3D Joint inversion of gravity and gravity tensor data

The processing and interpretation of gravity and gradient data plays an important role in geophysics. The cross gradient joint inversion is usually used for achieving structure coupling of multiple geophysical mod-els.In order to realize the coupling of gravity and gravity tensor data, the authors analyzed each component. The results show that different types of data contain different direction information, and derived the joint inver-sion based on cross gradient function and applied it to model data.The theoretical model results show that the cross gradient method can reduce the multi solution and significantly improve the resolution of the inversion. The method was also applied to inverse the gravity tensor data in Vinton salt dome, showing that this method can get higher resolution results than the separate linear inversion, and be closer to the real density from drilling data.     

3 D inversion of borehole gravity data using cokriging

Borehole gravity has been used in mineral exPloration recently with the advent of slim-hole gravime-ters. It is logical to Perform inversion to utilize the information in the newly acquired data. The i...     

3D fast inversion of gravity data based on GPU

Large-scale gravity 3D interpretation depends on efficient and high-resolution 3D inversion processing of massive data.The authors applied the conjugate gradient method with minimum support function and prior model constraint to reduce multi-solutions in gravity inversion.Based on the parallel programming and compu-ting platform NVIDIA CUDA with C++language, we achieve fast 3D gravity inversion by adopting GPU parallel technique into the most time consuming part relating to sensitivity matrix.The results of theoretical model show that the abnormal body can be clearly located and the inversion speed is improved greatly.Comparing with in-version speed of the Matlab program, speed of inversion with GPU parallel technique has improved more than 100 times under the hardware condition of Geforce GTX 1060 graphics card.     

Application of gravity inversion focused in Changbai Mountain

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.     

2.5D重力双重加权聚焦反演及其应用

针对聚焦反演方法在实测数据应用中存在的趋肤效应和反演结果发散问题,设计应用深度加权和数据加权的双重加权系数灵敏度矩阵,进行核函数处理。通过反演拟合理论正演模型实验,证明了该方法的可靠性。将双重加权系数运用到山东某矿区的实测数据,反演结果清晰地反映出地下异常体的边界和深度,与剖面电阻率结果比较,两者异常位置接近,该方法可反应实际异常情况。     

Multi-component joint inversion of gravity gradient based on fast forward calculation

With the development of gravity gradient full tensor measurement technique , three-dimensional (3D) inversion based on gravity gradient tensor can provide more accurate information .But the forward calcula-tion of 3D full tensor sensitivity matrix is very time-consuming, which restricts its development and application . According to the symmetry of the kernel function , the authors reconstruct the underground source of geological body to avoid repeat computation of the same value , and work out the corresponding relationship between the re-sponse of geological body to the observation point and the response of reconstructed geological body to the obser -vation point .According to the relationship , rapid calculation of full tensor gravity sensitivity matrix can be achieved .The model calculation shows that this method can increase the speed of 30-45 times compared with the traditional calculation method .The sensitivity matrix is applied to the multi-component inversion of gravity gradient .The application of this method on the measured data provides the basis for the promotion of the meth -od.     

A new method to determine the start depth in gravity anomaly inversion

The start depth in gravity anomaly inversion is discussed in this paper, and a new method called “test comparing method” is presented to determine the start depth when both boring data and seismic data are not available. Anticline and syncline density interface models are designed to test the method; the calculated result agreed well with the designed value, which proved that the new method can be used to determine the start depth in the gravity anomaly inversion when boring data and seismic data are not available. Contribution No. 3370 from the Institute of Oceanology, Chinese Academy of Sciences. Project 49625609 supported by NSFC, and Young Scientist Lab. of Submarine Hydrothermal Activity Research.     

重力异常数据处理系统的开发与研究

利用SQL Server建立后台数据库和以面向对象的Delphi语言作为应用程序开发工具，在Windows 2000平台上开发了图形用户界面的重力异常数据处理系统。该系统集重力异常数据处理和数据库管理为一体，包括了数据输入、数据处理、数据查询、数据输出、数据库管理和系统安全管理六大功能模块。系统提供简洁的操作界面和友好的应用环境，便于用户使用。在实例运用中，将西藏地区的重力异常数据用该系统进行了处理。结果表明，系统操作简单方便．不仅能提高处理效率，还能实现对数据的系统管理。     

3D joint inversion of controlled-source audio-frequency magnetotelluric and magnetotelluric data

Different geophysical exploration methods have significant differences in terms of exploration depth, especially in frequency domain electromagnetic(EM) exploration. According to the definition of skin depth, this difference will increase with the effective detection frequency of the method. As a result,when performing three-dimensional inversion on single type of EM data, it is not possible to effectively distinguish the subsurface geoelectric structure at the full scale. Therefore, it is neces...     

