Mozambique's continental margin in East Africa was formed during the break-off stage of the east and west Gondwana lands. Studying the geological structure and division of continent-ocean boundary(COB) in Mozambiq...Mozambique's continental margin in East Africa was formed during the break-off stage of the east and west Gondwana lands. Studying the geological structure and division of continent-ocean boundary(COB) in Mozambique's continental margin is considered of great significance to rebuild Gondwana land and understand its movement mode. Along these lines, in this work, the initial Moho was fit using the known Moho depth from reflection seismic profiles, and a 3D multi-point constrained gravity inversion was carried out. Thus, highaccuracy Moho depth and crustal thickness in the study area were acquired. According to the crustal structure distribution based on the inversion results, the continental crust at the narrowest position of the Mozambique Channel was detected. According to the analysis of the crustal thickness, the Mozambique ridge is generally oceanic crust and the COB of the whole Mozambique continental margin is divided.展开更多
Three-dimensional gravity inversion based on the mass property model is very popular in recent years. The time and efficiency of inversion algorithms is relative to the magnitude of the target mesh. One approach is to...Three-dimensional gravity inversion based on the mass property model is very popular in recent years. The time and efficiency of inversion algorithms is relative to the magnitude of the target mesh. One approach is to search over the entire solution space for a more refined result. However, the inversion will be difficult with the increased parameters in the large search space and the number of computations increases exponentially. ｜n this paper, we propose a novel approach based on the frequency characteristics of the density distribution over the mesh. The purposes of our study are to reduce the parameters of three- dimensional gravity inversion and to lighten the image quality of the inversion result. The results show that the new method can expedite the inversion processing and get a better geological interpretation than tradition methods.展开更多
The gravity inversion is to restore genetic density distribution of the underground target to be explored for explaining the internal structure and distribution of the Earth.In this paper,we propose a new 3D gravity i...The gravity inversion is to restore genetic density distribution of the underground target to be explored for explaining the internal structure and distribution of the Earth.In this paper,we propose a new 3D gravity inversion method based on 3D U-Net++.Compared with two-dimensional gravity inversion,three-dimensional(3D)gravity inversion can more precisely describe the density distribution of underground space.However,conventional 3D gravity inversion method input is two-dimensional,the input and output of the network proposed in our method are three-dimensional.In the training stage,we design a large number of diversifi ed simulation model-data pairs by using the random walk method to improve the generalization ability of the network.In the test phase,we verify the network performance by using the model-data pairs generated by the simulation.To further illustrate the eff ectiveness of the algorithm,we apply the method to the inversion of the San Nicolas mining area,and the inversion results are basically consistent with the borehole measurement results.Moreover,the results of the 3D U-Net++inversion and the 3D U-Net inversion are compared.The density models of the 3D U-Net++inversion have higher resolution,more concentrated inversion results,and a clearer boundary of the density model.展开更多
Gravity inversion requires much computation,and inversion results are often non-unique.The first problem is often due to the large number of grid cells.Edge detection method,i.e.,tilt angle method of analytical signal...Gravity inversion requires much computation,and inversion results are often non-unique.The first problem is often due to the large number of grid cells.Edge detection method,i.e.,tilt angle method of analytical signal amplitude(TAS),helps to identify the boundaries of underground geological anomalies at different depths,which can be used to optimize the grid and reduce the number of grid cells.The requirement of smooth inversion is that the boundaries of the meshing area should be continuous rather than jagged.In this paper,the optimized meshing strategy is improved,and the optimized meshing region obtained by the TAS is changed to a regular region to facilitate the smooth inversion.For the second problem,certain constraints can be used to improve the accuracy of inversion.The results of analytic signal amplitude(ASA)are used to delineate the central distribution of geological bodies.We propose a new method using the results of ASA to perform local constraints to reduce the non-uniqueness of inversion.The guided fuzzy c-means(FCM)clustering algorithm combined with priori petrophysical information is also used to reduce the non-uniqueness of gravity inversion.The Open Acc technology is carried out to speed up the computation for parallelizing the serial program on GPU.In general,the TAS is used to reduce the number of grid cells.The local weighting and priori petrophysical constraint are used in conjunction with the FCM algorithm during the inversion,which improves the accuracy of inversion.The inversion is accelerated by the Open Acc technology on GPU.The proposed method is validated using synthetic data,and the results show that the efficiency and accuracy of gravity inversion are greatly improved by using the proposed method.展开更多
Focusing inversion is accomplished by the iterative of abnormal source to make the image gradually focused. It can better reflect the underground geological geometry and physical parameters. The model experiments in t...Focusing inversion is accomplished by the iterative of abnormal source to make the image gradually focused. It can better reflect the underground geological geometry and physical parameters. The model experiments in the study show that gravity focusing inversion allows inversion image stabilization and polymerization,which solves the multiple solutions and instability of inversion and so on. The method is applied to measured gravity data processing of certain region of Changbai Mountain,compared to Euler deconvolution,the results show that the method for determining the horizontal position and depth of underground anomalies has good efforts.展开更多
We present a 3D inversion method to recover density distribution from gravity data in space domain.Our method firstly employs 3D correlation image of the vertical gradient of gravity data as a starting model to genera...We present a 3D inversion method to recover density distribution from gravity data in space domain.Our method firstly employs 3D correlation image of the vertical gradient of gravity data as a starting model to generate a higher resolution image for inversion.The 3D density distribution is then obtained by inverting the correlation image of gravity data to fit the observed data based on classical inversion method of the steepest descent method.We also perform the effective equivalent storage and subdomain techniques in the starting model calculation,the forward modeling and the inversion procedures,which allow fast computation in space domain with reducing memory consumption but maintaining accuracy.The efficiency and stability of our method is demonstrated on two sets of synthetic data and one set of the Northern Sinai Peninsula gravity data.The inverted 3D density distributions show that high density bodies beneath Risan Aniza and low density bodies exist to the southeast of Risan Aniza at depths between 1~10 and 20 km,which may be originated from hot anomalies in the lower crust.The results show that our inversion method is useful for 3D quantitative interpretation.展开更多
