scholarly journals Gravity terrain correction for mainland territory of Vietnam

2017 ◽  
Vol 17 (4B) ◽  
pp. 145-150
Author(s):  
Pham Nam Hung ◽  
Cao Dinh Trieu ◽  
Le Van Dung ◽  
Phan Thanh Quang ◽  
Nguyen Dac Cuong
Keyword(s):  
Gravity Data ◽  
Computing Time ◽  
Terrain Correction ◽  
Bouguer Gravity ◽  
Mountainous Region ◽  
Terrain Effect ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Gravity Map

Terrain corrections for gravity data are a critical concern in rugged topography, because the magnitude of the corrections may be largely relative to the anomalies of interest. That is also important to determine the inner and outer radii beyond which the terrain effect can be neglected. Classical methods such as Lucaptrenco, Beriozkin and Prisivanco are indeed too slow with radius correction and are not extended while methods based on the Nagy’s and Kane’s are usually too approximate for the required accuracy. In order to achieve 0.1 mGal accuracy in terrain correction for mainland territory of Vietnam and reduce the computing time, the best inner and outer radii for terrain correction computation are 2 km and 70 km respectively. The results show that in nearly a half of the Vietnam territory, the terrain correction values ≥ 10 mGal, the corrections are smaller in the plain areas (less than 2 mGal) and higher in the mountainous region, in particular the correction reaches approximately 21 mGal in some locations of northern mountainous region. The complete Bouguer gravity map of mainland territory of Vietnam is reproduced based on the full terrain correction introduced in this paper.

Improvement of the conic prism model for terrain correction in rugged topography

Geophysics ◽  
1981 ◽  
Vol 46 (7) ◽  
pp. 1054-1056 ◽  
Author(s):  
Raymond J. Olivier ◽  
Réjean G. Simard
Keyword(s):  
Gravity Anomalies ◽  
Terrain Correction ◽  
Field Calculation ◽  
Bouguer Gravity ◽  
New Model ◽  
Gravity Station ◽  
Rugged Terrain ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Prism Model

Terrain corrections for Bouguer gravity anomalies are generally obtained from topographic models represented by flat‐topped compartments of circular zones, utilizing the so‐called Hayford‐Bowie (1912), or Hammer’s (1939) method. Some authors have introduced improved relief models for taking uniform slope into consideration (Sandberg, 1958; Kane, 1962; Takin and Talwani, 1966; Campbell, 1980). We present a new model that increases the accuracy of the calculation of terrain correction close to the gravity station in rugged terrain, especially when conventional templates with few zones are used in field calculation.

REDUCTION OF MAGNETIC AND GRAVITY DATA ON AN ARBITRARY SURFACE ACQUIRED IN A REGION OF HIGH TOPOGRAPHIC RELIEF

Geophysics ◽  
1977 ◽  
Vol 42 (7) ◽  
pp. 1411-1430 ◽  
Author(s):  
B. K. Bhattacharyya ◽  
K. C. Chan
Keyword(s):  
Magnetic Field ◽  
Integral Equation ◽  
Gravity Data ◽  
Analytical Relationship ◽  
Surface Distribution ◽  
Anomalous Field ◽  
Terrain Effect ◽  
Gravity Map ◽  
Finite Extent ◽  
Topographic Relief

The problem of reduction of magnetic and gravity data, when observed on an arbitrary surface in a region of high topographic relief, is studied with equivalent source representation at the points of observation. It is shown that the analytical relationship between the total magnetic field or the gravity effect and equivalent magnetization or density on an arbitrary observational surface is given by a Fredholm integral equation of the second kind. A rapidly convergent iterative scheme is described for the solution of the integral equation, yielding the surface distribution of magnetization or density. With this distribution, the field at any other surface can be easily computed. Then it has been demonstrated with model examples that the gravity or magnetic field observed on a rough terrain can be accurately reduced to a horizontal plane for processing and interpretation. A new method has been suggested for minimization of terrain‐induced anomalies on a magnetic or gravity map. This method is based on the concept that when the anomalous field observed on an arbitrary surface is continued to a surface parallel to the topography, the terrain effect in the continued field is sharply reduced relative to the field created by bodies of finite extent in the crust. Model examples are presented to show the accuracy and reliability of the method.

scholarly journals New Bouguer Gravity Maps of Venezuela: Representation and Analysis of Free-Air and Bouguer Anomalies with Emphasis on Spectral Analyses and Elastic Thickness

2012 ◽  
Vol 2012 ◽  
pp. 1-15 ◽  
Author(s):  
Javier Sanchez-Rojas
Keyword(s):  
Gravity Data ◽  
Bouguer Anomaly ◽  
Geodetic Reference System ◽  
Bouguer Gravity ◽  
Free Air ◽  
Data Compilation ◽  
Regional Tectonic ◽  
Moho Depths ◽  
Free Air Anomaly ◽  
Gravity Map

