Imaging buried geological boundaries is one of a major objective during the interpretation of magnetic field data in Geophysics. Therefore, edge detection and edge enhancement techniques assist a crucial role on this aim. Most of the existing edge detector methods require to obtain special points such as in general the maxima of the resulting image. One of the useful tools in estimating edges from magnetic data is the tilt angle of the analytical signal amplitude due to its value slightly dependence on the direction of magnetization. In this study, the maxima of the tilt angle of analytical signal amplitudes of the magnetic data was determined by a curvature-based method. The technique is based on fitting a quadratic surface over a 3×3 windows of the grid for locating any appropriate critical point that is near the centre of the window. The algorithm is built in Matlab environment. The feasibility of the algorithm is demonstrated in two cases of synthetic data as well as on real magnetic data from Tu Chinh-Vung May area. The source code is available from the authors on request.ReferencesAkpınar Z., Gürsoy H., Tatar O., Büyüksaraç A., Koçbulut F., Piper, JDA., 2016. Geophysical analysis of fault geometry and volcanic activity in the Erzincan Basin, Central Turkey, Complex evolution of a mature pull-apart basin. Journal of Asian Earth Sciences, 116, 97-114. Beiki M., 2010. Analytic signals of gravity gradient tensor and their application to estimate source location, Geophysics, 75(6), 159-174.Blakely R. J., and Simpson R.W., 1986. Approximating edges of source bodies from magnetic or gravity anomalies, Geophysics, 51, 1494-1498.Chen An-Guo, Zhou Tao-Fa, Liu Dong-Jia, Zhang Shu, 2017. Application of an enhanced theta-based filter for potential field edge detection: a case study of the LUZONG ORE DISTRICT, Chinese Journal of Geophysics, 60(2), 203-218.Cooper G.RJ., 2014. Reducing the dependence of the analytic signal amplitude of aeromagnetic data on the source vector direction, Geophysics, 79, 55-60.Cordell L., 1979. Gravimetric Expression of Graben Faulting in Santa Fe Country and theEspanola Basin, New Mexico. In Ingersoll, R.V., Ed., Guidebook to Santa Fe Country, New Mexico Geological Society, Socorro, 59-64.Cordell L and Grauch V.J.S., 1985. Mapping Basement Magnetization Zones from Aeromagnetic Data in the San Juan Basin, New Mexico, The Utility of Regional Gravity and Magnetic Anomaly Maps, Society of Exploration Geophysicists, Tulsa, 181-197.Hsu S.K., Coppense D., Shyu C.T., 1996. High- resolution detection of geologic boundaries from potential field anomalies: An enhanced analytic signal technique, Geophysics, 61, 1947-1957.Le D.C., Application of seismic exploration methods to identify geological structural characteristics supporting for hydrocarbon potential assessment in TuChinh - Vung May basin, Ph.D. Thesis, Hanoi University of Mining and Geology.Li X., 2006. Understanding 3D analytic signal amplitude: Geophysics, 71(2), 13-16.Miller H.G. and Singh V., 1994. Potential Field Tilt a New Concept for Location of Potential Field Sources, Journal of Applied Geophysics, 32, 213-217.Nabighian M.N., 1972. The analytic signal of two-dimensional magnetic bodies with polygonal cross-section: Its properties and use of automated anomaly interpretation, Geophysics, 37, 507-517.Nguyen N.T., Bui V.N., Nguyen T.T.H., 2014. Determining the depth to the magnetic basement and fault systems in Tu Chinh - Vung May area by magnetic data interpretation, Journal of Marine Science and Technology, 14(4a), 16-25.Nguyen X.H, San T.N, Bae W., Hoang M.C, 2014. Formation mechanism and petroleum system of tertiary sedimentary basins, offshore Vietnam, Energy Sources, Part A, 36, 1634-1649.Phillips J.D., Hansen R.O. and Blakely R.J., 2007. The use of curvature in potential-field interpretation, Exploration Geophysics, 38(2), 111-119.Rao D.B., and Babu N.R., 1991. A rapid method for three-dimensional modeling of magnetic anomalies, Geophysics, 56(11), 1729-1737.Roest W.R., Verhoef J., and Pilkington M., 1992. Magnetic interpretation using the 3-D analytic signal, Geophysics, 57, 116-125.Tran N., 2017. Sediment geology of Vietnam, VNU Press.Tran T.D., Tran N., Nguyen T.H., Dinh X.T., Pham B.N., Nguyen T.T., Tran T.T.T.N., Nguyen T.H.T., 2018. The Miocenedepositional geological evolution of Phu Khanh, Nam Con Son and Tu Chinh - Vung May basins in Vietnam continental shelf, VNU Journal of Science: Earth and Environmental Sciences, 34(1), 112-135.Vo T.S., Le H.M., Luu V.H., 2005. Three-dimensional analytic signal method and its application in interpretation of aeromagnetic anomaly maps in the Tuan Giao region, Proceedings of the 4th geophysical scientific and technical conference of Vietnam, Publisher of Science and Engineering 2005.Wijns C, Perez C and Kowalczyk P, 2005, Theta map: Edge detection in magnetic data, Geophysics, 70, 39-43.