A 3D crustal model was constructed using a combination of cutting-edge techniques,which were integrated to provide a density model for Egypt and address the sporadic distribution of seismic data.These techniques inclu...A 3D crustal model was constructed using a combination of cutting-edge techniques,which were integrated to provide a density model for Egypt and address the sporadic distribution of seismic data.These techniques include obtaining gravity data from the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE),creating seismic profiles,analyzing the receiver functions of seismic data,obtaining information from boreholes,and providing geological interpretations.GOCE satellite gravity data were processed to construct a preliminary model based on nonlinear inversions of the data.A regional crustal thickness model was developed using receiver functions,seismic refraction profiles,and geological insights.The inverted model was validated using borehole data and compared with seismic estimates.The model exhibited strong consistency and revealed a correlation between crustal thickness,geology,and tectonics of Egypt.It showed that the shallowest depths of the Moho are located in the north along the Mediterranean Sea and in the eastern part along the Red Sea,reflecting an oceanic plate with a thin,high-density crust.The deepest Moho depths are located in the southwestern part of Egypt,Red Sea coastal mountains,and Sinai Peninsula.The obtained 3D model of crustal thickness provided finely detailed Moho depth estimates that aligned closely with geology and tectonic characteristics of Egypt,contributing valuable insights into the subsurface structure and tectonic processes of region.展开更多
On September 5, 2022, an earthquake of magnitude M_(S)6.8 occurred in Luding County, Sichuan Province.This earthquake occurred at the key part of the southeast-clockwise extrusion of material on the eastern margin of ...On September 5, 2022, an earthquake of magnitude M_(S)6.8 occurred in Luding County, Sichuan Province.This earthquake occurred at the key part of the southeast-clockwise extrusion of material on the eastern margin of the Qinghai Plateau, the Y-shaped confluence of the Xianshuihe, Longmenshan and Anninghe fault zones. In this study, the three-dimensional dynamic crustal density changes in the earthquake area are obtained by the typical gravity change data from 2019 to 2022 before the earthquake and gravity inversion by growing bodies. The results indicate that gravity changes presented an obvious fourquadrant and gradient belt distribution in the Luding area before the earthquake. The threedimensional density horizontal slices show that small density changes occurred at the epicenter in the mid-to-upper crust between 2019.9-2020.9 and 2019.9-2021.9. At the same time, the surrounding areas exhibited a positive and negative quadrant distribution. These observations indicate that the source region was likely in a stable locked state, with locking-in shear forces oriented in the NW and NE directions. From 2021.9 to 2022.8, the epicentral region showed negative density changes, indicating that the source region was in the expansion stage, approaching a near-seismic state. The three-dimensional density vertical slices reveal a southeastward migration of positive and negative densities near the epicenter and on the western of the Xianshuihe Fault Zone, indicating that the material is flowing out to the southeast. The observed local negative density changes at the epicenter along the Longmenshan Fault Zone are likely associated with the NE-oriented extensional stress shown by the seismic source mechanism. The above results can provide a basis for interpreting pre-earthquake gravity and density changes,thereby contributing to the advancement of earthquake precursor theory.展开更多
Based on the synchronous joint gravity and magnetic inversion of single interface by Pilkington and the need of revealing Cenozoic and crystalline basement thickness in the new round of oil-gas exploration, we propose...Based on the synchronous joint gravity and magnetic inversion of single interface by Pilkington and the need of revealing Cenozoic and crystalline basement thickness in the new round of oil-gas exploration, we propose a joint gravity and magnetic inversion methodfor two-layer models by concentrating on the relationship between the change of thicknessI and position of the middle layer and anomaly and discuss the effects of the key parameters. Model tests and application to field data show the validity of this method.展开更多
Tikhonov regularization（TR） method has played a very important role in the gravity data and magnetic data process. In this paper, the Tikhonov regularization method with respect to the inversion of gravity data is d...Tikhonov regularization（TR） method has played a very important role in the gravity data and magnetic data process. In this paper, the Tikhonov regularization method with respect to the inversion of gravity data is discussed. and the extrapolated TR method（EXTR） is introduced to improve the fitting error. Furthermore, the effect of the parameters in the EXTR method on the fitting error, number of iterations, and inversion results are discussed in details. The computation results using a synthetic model with the same and different densities indicated that. compared with the TR method, the EXTR method not only achieves the a priori fitting error level set by the interpreter but also increases the fitting precision, although it increases the computation time and number of iterations. And the EXTR inversion results are more compact than the TR inversion results, which are more divergent. The range of the inversion data is closer to the default range of the model parameters, and the model features and default model density distribution agree well.展开更多
The 4.20 Lushan Ms7.0 earthquake occurred on the southwest segment of the Longmenshan fault on 20 April 2013. Some meaningful information on the prepa- ration and occurrence of this earthquake was found based on the d...The 4.20 Lushan Ms7.0 earthquake occurred on the southwest segment of the Longmenshan fault on 20 April 2013. Some meaningful information on the prepa- ration and occurrence of this earthquake was found based on the dynamic variation of gravity （DVG）. To examine the great progress of the Lushan earthquake, we obtained the density variation （DENV） derived from the DVG using the compact gravity inversion method in this article. The inversion results reveal three main findings： （1） the DENV in the crust in the Jinshajiang fault area changed from positive in 2010-2011 to negative in 2011-2012. （2） The DENV in the Xianshuihe fault area decreased continuously from 2010 to 2012. （3） The DENV of the uppermost mantle of South China decreased in 2010-2011 and increased in 2011-2012. We propose that the flow/expansion of the middle-lower crust beneath the Bayan Har block and Moho subsidence on the southwest margin of the Chuan-Dian block may have been the major causes of the Lushan earthquake.展开更多
