On: “Geophysical Analysis in Central Indiana using Potential Field Continuation,” by A. J. Rudman, Judson Mead, Joseph F. Whaley, and Robert F. Blakely (GEOPHYSICS, October 1971, p. 878–890)

Geophysics ◽  
1972 ◽  
Vol 37 (6) ◽  
pp. 1047-1047
Author(s):  
Douglas J. Guion
Keyword(s):  
Gravity Anomaly ◽  
Magnetic Anomaly ◽  
Potential Field ◽  
Downward Continuation ◽  
Gravity Effect ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Anomaly ◽  
Field Continuation ◽  
Hamilton County

I read with interest the article concerning modeling the Hamilton County, Indiana, gravity and magnetic anomaly. The authors’ method for outlining the igneous body by downward continuation aroused my curiosity to the point that I decided to study the results in detail. My investigation revealed that the calculated gravity effect of the model did not satisfy the observed gravity anomaly. In fact, the amount of mismatch is quite serious.

North American Gravity and Magnetic Anomaly Workshops

Geophysics ◽  
1981 ◽  
Vol 46 (11) ◽  
pp. 1611-1617
Author(s):  
W. J. Hinze ◽  
N. W. O’Hara ◽  
M. S. Reford ◽  
J. G. Tanner
Keyword(s):  
Gravity Anomaly ◽  
Magnetic Anomaly ◽  
North American ◽  
North American Continent ◽  
The North ◽  
Terrain Effects ◽  
Gravity And Magnetic ◽  
Anomaly Map ◽  
Map Series ◽  
Gravity And Magnetic Anomaly

The North American Gravity and Magnetic Anomaly Map Workshops, realizing the importance of regional gravity and magnetic anomalies to investigating the structure and composition of the earth, enthusiastically support the preparation of North American gravity and magnetic anomaly maps. Sufficient magnetic and gravity anomaly data are available over the North American continent, the Caribbean, and adjacent marine areas to produce geologically meaningful maps. These maps will be published within the decade at a scale of 1:5 million on the same map base being used by a variety of organizations to produce other geologic/geochemical/geophysical maps in cooperation with the Geological Society of America’s Centennial Map Series. The anomaly maps will be published in color with transparent overlays also available. The gravity anomaly map will be contoured at a 10 mgal interval using Bouguer anomalies onshore corrected wherever possible and necessary for terrain effects and free‐air anomalies offshore. Existing or soon to be completed magnetic and gravity anomaly maps of Canada, the U.S., and Mexico will provide the nuclei for preparing the North American maps. Programs for producing these maps in a timely manner are organized based upon a series of committees and the cooperation of agencies of the involved North American nations.

Three-dimensional numerical modeling of gravity and magnetic anomaly in a mixed space-wavenumber domain

Geophysics ◽  
2019 ◽  
Vol 84 (4) ◽  
pp. G41-G54 ◽  
Author(s):  
Shikun Dai ◽  
Dongdong Zhao ◽  
Shunguo Wang ◽  
Bin Xiong ◽  
Qianjiang Zhang ◽  
...  
Keyword(s):  
Numerical Modeling ◽  
Fourier Transform ◽  
Differential Equations ◽  
Numerical Solution ◽  
Magnetic Anomaly ◽  
Large Scale ◽  
Vertical Component ◽  
Wavenumber Domain ◽  
Gravity And Magnetic ◽  
Gravity And Magnetic Anomaly

Fast and accurate numerical modeling of gravity and magnetic anomalies is the basis of field-data inversion and quantitative interpretation. In gravity and magnetic prospecting, the computation and memory requirements of practical modeling is still a significant issue, which leads to the difficulty of using efficient and detailed inversions for large-scale complex models. A new 3D numerical modeling method for gravity and magnetic anomaly in a mixed space-wavenumber domain is proposed to mitigate the difficulties. By performing a 2D Fourier transform along two horizontal directions, 3D partial differential equations governing gravity and magnetic potentials in the spatial domain are transformed into a group of independent 1D differential equations wrapped with different wavenumbers. Importantly, the computation and memory requirements of modeling are greatly reduced by this method. A modeling example with 4,040,100 observations can be finished in approximately 28 s on a desktop using a single core, and the independent differential equations are highly parallel among different wavenumbers. The method preserves the vertical component in the space domain, and thus a mesh for modeling can be finer at a shallower depth and coarser at a deeper depth. In general, the new method takes into account the calculation accuracy and the efficiency. The finite-element algorithm combined with a chasing method is used to solve the transformed differential equations with different wavenumbers. In a synthetic test, a model with prism-shaped anomalies is used to verify the accuracy and efficiency of the proposed algorithm by comparing the analytical solution, our numerical solution, and a well-known numerical solution. Furthermore, we have studied the balance between computational accuracy and efficiency using a standard fast Fourier transform (FFT) method with grid expansion and the Gauss-FFT method. A model with topography is also used to explore the ability of modeling topography with our method. The results indicate that the proposed method using the Gauss-FFT method has characteristics of fast calculation speed and high accuracy.