A new gravity data compilation for Venezuela was processed and homogenized. Gravity was measured in reference to the International Gravity Standardization Net 1971, and the complete Bouguer anomaly was calculated by using the Geodetic Reference System 1980 and 2.67 Mg/m3. A regional gravity map was computed by removing wavelengths higher than 200 km from the Bouguer anomaly. After the anomaly separation, regional and residual Bouguer gravity fields were then critically discussed in term of the regional tectonic features. Results were compared with the previous geological and tectonic information obtained from former studies. Gravity and topography data in the spectral domain were used to examine the elastic thickness and depths of the structures of the causative measured anomaly. According to the power spectrum analysis results of the gravity data, the averaged Moho depths for the massif, plains, and mountainous areas in Venezuela are 42, 35, and 40 km, respectively. The averaged admittance function computed from the topography and Free-Air anomaly profiles across Mérida Andes showed a good fit for a regional compensation model with an effective elastic thickness of 15 km.

scholarly journals Gravity Study using Multi-2.5D Modeling and 3D Presentation for Al Ma'aniyah Depression, Southwest of Iraq

2021 ◽  
Vol 54 (2D) ◽  
pp. 113-124
Author(s):  
Ali M. Al-Rahim
Keyword(s):  
Gravity Data ◽  
Depth Map ◽  
Bouguer Gravity ◽  
Free Air ◽  
Exact Boundary ◽  
Power Spectrum Method ◽  
Basement Depth ◽  
3D Presentation ◽  
Free Air Gravity ◽  
Gravity Map

Tectonic depression area within and/or beside widespread basin is regarded as an important location for sub-basin sedimentary sequence of Iraq which may represent an excellent accumulation of bounded sediments. Al-Ma'aniyah depression, southwest Iraq is one of such type of sub-basin. Free-air gravity data show a NS extend of this depression inside Saudi Arabia. This work focuses on studying and multi-2.5D model creation for the depression in the Iraqi territory part using Bouguer gravity data and mapping its basement relief. Firstly, the exact boundary of the depression was outlined utilizing the Free-Air gravity data. Then, a precise selection of regional field for the study area was determined by using the power spectrum method, which accordingly defines the residual anomalies that could represent structural enclosures. Many positive anomalies were assigned and enhanced using vertical and total horizontal derivatives, where they were interpreted as basement-related features. Subsequently, a 2.5D multi modeling and depth inversion for the Bouguer gravity data were accomplished by converting the gravity map to a stacked profiles depth map. A nineteen gravity profiles, which cover the study area, were modeled by assuming 2D intra-sedimentary bodies. These bodies were best presented by a 3D view that clarifies the nature of the subsurface modeled structures. The modeling shows an extra density at the northern part of the depression, in contrast, it suggests low density bodies at its southern part, the case that appears inconsistent with a previously performed magnetic interpretation. The inversion of gravity data shows that the basement depth at Al-Ma'aniyah depression ranges from 7.5 to10 km.

scholarly journals The Gravity Effect of Topography: A Comparison among Three Different Methods

2021 ◽  
Author(s):  
Carlo Iapige De Gaetani ◽  
Anna Maria Marotta ◽  
Riccardo Barzaghi ◽  
Mirko Reguzzoni ◽  
Lorenzo Rossi
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
Gravitational Effect ◽  
Terrain Correction ◽  
Bouguer Anomalies ◽  
Terrain Effect ◽  
Data Points ◽  
The One ◽  
Sharp Corners

In this paper, three different methods for computing the terrain correction have been compared. The terrain effect has been accounted for by using the standard right parallelepiped closed formula, the spherical tesseroid and the flat tesseroid formulas. Particularly, the flat tesseroid approximation is obtained by flattening the top and the bottom sides of the spherical tesseroid. Its gravitational effect can be computed as the gravitational effect of a polyhedron, i.e. a three-dimensional body with flat polygonal faces, straight edges and sharp corners or vertices. These three methods have been applied in the context of a Bouguer reduction scheme. Two tests were devised in the Alpine area in order to quantify possible discrepancies. In the first test, the terrain correction has been evaluated on a grid of points on the DTM. In the second test, Bouguer gravity anomalies were computed on sparse observed gravity data points. The results prove that the three methods are practically equivalent even in an area of rough topography though, in the second test, the Bouguer anomalies obtained by using the tesseroid and the flat tesseroid formulas have slightly smaller RMSs than the one obtained by applying the standard right parallelepiped formula.

Gravimetric terrain corrections by triangular‐element method

Geophysics ◽  
1990 ◽  
Vol 55 (2) ◽  
pp. 232-238 ◽  
Author(s):  
X. Zhou ◽  
B. Zhong ◽  
X. Li
Keyword(s):  
Simple Formula ◽  
Gravity Data ◽  
High Accuracy ◽  
Rectangular Prism ◽  
Triangular Element ◽  
Volume Integral ◽  
Correction Process ◽  
Rugged Topography ◽  
Terrain Corrections ◽  
Element Method

Terrain corrections for gravity data are a critical concern in rugged topography, because the magnitude of the corrections may be large relative to the anomalies of interest. The terrain‐correction process, however, is very tedious. At present, rectangular prism and fan‐shaped prism methods are commonly used for the corrections; but these methods assume elements have horizontal tops, an assumption which does not reflect true topography, especially near the station. A triangular‐element method which allows dipping surfaces has been developed using a Gaussian formulation to improve the correction process. This method involves a simple formula employing a surface rather than a volume integral for computing the terrain corrections with high accuracy.

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