The stretched structure and heterogeneity of the crust of the Nansha Block,the southern continental margin of the South China Sea(SCS),are not well understood.We used published ocean bottom seismic(OBS)/multichannel r...The stretched structure and heterogeneity of the crust of the Nansha Block,the southern continental margin of the South China Sea(SCS),are not well understood.We used published ocean bottom seismic(OBS)/multichannel reflection seismic(MCS)profiles across the Nansha Block to establish five two-dimensional crustal structure models.Using gravity modelling with magnetic anomaly inversion,we obtained the distribution of density and local magnetic susceptibility of the crust.The models show that the distribution of density and thickness of the upper crust in the Nansha Block is uneven,and the thick upper crust is prevalent in the regions close to the continent-ocean transition(COT)showing different characteristics.The interpreted Mesozoic granite blocks and Precambrian rigid basement reflects the heterogeneity in the material composition of the SCS continental margin.Based on the thinning styles of different crustal layers,we suggest that the Nansha Block has a three-layer thinning pattern.The uppermost pre-rift layer was deformed via brittle fractures,the upper crust was sheared by discrete shear zones,and the lower crust experienced ductile deformation.The inherited pre-rift thermal regime,mechanical state,and material composition of the SCS continental margin affected the extensional structure of the crust.展开更多
In order to improve the processing and interpretation of gravity data, multiscale edge theory in image processing is introduced into the study of gravity field. Multiscale edges of gravity anomaly are analyzed based o...In order to improve the processing and interpretation of gravity data, multiscale edge theory in image processing is introduced into the study of gravity field. Multiscale edges of gravity anomaly are analyzed based on a special wavelet. It shows that the multiscale edges are the extrema points of the horizontal gravity gradient at different heights, which are related to the sharp discontinuities of underground sources. The applications of multiscale edge in downward continuation and gravity inversion are discussed. The simulated examples show that the multiscale edges can be applied to stabilize the downward continuation operator when the continuation height is low. The multiscale edges also have a convenient application to infer the geometry of the underground source. Moreover, the gravity inversion algorithm based on the multiscale edges has a good antinoise property.展开更多
Based on a satellite constellation composed of two GRACE-type satellite formations with different inclinations(near polar orbit + low inclination) and the theory of repeat orbit cycle, we discuss the methods for selec...Based on a satellite constellation composed of two GRACE-type satellite formations with different inclinations(near polar orbit + low inclination) and the theory of repeat orbit cycle, we discuss the methods for selecting medium-low inclinations for global and local gravity fields. The effects of this constellation configuration on gravity field inversion are comparatively analyzed using a whole-course dynamics simulation. The results show that compared with the single GRACE-type satellite formation,the use of satellite constellations with different inclination configurations improves the gravity solution precision by 34%. The inclusion of multi-directional observations can improve the spatio-temporal resolution of the satellite missions, and yield gravity field solutions with higher isotropic sensitivity.Furthermore, it is necessary to select the optimal low inclination according to the study area, which will have a significant influence on the gravity field solution.展开更多
Based on the absolute and relative gravity observations in North China from 2009 to 2014,spatial dynamic variations of the regional gravity field are obtained. We employed the Euler deconvolution method and the theore...Based on the absolute and relative gravity observations in North China from 2009 to 2014,spatial dynamic variations of the regional gravity field are obtained. We employed the Euler deconvolution method and the theoretical model to get the best estimates of parameters. Gravity field change caused by the depth and distribution in North China is calculated by back analysis. The results show the structural index that equals 1 is suitable for inversion of the gravity variation data. The inversion results indicate that the depths of anomaly field sources are spread over the Hetao fault. The research method of this paper can be used in the quantitative study on the field source and may shed new light on the interpretations of gravity change, and also provide quantitative basis for earthquake prediction index criterions based on the gravity change.展开更多
Cosmological expansion or inflation is mathematically described by the theoretical notion of inverse gravity whose variations are parameterized by a factor that is a function of the distance to which cosmological expa...Cosmological expansion or inflation is mathematically described by the theoretical notion of inverse gravity whose variations are parameterized by a factor that is a function of the distance to which cosmological expansion takes prominence over gravity. This assertion is referred to as the inverse gravity inflationary assertion. Thus, a correction to Newtonian gravitational force is introduced where a parameterized inverse gravity force term is incorporated into the classical Newtonian gravitational force equation where the inverse force term is negligible for distances less than the distance to which cosmological expansion takes prominence over gravity. Conversely, at distances greater than the distance to which cosmological expansion takes prominence over gravity. The inverse gravity term is shown to be dominant generating universal inflation. Gravitational potential energy is thence defined by the integral of the difference (or subtraction) between the conventional Newtonian gravitational force term and the inverse gravity term with respect to radius (r) which allows the formulation, incorporation, and mathematical description to and of gravitational redshift, the Walker-Robertson scale factor, the Robinson-Walker metric, the Klein-Gordon lagrangian, and dark energy and its relationship to the energy of the big bang in terms of the Inverse gravity inflationary assertion. Moreover, the dynamic pressure of the expansion of a cosmological fluid in a homogeneous isotropic universe is mathematically described in terms of the inverse gravity inflationary assertion using the stress-energy tensor for a perfect fluid. Lastly, Einstein’s field equations for the description of an isotropic and homogeneous universe are derived incorporating the mathematics of the inverse gravity inflationary assertion to fully show that the theoretical concept is potentially interwoven into the cosmological structure of the universe.展开更多
The Guxiang-Tongmai segment of the Jiali fault is situated northeast of the Namche Barwa Syntaxis in northeastern Xizang.It is one of the most active strike-slip faults near the syntaxis and plays a pivotal role in th...The Guxiang-Tongmai segment of the Jiali fault is situated northeast of the Namche Barwa Syntaxis in northeastern Xizang.It is one of the most active strike-slip faults near the syntaxis and plays a pivotal role in the examination of seismic activity within the eastern Himalayan Syntaxis.New study in the research region has yielded a 1:200000 gravity dataset covering an area 1500 km^(2).Using wavelet transform multiscale decomposition,scratch analysis techniques,and 3D gravity inversion methods,gravity anomalies,fault distributions,and density structures were determined across various scales.Through the integration of our new gravity data with other geophysical and geological information,our findings demonstrate substantial variations in the overall crustal density within the region,with the fault distribution closely linked to these density fluctuations.Disparities in stratigraphic density are important causes of variations in the capacity of geological formations to endure regional tectonic stress.Earthquakes are predominantly concentrated within the density transition zone and are primarily situated in regions of elevated density.The hanging wall stress within the Guxiang-Tongmai segment of the Jiali fault exhibits a notable concentration,marked by pronounced anisotropy,and is positioned within the density differential zone,which is prone to earthquakes.展开更多