This study attempts to estimate the thermal structure in the Southern Vietnam continental shelf by calculating the Curie point depth isotherm using magnetic data. The Curie point depth values, from 49 overlapping blocks 128 × 128 km in size, have been estimated by the exponential approach. This approach is based on the analytical solution of the exponential equations obtained from transforming the magnetic anomaly data into the frequency domain. According to the obtained results, the range of Curie point depths is from 15.3 to 35.6 km. In the study area, the greatest Curie point depth is located in the South-Eastern part, and the smallest depth is located at North-Western part. The heat flows derived from the Curie point depths are also presented. The obtained results are at relatively high resolutions and in agreement with the published information available for the study area. The Curie point depths generally lie below the Moho surface in this region but lie above in some locations, notably the Cuu Long basin.
The study was conducted with the goal of improving tax compliance of taxpayers (NNT) at the Tax Department of Long An Province. With a sample of 204 taxpayers at the Long An Provincial Tax Department selected on a random basis having transactions with the Long An Provincial Tax Department in 2019 and with the support of SPSS software 22. Factor analysis EFA and multiple regression analysis were used in the study. The research results show that 7 factors affecting tax compliance of taxpayers in Long An province are: (i) PLCS - Tax laws and policies; (ii) DDNNT: Characteristics of taxpayers; (iii) NKD: Business lines; (iv) KT: Economic factors; (v) TL: Psychological factors; (vi) CQQLT: QLT Agency; and (vii) XH: Social factors. Thereby, giving some specific solutions and recommendations to enhance tax compliance of taxpayers in Long An province in the coming time.
This paper presents a comparative study of effectiveness of edge detection methods such as total horizontal gradient, analytic signal amplitude, tilt angle, gradient amplitude of tilt angle, theta map, horizontal tilt angle, tilt angle of total horizontal gradient, tilt angle of analytic signal, improved theta map, and total horizontal gradient of improved tilt angle. The effectiveness of each method was estimated on synthetic magnetic data and synthetic gravity anomaly data with and without noise. The obtained results show that the tilt angle of gradient amplitude can detect all the edges more clearly and precisely. The applicability of each method is demonstrated on the aeromagnetic anomaly data from the Zhurihe region of Northeast China, and Bouguer gravity anomaly data from a region of North Vietnam. The results computed by the tilt angle of horizontal gradient were also in accord with the geologic structures of the areas.
In this paper, we present an improved algorithm based on Murthy and Rao’s algorithm to invert magnetic anomalies of two-dimensional basement structures. Here, the magnetic basement interface is approximated by a 2N-sided polygon with assumption that the bottom of the basement is the Curie surface. The algorithm is built in Matlab environment. The model testing shows that the proposed method can perform computations with fast and stable convergence rate. The obtained result also coincide well with the actual model depth. The practical applicability of the method is also demonstrated by interpreting three magnetic profiles in the southeast part of the continental shelf of Vietnam.
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