Magnetic anomaly of a circular lamina

Geophysics ◽  
1979 ◽  
Vol 44 (1) ◽  
pp. 102-107 ◽  
Author(s):  
S. K. Singh ◽  
R. Castro E. ◽  
M. Guzman S.
Keyword(s):  
Circular Cylinder ◽  
Closed Form ◽  
Gravity Anomaly ◽  
Magnetic Anomaly ◽  
Magnetic Anomalies ◽  
Hankel Transform ◽  
Poisson’S Equation ◽  
Poisson's Equation ◽  
Gravity And Magnetic

Closed form expressions for the gravity anomaly of a circular lamina and the gravity and magnetic anomalies due to a vertical right circular cylinder have been obtained previously (Singh, 1977a; Singh, 1977b; Singh and Sabina, 1978) by a method which avoids complicated integrations commonly used in deriving such solutions (e.g., Nabighian, 1962; Rao and Radhakrishnamurty, 1966). The method involves use of the Fourier‐Hankel transform of Poisson’s equation. The final expressions are obtained in closed form by employing certain tabulated integrals.

Gravity and magnetic anomalies of the Sutton Mountains region, Quebec and Vermont: expressions of rift volcanics related to the opening of Iapetus

1981 ◽  
Vol 18 (4) ◽  
pp. 680-692 ◽  
Author(s):  
P. S. Kumarapeli ◽  
A. K. Goodacre ◽  
M. D. Thomas
Keyword(s):  
Gravity Anomaly ◽  
Magnetic Anomaly ◽  
Triple Junction ◽  
Three Dimensional ◽  
Surface Expression ◽  
Magnetic Anomalies ◽  
Iapetus Ocean ◽  
Metavolcanic Rocks ◽  
Gravity And Magnetic ◽  
Narrow Belt

Prominent, nearly coincident, positive gravity and magnetic anomalies occur in the Sutton Mountains region, centered about 100 km east of Montreal, Quebec. Several lines of evidence indicate that the gravity anomaly stems from two principal sources: a deep (mid and lower crustal) source of speculative origin and a shallow source identifiable with a narrow belt of late Precambrian – early Cambrian metavolcanic rocks, the Tibbit Hill volcanics. The magnetic anomaly seems to be produced mainly by the metavolcanic rocks. Three-dimensional modelling of a residual gravity anomaly, supplemented by two-dimensional modelling of the magnetic anomaly, shows that the seemingly minor belt of metavolcanic rocks constitutes the surface expression of a thick (maximum thickness ~8 km) pile of dominantly mafic volcanics, which are only slightly exposed at the present level of erosion.The Tibbit Hill volcanics are regarded as products of rift-related volcanism that occurred at an rrr triple junction developed during the early stages of the opening of the Iapetus Ocean. The Ottawa graben is probably the failed arm of this triple junction. The emplacement of the Grenville dike swarm whose trend is nearly coincident with that of the Ottawa graben was probably coeval with the volcanism in the Sutton Mountains region. The present work shows that the volcanism in the region was on a much larger scale than hitherto recognized.

A new source location and attribute recognition method based on correlation analysis of gravity and magnetic anomaly

2020 ◽  
Author(s):  
Baoliang Lu ◽  
Tao Ma ◽  
Shengqing Xiong ◽  
Wanyin Wang
Keyword(s):  
Potential Field ◽  
Source Area ◽  
High Density ◽  
Low Density ◽  
Field Source ◽  
Geological Body ◽  
Gravity And Magnetic ◽  
Attribute Recognition ◽  
Parameter Values ◽  
Gravity And Magnetic Anomaly

<p>The traditional gravity and magnetic correspondence analysis tends to have high correlation outside the field source area. In order to overcome the disadvantage, we propose a new method for identify the source position and attribute, which is based on similarity and vertical derivative of potential field. In this method, we put forward a new gravity and magnetic correlation parameter (GMCP), which can effectively reduce the range of potential field source and indicate the field intensity information. The distribution of the non-zero areas of GMCP reflects the size of the source. GMCP discriminant parameter values of positive and negative reflect the source attribute. When GMCP is greater than zero, it is a positive correlation indicating that there are high-density and high-magnetization or low-density and low-magnetization homologous bodies in this region; When GMCP is less than zero, it is negative correlation indicating that there are high-density and low-magnetic or low-density and high-magnetic density homologous bodies in this region. GMCP goes to zero, which means no gravity-magnetic homologous geological body. Complex models test results with different noise level and actual data processing of South China Sea Basin show the correctness and validity of identification of the proposed methods.</p>

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