The South China continental margin spans various land-sea tectonic units,including the Jiangnan orogenic belt,the Cathaysia Block,and the northern margin of the South China Sea,exhibiting significant crustal structura...The South China continental margin spans various land-sea tectonic units,including the Jiangnan orogenic belt,the Cathaysia Block,and the northern margin of the South China Sea,exhibiting significant crustal structural differences.The widespread exposure of Mesozoic granites in South China reveals extensive tectonic-magmatic activities in the region.Therefore,in-depth research into the deep structure of the South China continental margin is of great significance for understanding the tectonic evolution and resource effects of the area.This paper focuses on the South China and northern South China Sea regions,employing the Hamiltonian Monte Carlo(HMC) three-dimensional density gravity inversion method,combined with deep seismic sounding and ocean bottom seismometer data,to establish a three-dimensional density model covering the land-sea extent of the South China continental margin.The density structure reveals Moho depths of 28-48 km in the South China continent,22-28 km in the northern margin of the South China Sea,and 10-20 km in the northwestern sub-basin,with the Moho surface rising from land to sea.Based on the density characteristics of granites in the region,the possible distribution ranges of granite bodies are delineated.The results show that the bottom boundaries of the Miaoershan-Yuechengling and Zhuguangshan-Wanyangshan granite bodies extend approximately 12-15 km,while the bottom boundaries of the Fogang and Darongshan-Shiwandashan granite bodies are at depths of about 4-5 km.The crustal structure of the South China continental margin thickens from sea to land,superimposed with local crustal thinning,reflecting the complex tectonic changes of the South China continent and the comprehensive influence of multi-phase tectonic-magmatic activities.The depth distribution of large granite bodies inferred from the density structure provides a basis for exploring deep tectonic-magmatic activities and their impact on mineralization in the region.展开更多
Gravity field is the most basic physical field generated by the material properties of the Earth system.It reflects the spatial distribution,movement and change of materials determined by the interaction and dynamic p...Gravity field is the most basic physical field generated by the material properties of the Earth system.It reflects the spatial distribution,movement and change of materials determined by the interaction and dynamic process inside the Earth.Over the years,a variety of technical means have been used to detect the Earth’s gravity field and supported numerous studies on the global change,resource detection,geological structure movement,water resources change and other related fields of research.Here is part of the progress in surface and marine gravimetry obtained by Chinese geodesy scientists from 2019 to 2023 from the following aspects,including:①Continuous gravity network in Chinese mainland;②Application of superconducting gravity measurement;③Network adjustment for continental-scale gravity survey campaign and data quality control;④Regional time-variable gravity field and its application;⑤Research progress on novel technologies for gravity inversion;⑥Research progress on marine gravity field determination;⑦Application research on marine gravity field.展开更多
The southern segment of the North-South Seismic Belt in China is a critical region for earthquake preparedness and risk reduction efforts.However,limited by the low density of seismic stations and the use of single-pa...The southern segment of the North-South Seismic Belt in China is a critical region for earthquake preparedness and risk reduction efforts.However,limited by the low density of seismic stations and the use of single-parameter physical structural models,the deep tectonic features and seismogenic environment in this area remain controversial.Thus,a comprehensive analysis based on high-resolution crustal structures and multiple physical parameters is required.In this study,we applied the ambient noise tomography method to obtain the three-dimensional(3D)crustal S-wave velocity structure using continuous waveform data from 112 permanent stations and 350 densely distributed temporary stations in the southern segment of the North-South Seismic Belt.Then,we obtained the high-resolution 3D density structure through wavenumber-domain 3D gravity imaging constrained by the velocity structure.The low-velocity and low-density anomalies in the upper crust of the study area were mainly distributed in the Sichuan Basin and around Dali and Simao,while the high-velocity and high-density anomalies were primarily distributed in the Panxi region,corresponding to the surface geological features.Two prominent low-velocity and low-density anomalies were observed in the middle and lower crust:one to the west of the Songpan-Garzêblock and Sichuan-Yunnan diamond-shaped block,and the other near the Anninghe-Xiaojiang fault.Combined with the spatial distribution of seismic events in the study area,we found that previous earthquakes predominantly occurred in the transition zones between high and low anomaly regions and in the low-velocity and low-density zones in the upper crust.In contrast,moderate-to-strong earthquakes mainly occurred within the transition zones between high and low anomaly regions and close to the high-velocity and high-density regions,often with low-velocity and low-density layers below their hypocenters.Fluids play a critical role in the seismogenic process by reducing fault strength and destabilizing the stress state,which may be a triggering factor for earthquakes in the study area.Additionally,the upwelling of molten materials from the mantle may lead to energy accumulation and stress conce-ntration,providing an important seismogenic background for moderate-to-strong earthquakes in this area.展开更多
基金The National Natural Science Foundation of China under contract No. 42076078China–Mozambique Joint Cruise under contract No. GASI-01-DLJHJ-CM。
文摘Mozambique's continental margin in East Africa was formed during the break-off stage of the east and west Gondwana lands. Studying the geological structure and division of continent-ocean boundary(COB) in Mozambique's continental margin is considered of great significance to rebuild Gondwana land and understand its movement mode. Along these lines, in this work, the initial Moho was fit using the known Moho depth from reflection seismic profiles, and a 3D multi-point constrained gravity inversion was carried out. Thus, highaccuracy Moho depth and crustal thickness in the study area were acquired. According to the crustal structure distribution based on the inversion results, the continental crust at the narrowest position of the Mozambique Channel was detected. According to the analysis of the crustal thickness, the Mozambique ridge is generally oceanic crust and the COB of the whole Mozambique continental margin is divided.
