Study On The Relationship Between Surface Gravity Variation And Vertical Crustal Deformation

The earth’s gravity field is one of the most basic physical fields of the earth.It is a comprehensive reflection of the material distribution in the interior,surface and external space of the earth and the rotational motion information of the earth itself.Due to the uneven distribution of mass in the earth’s interior,coupled with the movement of the earth between celestial bodies and its own deformation,the earth’s gravity field will change with space and time.Among them,the temporal variation of the earth’s gravity field mainly includes the earth’s deformation,the movement of the earth’s internal mass,and the changes of some dynamic elements in the earth’s space movement.It is closely related to the research of modern geological tectonic movement,earthquake analysis and prediction and surface environment monitoring.Geodetic means(GNSS,InSAR,etc.)observe the geometric deformation information of the earth’s surface.It is a comprehensive reflection of the overall and local crustal movement information,and provides important boundary conditions for the study of crustal material movement.The change of the earth’s gravity field contains the information of density change and deformation(especially the crustal vertical deformation).It is necessary to combine the two.At the same time,the relationship between gravity change and crustal vertical deformation has rich geophysical meaning,which is of great significance to the study of the process of crustal material migration.Due to the limitations of early observation conditions and accuracy,as well as the lack of in-situ observation data of surface gravity and crustal vertical deformation,gravity and deformation are studied from their own perspectives,so it is difficult to capture the dynamic information of the earth’s interior.With the rapid development of modern precision geodesy technology and the largescale development of in-situ observation of surface gravity and deformation,the existing rich data are enough to provide the possibility to accurately analyze and study the relationship between gravity change and crustal vertical deformation on a large scale.With the continuous improvement of people’s understanding of the earth’s interior,the urgent need for the interpretation of geophysical phenomena and the rapid development of geodetic observation technology,it is imperative to conduct in-depth research combined with surface gravity and deformation data.Vigorously carrying out the theoretical and applied research of the two is of great significance to explore and understand the core problems in the field of Geoscience,such as the movement of matter in the earth’s interior and its dynamic process.Based on this,taking the eastern Tibetan Plateau and its surrounding areas,Changning earthquake area in Sichuan and Gravitation and Earth Tide National Observation and Research Station Wuhan(hereinafter referred to as "Wuhan station")as examples,this paper studies the characteristics of surface gravity change and crustal vertical deformation under different dynamic processes from three aspects of tectonic movement,seismic activity and environmental factors,and analyzes and discusses the relationship between gravity change and crustal vertical deformation.This paper consists of seven chapters:the first chapter is the introduction,which summarizes the research background,significance and research status of this paper;The second chapter mainly introduces the basic theory and analysis method of gravity change;The third chapter mainly introduces the processing method of gravity change observation data;In fourth chapter,taking the eastern Tibetan Plateau and its surrounding areas as an example,the relationship between gravity change and crustal vertical deformation in tectonic movement is analyzed;The fifth chapter takes the Changning earthquake in Sichuan Province as an example to analyze the relationship between gravity change and crustal vertical deformation in seismic activity.In sixth chapter,taking Wuhan station as an example,the relationship between gravity change and crustal vertical deformation in environmental factors is analyzed;The seventh chapter summarizes the main research work of this paper and looks forward to the next research work.The contribution and innovation of this paper mainly focus on the following four aspects:1.The ratio relationship between gravity change and crustal vertical deformation is discussed theoretically.When the ratio between them is in different ranges,or the ratio relationship between them is inconsistent or opposite in theory,the difference between this theory and actual data can reflect the different underground material migration processes in the process of crustal deformation,which lays a foundation for the study of the relationship between gravity change and crustal vertical deformation.2.Using gravity and GNSS data,the characteristics of gravity change,crustal vertical deformation and their relationship in the eastern Tibetan Plateau and its surrounding areas are studied.The results show that the gravity change characteristics of the eastern Tibetan Plateau are mainly dominated by the material migration of the underground plateau.The ratio of gravity change to crustal vertical deformation reflects the strength of material migration in different regions,which can provide an important reference for the study of the dynamic process of the Tibetan Plateau.3.Using gravity and GNSS data,the characteristics of gravity change,crustal vertical deformation and their relationship in Changning and its adjacent areas,Sichuan Province are studied.The results show that the long-term driving force of Changning earthquake area comes from the migration of materials from the Tibetan Plateau to the southern boundary of Sichuan Basin.In the epicenter and surrounding areas of the earthquake,there may be some cavities or air bags in the shallow layer of the surface,and the loss and filling of gas,liquid or high-density materials appear before and after the earthquake.The migration of surface materials triggers the change of local stress,especially related to salt production,gas production and wastewater reinjection in this area,which may be one of the reasons for the occurrence of Changning earthquake in Sichuan.4.Using gravity and GNSS data,the characteristics of gravity change,crustal vertical deformation and their relationship at Wuhan station are studied.The results show that the gravity change of Wuhan station is mainly affected by groundwater activities,and its existing law can be obtained from the point distribution map of the ratio of the two.