory.The main research work and results of this paper are summarized as follows:1)?The article mainly introduces the main content of the theory of coupled movement of crustal deformation and density change,and analyzes the calculation formula of gravity change at a fixed point in space and accompanying surface movement.Introduced the Airy or Pratt crustal equilibrium theory suitable for static conditions.The study believes that the existence of this equilibrium compensation effect conforms to the coupling relationship between crustal deformation and density,and can be used as a special case of the coupled movement of crustal deformation and density changes.Extend the application to the study of the dynamic process of the earth's crust and the timevarying gravity field.2)?Based on the basic theory of coupling movement of deformation and density change,combined with time-varying Airy model,several simple crustal movement models are designed to simulate several simple processes of double-layer crust model(crust-upper mantle)movement model,including bulge process,depression process and bulge to depression process,And the ratio relationship between gravity change and surface deformation.The results show that the gravity gradients are similar in different crustal movements,which are 3.6e,4.2e and 3.8e,respectively.The gravity vertical gradient value is close to the free air gradient(3.0E).3)?Based on the coupling theory of deformation and density change and following the dynamic Pratt model,several simple motion models of the uniform double-layer crustal model(crust-upper mantle)motion model are simulated,including the convex model,the depression model and the combination of the two The model simulates and calculates the gravity change during the crustal deformation process when the observation point is on the surface,and the ratio between gravity change and surface deformation.The results show that under the Pratt crustal equilibrium model,the gravity vertical gradients of different motion processes are approximately the same in value,which are-3.4E,-3.5E,and-3.6E,respectively.Comparing with Airy equilibrium,it is found that when the observation point is on the surface,the gravity changes produced by the Pratt equilibrium model are greater.As a result of the difference of the change in gravity with time,the gravity change produced by Pratt equilibrium is 50?gal larger than Airy equilibrium,and the gravity gradient is 0.9E larger.