基金supported by the Key Project Fund of the Chinese Academy of Sciences under grant number (kzcx2-yw-203-01)the Major State Basic Research Development Program of China(973 Program,Grant No.2007CB41170404)
文摘Three-dimensional gravity inversion based on the mass property model is very popular in recent years. The time and efficiency of inversion algorithms is relative to the magnitude of the target mesh. One approach is to search over the entire solution space for a more refined result. However, the inversion will be difficult with the increased parameters in the large search space and the number of computations increases exponentially. ｜n this paper, we propose a novel approach based on the frequency characteristics of the density distribution over the mesh. The purposes of our study are to reduce the parameters of three- dimensional gravity inversion and to lighten the image quality of the inversion result. The results show that the new method can expedite the inversion processing and get a better geological interpretation than tradition methods.
基金supported by the Key Laboratory of Geological Survey and Evaluation of Ministry of Education (China University of Geosciences)(No. GLAB2020ZR13)
文摘The gravity inversion is to restore genetic density distribution of the underground target to be explored for explaining the internal structure and distribution of the Earth.In this paper,we propose a new 3D gravity inversion method based on 3D U-Net++.Compared with two-dimensional gravity inversion,three-dimensional(3D)gravity inversion can more precisely describe the density distribution of underground space.However,conventional 3D gravity inversion method input is two-dimensional,the input and output of the network proposed in our method are three-dimensional.In the training stage,we design a large number of diversifi ed simulation model-data pairs by using the random walk method to improve the generalization ability of the network.In the test phase,we verify the network performance by using the model-data pairs generated by the simulation.To further illustrate the eff ectiveness of the algorithm,we apply the method to the inversion of the San Nicolas mining area,and the inversion results are basically consistent with the borehole measurement results.Moreover,the results of the 3D U-Net++inversion and the 3D U-Net inversion are compared.The density models of the 3D U-Net++inversion have higher resolution,more concentrated inversion results,and a clearer boundary of the density model.
基金supported by the National Key Research and Development Program of China Project(Grant No.2018YFC0603502)
文摘Gravity inversion requires much computation,and inversion results are often non-unique.The first problem is often due to the large number of grid cells.Edge detection method,i.e.,tilt angle method of analytical signal amplitude(TAS),helps to identify the boundaries of underground geological anomalies at different depths,which can be used to optimize the grid and reduce the number of grid cells.The requirement of smooth inversion is that the boundaries of the meshing area should be continuous rather than jagged.In this paper,the optimized meshing strategy is improved,and the optimized meshing region obtained by the TAS is changed to a regular region to facilitate the smooth inversion.For the second problem,certain constraints can be used to improve the accuracy of inversion.The results of analytic signal amplitude(ASA)are used to delineate the central distribution of geological bodies.We propose a new method using the results of ASA to perform local constraints to reduce the non-uniqueness of inversion.The guided fuzzy c-means(FCM)clustering algorithm combined with priori petrophysical information is also used to reduce the non-uniqueness of gravity inversion.The Open Acc technology is carried out to speed up the computation for parallelizing the serial program on GPU.In general,the TAS is used to reduce the number of grid cells.The local weighting and priori petrophysical constraint are used in conjunction with the FCM algorithm during the inversion,which improves the accuracy of inversion.The inversion is accelerated by the Open Acc technology on GPU.The proposed method is validated using synthetic data,and the results show that the efficiency and accuracy of gravity inversion are greatly improved by using the proposed method.
文摘Focusing inversion is accomplished by the iterative of abnormal source to make the image gradually focused. It can better reflect the underground geological geometry and physical parameters. The model experiments in the study show that gravity focusing inversion allows inversion image stabilization and polymerization,which solves the multiple solutions and instability of inversion and so on. The method is applied to measured gravity data processing of certain region of Changbai Mountain,compared to Euler deconvolution,the results show that the method for determining the horizontal position and depth of underground anomalies has good efforts.
基金the Institute of Crustal Dynamics,China Earthquake Administration(Grant No.ZDJ2019-09)the National Science Foundation of China(Grant No.41704086)the National Key Research&Development Program(2016YFC060110401).
文摘We present a 3D inversion method to recover density distribution from gravity data in space domain.Our method firstly employs 3D correlation image of the vertical gradient of gravity data as a starting model to generate a higher resolution image for inversion.The 3D density distribution is then obtained by inverting the correlation image of gravity data to fit the observed data based on classical inversion method of the steepest descent method.We also perform the effective equivalent storage and subdomain techniques in the starting model calculation,the forward modeling and the inversion procedures,which allow fast computation in space domain with reducing memory consumption but maintaining accuracy.The efficiency and stability of our method is demonstrated on two sets of synthetic data and one set of the Northern Sinai Peninsula gravity data.The inverted 3D density distributions show that high density bodies beneath Risan Aniza and low density bodies exist to the southeast of Risan Aniza at depths between 1~10 and 20 km,which may be originated from hot anomalies in the lower crust.The results show that our inversion method is useful for 3D quantitative interpretation.