Common offset ground penetrating radar data inversion based on ray theory

The authors use the common offset ground penetrating radar(GPR) data inversion based on ray theory to estimate interval velocity and to obtain the relative permittivity. In the ray-tracing based inversion, the input data are the offset distance between antennas, the velocity of the first layer, the pick-up amplitude and re-ference amplitude of each reflection layer. The thickness and velocity of each layer are calculated by this recursive method. Firstly, the horizontal homogeneous layered medium model is established, and the ideal inversion results are obtained. Subsequently, Monte Carlo method is used to establish a randomly undulating homogeneous layered medium model. The common offset GPR data for the built geological model is then simulated by finite-difference time-domain(FDTD). It proved that this ray-tracing based inversion method is feasible for the horizontal layered geological model, even the layered geological model with random undulation. Undulation, represented by RMS height and CL(correlation length), influences the inversion results. Finally, a more complex geological model--pinch-out model was established. In the pinch-out model, the pinch-out interface can be clearly identified, though there is a false anomaly, which will not significantly affect the identification of the underground medium structure.     

Several boundary identification methods of gravity data and application in Vientiane of Laos area

The authors studied the potential field boundary identification of the new technology in order to find out the possible fractures or contact zones using the following methods such as tilt derivative,horizontal deriva- tive of tilt derivative,normalized standard deviation and normalized differential method． Combined with Euler deconvolution and small subdomain filtering,the actual data processing results show that these methods are all a- ble to identify wider range extending fractures and obtain abundant geological information． The horizontal deriva- tive of tilt derivative and normalized differential method have a better resolution for the small cutting fractures and lacunae in the studied area． They provide a reliable basis for study of the cutting relationship between fractures．     

Several boundary identification methods of gravity data and application in Vientiane of Laos area

The authors studied the potential field boundary identification of the new technology in order to find out the possible fractures or contact zones using the following methods such as tilt derivative, horizontal derivative of tilt derivative, normalized standard deviation and normalized differential method. Combined with Euler deconvolution and small subdomain filtering, the actual data processing results show that these methods are all a- ble to identify wider range extending fractures and obtain abundant geological information. The horizontal derivative of tilt derivative and normalized differential method have a better resolution for the small cutting fractures and lacunae in the studied area. They provide a reliable basis for study of the cutting relationship between fractures.     

A new model of lithosphere deformation beneath the Okinawa Trough based on gravity data

The Ryukyu trench-arc system can be divided into two types according to its subduction model. The normal subduction in the northern part of the Philippine Sea plate creates a hinge sedimentary wedge with large deformation at the collision front, while the oblique subduction in the southern part gives rise to a smaller accretion with small deformation than that in the northern part. The mechanisms that cause distinction between these two types have been analysed and calculated by using gravity data based on the lithosphere rheology and the stress state of the lithosphere in the subduction boundary. The two types of subduction model are associated with the internal extension in the southern Okinawa Trough and the small extension in the northern part. The difference of the stress state between the two types of subduction model is also manifested in other tectonic features, such as topography, volcanic activity and crust movement. Modeling bathymetric and gravity data from this area suggests that the oblique subduction of low angle, together with smooth geometry of the overlying plate crust, results in small stress released on the south of the trench by the subduction plate. The intraplate faults in the southern Okinawa Trough behind the trench stand in surplus intensive stress. On the other hand, the normal subduction of high angle, together with strong undulation geometry of the overlying crust, results in more intensive stress released in the northern Ryukyu Trench than that in the south. The intraplate faults in the northern Okinawa Trough behind the northern Ryukyu Trench stand in small stress.     

Application of several potential field separation methods of gravity data in Vientiane of Laos area

Gravity data observed in geophysical surveys are the sum of potential field produced by all underground inhomogeneous geological sources with different scales, different patterns and different depths.The aim of gravity exploration is mainly to extract the meaningful local anomaly from the regional gravity anomaly which is helpful to detect the deep structure and delineate the favorable area for mineral prospecting.In this paper, several anomaly separation methods are theoretically discussed, including trend analysis method, finite element method, interpolating cut method and analytic continuation method.And, these methods are applied to achieve the delineation of potash-mine deposit in Vientiane.Through experiments, analysis and comparison, the separating result of upward continuation is shown to be satisfactory, for that can separate the ore body anomaly from the background field more effectively.Further, with the combination of the geological information and gravity anomaly, it infers four rich potash zones in the study area of Vientiane which is significant for future geological work.     