文摘A 3D crustal model was constructed using a combination of cutting-edge techniques,which were integrated to provide a density model for Egypt and address the sporadic distribution of seismic data.These techniques include obtaining gravity data from the Gravity Field and Steady-State Ocean Circulation Explorer(GOCE),creating seismic profiles,analyzing the receiver functions of seismic data,obtaining information from boreholes,and providing geological interpretations.GOCE satellite gravity data were processed to construct a preliminary model based on nonlinear inversions of the data.A regional crustal thickness model was developed using receiver functions,seismic refraction profiles,and geological insights.The inverted model was validated using borehole data and compared with seismic estimates.The model exhibited strong consistency and revealed a correlation between crustal thickness,geology,and tectonics of Egypt.It showed that the shallowest depths of the Moho are located in the north along the Mediterranean Sea and in the eastern part along the Red Sea,reflecting an oceanic plate with a thin,high-density crust.The deepest Moho depths are located in the southwestern part of Egypt,Red Sea coastal mountains,and Sinai Peninsula.The obtained 3D model of crustal thickness provided finely detailed Moho depth estimates that aligned closely with geology and tectonic characteristics of Egypt,contributing valuable insights into the subsurface structure and tectonic processes of region.
基金the National Natural Science Foundation of China(Grant No.42374105,42204089,42174104)Scientific Research Fund of Institute of Seismology,China Earthquake Administration(Grant No.IS202326341,IS202336350).
文摘On September 5, 2022, an earthquake of magnitude M_(S)6.8 occurred in Luding County, Sichuan Province.This earthquake occurred at the key part of the southeast-clockwise extrusion of material on the eastern margin of the Qinghai Plateau, the Y-shaped confluence of the Xianshuihe, Longmenshan and Anninghe fault zones. In this study, the three-dimensional dynamic crustal density changes in the earthquake area are obtained by the typical gravity change data from 2019 to 2022 before the earthquake and gravity inversion by growing bodies. The results indicate that gravity changes presented an obvious fourquadrant and gradient belt distribution in the Luding area before the earthquake. The threedimensional density horizontal slices show that small density changes occurred at the epicenter in the mid-to-upper crust between 2019.9-2020.9 and 2019.9-2021.9. At the same time, the surrounding areas exhibited a positive and negative quadrant distribution. These observations indicate that the source region was likely in a stable locked state, with locking-in shear forces oriented in the NW and NE directions. From 2021.9 to 2022.8, the epicentral region showed negative density changes, indicating that the source region was in the expansion stage, approaching a near-seismic state. The three-dimensional density vertical slices reveal a southeastward migration of positive and negative densities near the epicenter and on the western of the Xianshuihe Fault Zone, indicating that the material is flowing out to the southeast. The observed local negative density changes at the epicenter along the Longmenshan Fault Zone are likely associated with the NE-oriented extensional stress shown by the seismic source mechanism. The above results can provide a basis for interpreting pre-earthquake gravity and density changes,thereby contributing to the advancement of earthquake precursor theory.
基金Supported by the National Natural Science Foundation of China(Grant No.40674063)National Hi-tech Research and Development Program of China(863Program)(Grant No.2006AA09Z311)
文摘Based on the synchronous joint gravity and magnetic inversion of single interface by Pilkington and the need of revealing Cenozoic and crystalline basement thickness in the new round of oil-gas exploration, we propose a joint gravity and magnetic inversion methodfor two-layer models by concentrating on the relationship between the change of thicknessI and position of the middle layer and anomaly and discuss the effects of the key parameters. Model tests and application to field data show the validity of this method.
基金supported by the National Scientific and Technological Plan(Nos.2009BAB43B00 and 2009BAB43B01)
文摘Tikhonov regularization（TR） method has played a very important role in the gravity data and magnetic data process. In this paper, the Tikhonov regularization method with respect to the inversion of gravity data is discussed. and the extrapolated TR method（EXTR） is introduced to improve the fitting error. Furthermore, the effect of the parameters in the EXTR method on the fitting error, number of iterations, and inversion results are discussed in details. The computation results using a synthetic model with the same and different densities indicated that. compared with the TR method, the EXTR method not only achieves the a priori fitting error level set by the interpreter but also increases the fitting precision, although it increases the computation time and number of iterations. And the EXTR inversion results are more compact than the TR inversion results, which are more divergent. The range of the inversion data is closer to the default range of the model parameters, and the model features and default model density distribution agree well.
基金supported by the National Natural Science Foundation of China (41304060)the National Key Basic Research Program of China (973 Program, 2013CB733305)Scientific Investigation of April 20, 2013 M7.0 Lushan, Sichuan Earthquake
文摘The 4.20 Lushan Ms7.0 earthquake occurred on the southwest segment of the Longmenshan fault on 20 April 2013. Some meaningful information on the prepa- ration and occurrence of this earthquake was found based on the dynamic variation of gravity （DVG）. To examine the great progress of the Lushan earthquake, we obtained the density variation （DENV） derived from the DVG using the compact gravity inversion method in this article. The inversion results reveal three main findings： （1） the DENV in the crust in the Jinshajiang fault area changed from positive in 2010-2011 to negative in 2011-2012. （2） The DENV in the Xianshuihe fault area decreased continuously from 2010 to 2012. （3） The DENV of the uppermost mantle of South China decreased in 2010-2011 and increased in 2011-2012. We propose that the flow/expansion of the middle-lower crust beneath the Bayan Har block and Moho subsidence on the southwest margin of the Chuan-Dian block may have been the major causes of the Lushan earthquake.
基金Supported by the National Natural Science Foundation of China(Nos.42076078,41776057,42176055)the Open Foundation of Key Laboratory of Submarine Geosciences,Ministry of Natural Resources(No.KLSG2004)。
文摘The stretched structure and heterogeneity of the crust of the Nansha Block,the southern continental margin of the South China Sea(SCS),are not well understood.We used published ocean bottom seismic(OBS)/multichannel reflection seismic(MCS)profiles across the Nansha Block to establish five two-dimensional crustal structure models.Using gravity modelling with magnetic anomaly inversion,we obtained the distribution of density and local magnetic susceptibility of the crust.The models show that the distribution of density and thickness of the upper crust in the Nansha Block is uneven,and the thick upper crust is prevalent in the regions close to the continent-ocean transition(COT)showing different characteristics.The interpreted Mesozoic granite blocks and Precambrian rigid basement reflects the heterogeneity in the material composition of the SCS continental margin.Based on the thinning styles of different crustal layers,we suggest that the Nansha Block has a three-layer thinning pattern.The uppermost pre-rift layer was deformed via brittle fractures,the upper crust was sheared by discrete shear zones,and the lower crust experienced ductile deformation.The inherited pre-rift thermal regime,mechanical state,and material composition of the SCS continental margin affected the extensional structure of the crust.
基金Supported by the National Natural Science Foundation of China(No.40704003)the National 973 Program of China(No.2007CB714405)the Open Research Fund from Key Laboratory of Geospace Environment and Geodesy(No.04-01-08)
文摘In order to improve the processing and interpretation of gravity data, multiscale edge theory in image processing is introduced into the study of gravity field. Multiscale edges of gravity anomaly are analyzed based on a special wavelet. It shows that the multiscale edges are the extrema points of the horizontal gravity gradient at different heights, which are related to the sharp discontinuities of underground sources. The applications of multiscale edge in downward continuation and gravity inversion are discussed. The simulated examples show that the multiscale edges can be applied to stabilize the downward continuation operator when the continuation height is low. The multiscale edges also have a convenient application to infer the geometry of the underground source. Moreover, the gravity inversion algorithm based on the multiscale edges has a good antinoise property.
基金financially supported by the National Key R&D Program of China (2018YFC1503503)the National Natural Science Foundation of China (41974012)。
文摘Based on a satellite constellation composed of two GRACE-type satellite formations with different inclinations(near polar orbit + low inclination) and the theory of repeat orbit cycle, we discuss the methods for selecting medium-low inclinations for global and local gravity fields. The effects of this constellation configuration on gravity field inversion are comparatively analyzed using a whole-course dynamics simulation. The results show that compared with the single GRACE-type satellite formation,the use of satellite constellations with different inclination configurations improves the gravity solution precision by 34%. The inclusion of multi-directional observations can improve the spatio-temporal resolution of the satellite missions, and yield gravity field solutions with higher isotropic sensitivity.Furthermore, it is necessary to select the optimal low inclination according to the study area, which will have a significant influence on the gravity field solution.
基金funded by the Natural Science Foundation of China(61627824,41274083)the Youth Foundation of Earthquake Prediction(2017010227)
文摘Based on the absolute and relative gravity observations in North China from 2009 to 2014,spatial dynamic variations of the regional gravity field are obtained. We employed the Euler deconvolution method and the theoretical model to get the best estimates of parameters. Gravity field change caused by the depth and distribution in North China is calculated by back analysis. The results show the structural index that equals 1 is suitable for inversion of the gravity variation data. The inversion results indicate that the depths of anomaly field sources are spread over the Hetao fault. The research method of this paper can be used in the quantitative study on the field source and may shed new light on the interpretations of gravity change, and also provide quantitative basis for earthquake prediction index criterions based on the gravity change.
文摘Cosmological expansion or inflation is mathematically described by the theoretical notion of inverse gravity whose variations are parameterized by a factor that is a function of the distance to which cosmological expansion takes prominence over gravity. This assertion is referred to as the inverse gravity inflationary assertion. Thus, a correction to Newtonian gravitational force is introduced where a parameterized inverse gravity force term is incorporated into the classical Newtonian gravitational force equation where the inverse force term is negligible for distances less than the distance to which cosmological expansion takes prominence over gravity. Conversely, at distances greater than the distance to which cosmological expansion takes prominence over gravity. The inverse gravity term is shown to be dominant generating universal inflation. Gravitational potential energy is thence defined by the integral of the difference (or subtraction) between the conventional Newtonian gravitational force term and the inverse gravity term with respect to radius (r) which allows the formulation, incorporation, and mathematical description to and of gravitational redshift, the Walker-Robertson scale factor, the Robinson-Walker metric, the Klein-Gordon lagrangian, and dark energy and its relationship to the energy of the big bang in terms of the Inverse gravity inflationary assertion. Moreover, the dynamic pressure of the expansion of a cosmological fluid in a homogeneous isotropic universe is mathematically described in terms of the inverse gravity inflationary assertion using the stress-energy tensor for a perfect fluid. Lastly, Einstein’s field equations for the description of an isotropic and homogeneous universe are derived incorporating the mathematics of the inverse gravity inflationary assertion to fully show that the theoretical concept is potentially interwoven into the cosmological structure of the universe.
基金supported by the National Foundation of China(Grant Nos.41941016 and 42174123)China Geological Survey(Grant No.DD20221630).