Joint inversion of magnetotelluric and fullwaveform seismic data based on alternating cross-gradient structural constraints

Magnetotelluric(MT)inversion and seismic inversion are important methods for the interpretation of subsurface exploration data,but separate inversion of MT and seismic produces ambiguous and non-unique results due to various factors.In order to achieve accurate results,the authors propose a joint inversion method of two-dimensional MT and seismic data in the frequency domain.The finite element method is used for numerical simulation of electromagnetic data in the forward modelling,and the Gauss-Newton method is used for the inversion.The 9-point-finite-difference method is used to solve the seismic wave field in the acoustic wave equation,and the inverse problem of seismic data is solved by full waveform inversion with a conjugate gradient,a simple and fast method.Cross gradient functions are used to provide constraint structure between resistivity and velocity parameters to carry out the joint inversion.The joint inversion algorithm is tested by double-rectangular model synthesis data,and the accuracy of the algorithm is verified.The results show that the joint inversion results are better than those from separate inversion.The algorithm is applied to a geophysical model of a metalliferous deposit in Jinchuan and is compared with the separate inversion results.It shows that the results obtained with joint inversion are much closer to the real model.     

Combined analysis of gravity and magnetic anomalies using normalized source strength

The traditional combined gravity and magnetic analysis uses the linear regression of the first order vertical derivative of the gravity anomaly and the reduction to the pole ( RTP) magnetic anomaly, and provides the quantitative or semi-quantitative interpretation by calculating the correlation coefficient, slope, and inter-cept.In the calculation process, due to the remanent magnetization, the RTP anomaly still contains the effect of oblique magnetization, as a result, the homologous gravity and magnetic anomalies may display irrelevant results in the linear regression calculation.To solve this problem, we present a new combined analysis using normal-ized source strength ( NSS ) .Based on the Poisson's relation, the gravity field can be transformed into the pseudomagnetic field of the direction of geomagnetic field magnetization under the homologous condition.The NSS of the pseudomagnetic field and that of the original magnetic field are calculated, which are insensitive to the remanence, and then the linear regression analysis is carried out.The approach is tested using synthetic model under complex magnetization, the results show that it can still identify the gravity and magnetic anomalies from same source under strong remanence, and can establish the Poisson's ratio.Finally, this approach is ap-plied in Wudalianchi in China.The results demonstrated that this approach is feasible and can provide the ref-erence for further data processing and interpretation.     

基于地震反演及多信息协同约束的冲积扇储层精细建模

油田开发早期区块井资料少、井距大,难以对储层进行精确描述。采用叠后地震反演数据进行沉积相研究,定量分析扇根亚相各微相,为三维沉积相模型提供地质参数;以测井数据为硬数据,采用沉积相控制、反演协同体等信息约束建立储层的泥质质量分数模型。结果表明,应用包括地震反演信息在内的多种信息进行约束建模,可以综合测井资料纵向高精度和地震资料横向高精度的优点,解决勘探开发阶段储层精细描述的问题。     

Comparative analysis of fracture identification methods based on gravity anomaly in Heilongjiang

The identification of fractures is of great importance in gravity and magnetic data processing and interpretation.In this study,four fracture identification methods are applied,and widely used in processing and analysis of the gravity anomaly,including vertical second derivative method,tilt derivative method,theta map method and normalized differential method,for gravity data acquired in a given area in Heilongjiang.By comparing the distribution of the zero contour or maximum contour,we summarize the application effects,and both advantages and disadvantages of each method.It is found that tilt derivative method and normalized differential method provide better effects than other two methods:the narrower anomaly gradient belt and higher identification precision of fracture or geological boundary.The inferred fractures and geological boundaries have a great match with the results obtained from geologic map and remote sensing data interpretation.Those study results have definitely provided the theoretical foundation for identifying faults and the geological boundaries.     

Tectonics of the Indo-Australian plate near the Ninetyeast Ridge constrained from marine gravity and magnetic data

Although the Indo-Australian plate near the Ninetyeast Ridge is important for understanding the formation of new plate boundaries, its tectonic problems are complex and most of them are poorly known. This paper made a detailed tectonic analysis based on the data of bathymetry, gravity and magnetics. Bathymetry and gravity maps show morphological features of many folds, which are related to the intraplate deformation of the Indo-Australian plate due to the collision between the Indian and Asian plates. Gravity anomalies show the structure of fracture zones, which are caused by the seafloor spreading and transform faulting. The characteristics of the folds and fracture zones are consistent with the hypothesis that diffuse plate boundaries and redefined plate components would occur within the Indo-Australian plate. In addition, compiled magnetic data demonstrate magnetic lineations, abandoned spreading centers, southward ridge jumps and plate motions. These features provide useful information for rebuilding the tectonic evolution history of the study area. Magnetic anomalies suggest that an additional plate boundary of transform fault type is developing.