文摘The Guxiang-Tongmai segment of the Jiali fault is situated northeast of the Namche Barwa Syntaxis in northeastern Xizang.It is one of the most active strike-slip faults near the syntaxis and plays a pivotal role in the examination of seismic activity within the eastern Himalayan Syntaxis.New study in the research region has yielded a 1:200000 gravity dataset covering an area 1500 km^(2).Using wavelet transform multiscale decomposition,scratch analysis techniques,and 3D gravity inversion methods,gravity anomalies,fault distributions,and density structures were determined across various scales.Through the integration of our new gravity data with other geophysical and geological information,our findings demonstrate substantial variations in the overall crustal density within the region,with the fault distribution closely linked to these density fluctuations.Disparities in stratigraphic density are important causes of variations in the capacity of geological formations to endure regional tectonic stress.Earthquakes are predominantly concentrated within the density transition zone and are primarily situated in regions of elevated density.The hanging wall stress within the Guxiang-Tongmai segment of the Jiali fault exhibits a notable concentration,marked by pronounced anisotropy,and is positioned within the density differential zone,which is prone to earthquakes.
基金supported by the National Natural Science Foundation of China (Grant No.42074092)Project of Stable Support for Youth Team in Basic Research Field,Chinese Academy of Sciences (Grant No.YSBR-020)。
文摘The South China continental margin spans various land-sea tectonic units,including the Jiangnan orogenic belt,the Cathaysia Block,and the northern margin of the South China Sea,exhibiting significant crustal structural differences.The widespread exposure of Mesozoic granites in South China reveals extensive tectonic-magmatic activities in the region.Therefore,in-depth research into the deep structure of the South China continental margin is of great significance for understanding the tectonic evolution and resource effects of the area.This paper focuses on the South China and northern South China Sea regions,employing the Hamiltonian Monte Carlo(HMC) three-dimensional density gravity inversion method,combined with deep seismic sounding and ocean bottom seismometer data,to establish a three-dimensional density model covering the land-sea extent of the South China continental margin.The density structure reveals Moho depths of 28-48 km in the South China continent,22-28 km in the northern margin of the South China Sea,and 10-20 km in the northwestern sub-basin,with the Moho surface rising from land to sea.Based on the density characteristics of granites in the region,the possible distribution ranges of granite bodies are delineated.The results show that the bottom boundaries of the Miaoershan-Yuechengling and Zhuguangshan-Wanyangshan granite bodies extend approximately 12-15 km,while the bottom boundaries of the Fogang and Darongshan-Shiwandashan granite bodies are at depths of about 4-5 km.The crustal structure of the South China continental margin thickens from sea to land,superimposed with local crustal thinning,reflecting the complex tectonic changes of the South China continent and the comprehensive influence of multi-phase tectonic-magmatic activities.The depth distribution of large granite bodies inferred from the density structure provides a basis for exploring deep tectonic-magmatic activities and their impact on mineralization in the region.
基金Open Fund of Hubei Luojia Laboratory(No.220100033)National Natural Science Foundation of China(Nos.42174108,42192535,42242015)。
文摘Gravity field is the most basic physical field generated by the material properties of the Earth system.It reflects the spatial distribution,movement and change of materials determined by the interaction and dynamic process inside the Earth.Over the years,a variety of technical means have been used to detect the Earth’s gravity field and supported numerous studies on the global change,resource detection,geological structure movement,water resources change and other related fields of research.Here is part of the progress in surface and marine gravimetry obtained by Chinese geodesy scientists from 2019 to 2023 from the following aspects,including:①Continuous gravity network in Chinese mainland;②Application of superconducting gravity measurement;③Network adjustment for continental-scale gravity survey campaign and data quality control;④Regional time-variable gravity field and its application;⑤Research progress on novel technologies for gravity inversion;⑥Research progress on marine gravity field determination;⑦Application research on marine gravity field.
基金This research was jointly funded by the National Key R&D Program of China(No.2021YFA0715101)the National Natural Science Foundation of China(Nos.41974101 and 41774098)the MOST Special Fund from the State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences.We thank the two anonymous reviewers and the associate editor for their precious comments and suggestions。
文摘The southern segment of the North-South Seismic Belt in China is a critical region for earthquake preparedness and risk reduction efforts.However,limited by the low density of seismic stations and the use of single-parameter physical structural models,the deep tectonic features and seismogenic environment in this area remain controversial.Thus,a comprehensive analysis based on high-resolution crustal structures and multiple physical parameters is required.In this study,we applied the ambient noise tomography method to obtain the three-dimensional(3D)crustal S-wave velocity structure using continuous waveform data from 112 permanent stations and 350 densely distributed temporary stations in the southern segment of the North-South Seismic Belt.Then,we obtained the high-resolution 3D density structure through wavenumber-domain 3D gravity imaging constrained by the velocity structure.The low-velocity and low-density anomalies in the upper crust of the study area were mainly distributed in the Sichuan Basin and around Dali and Simao,while the high-velocity and high-density anomalies were primarily distributed in the Panxi region,corresponding to the surface geological features.Two prominent low-velocity and low-density anomalies were observed in the middle and lower crust:one to the west of the Songpan-Garzêblock and Sichuan-Yunnan diamond-shaped block,and the other near the Anninghe-Xiaojiang fault.Combined with the spatial distribution of seismic events in the study area,we found that previous earthquakes predominantly occurred in the transition zones between high and low anomaly regions and in the low-velocity and low-density zones in the upper crust.In contrast,moderate-to-strong earthquakes mainly occurred within the transition zones between high and low anomaly regions and close to the high-velocity and high-density regions,often with low-velocity and low-density layers below their hypocenters.Fluids play a critical role in the seismogenic process by reducing fault strength and destabilizing the stress state,which may be a triggering factor for earthquakes in the study area.Additionally,the upwelling of molten materials from the mantle may lead to energy accumulation and stress conce-ntration,providing an important seismogenic background for moderate-to-strong earthquakes in this area.
