EXPLORING FOR STRATIGRAPHIC TRAPS WITH GRAVITY GRADIENTS

Geophysics ◽  
1975 ◽  
Vol 40 (2) ◽  
pp. 256-268 ◽  
Author(s):  
Sigmund Hammer ◽  
Rodolfo Anzoleaga
Keyword(s):  
Gradient Method ◽  
Torsion Balance ◽  
Important Application ◽  
Theory And Practice ◽  
Horizontal Gradient ◽  
Gravity Gradients ◽  
Limited Extent ◽  
Field Surveys ◽  
New Instrumentation ◽  
Vertical Gradients

The vast and growing literature on the search for stratigraphic traps for petroleum ignores gravity gradients, for which the theory has been available since the heyday of the Eötvös torsion balance decades ago. These are discussed in this paper. The horizontal and vertical gradients can be measured with available gravimeters and (to a limited extent) with the Eötvös torsion balance. A major advantage of the gradient method is that surveying to determine position and elevation of the station is not required. Both theory and practice have been reported in the geophysical literature, but the important application to stratigraphic traps has not been mentioned. We evaluate here the method for locating “pinchouts”, a term which embraces “stratigraphic” and “unconformity” traps in Halbouty’s (1972) classification. Both position and depth of the assumed pinchout are determined by the gradient anomaly. The magnitudes of anomalies of horizontal and vertical gradients are about equal. However, pending new instrumentation, only the horizontal gradient is practically useful for field surveys. The gradient method is quantitatively promising and, used in conjunction with other methods, should significantly advance the search for stratigraphic traps for petroleum.

GRAVITY GRADIENTS AND THE INTERPRETATION OF THE TRUNCATED PLATE

Geophysics ◽  
1976 ◽  
Vol 41 (6) ◽  
pp. 1370-1376 ◽  
Author(s):  
John M. Stanley ◽  
Ronald Green
Keyword(s):  
Hilbert Transform ◽  
Theoretical Data ◽  
Vertical Gradient ◽  
Density Contrast ◽  
Horizontal Gradient ◽  
Gravity Gradients ◽  
Gravity Method ◽  
Commercially Important ◽  
Dip Angle ◽  
Vertical Gradients

The truncated plate and geologic contact are commercially important structures which can be located by the gravity method. The interpretation can be improved if both the horizontal and vertical gradients are known. Vertical gradients are difficult to measure precisely, but with modern gravimeters the horizontal gradient can be measured conveniently and accurately. This paper shows how the vertical gradient can be obtained from the horizontal gradient by the use of a Hilbert transform. A procedure is then presented which easily enables the position, dip angle, depth, thickness, and density contrast of a postulated plate to be precisely and unambiguously derived from a plot of the horizontal gradient against the vertical gradient at each point measured. The procedure is demonstrated using theoretical data.

Relative precision of vertical and horizontal gravity gradients measured by gravimeter

Geophysics ◽  
1979 ◽  
Vol 44 (1) ◽  
pp. 99-101 ◽  
Author(s):  
Sigmund Hammer
Keyword(s):  
Survey Data ◽  
Hilbert Transform ◽  
Gravity Data ◽  
Gradient Methods ◽  
Vertical Gradient ◽  
Gravity Gradients ◽  
Relative Precision ◽  
The Hilbert Transform ◽  
Vertical Gradients ◽  
Vertical Gradient Of Gravity

Several recent publications advocate the use of the vertical gradient of gravity from gravimeter measurements at two elevations in a portable tower (Thyssen‐Bornemisza, 1976; Fajklewicz, 1976; Mortimer, 1977). Contrary opinions have also been expressed (Hammer and Anzoleaga, 1975; Stanley and Green, 1976; Thysen‐Bornemisza, 1977; Arzi, 1977). The disagreement revolves around the question of practically attainable precision of the vertical gradient tower method. Although it is possible to calculate both horizontal and vertical gradients from conventional gravity survey data by use of the Hilbert transform (Stanley and Green, 1976), it should be noted that highly precise gravity data are required. Also the need for connected elevation and location surveys, the major cost in gravity surveying, is not avoided. This is a significant advantage of the gradient methods. The purpose here is to present a brief consideration of the relative precision of the horizontal and vertical gradients, as measured in the field by special gravimeter observations.

Limitations of determining density or magnetic boundaries from the horizontal gradient of gravity or pseudogravity data

Geophysics ◽  
1987 ◽  
Vol 52 (1) ◽  
pp. 118-121 ◽  
Author(s):  
V. J. S. Grauch ◽  
Lindrith Cordell
Keyword(s):  
Gradient Method ◽  
Gravity Data ◽  
Magnetic Data ◽  
Horizontal Gradient ◽  
Maximum Magnitude ◽  
Gridded Data ◽  
Fourier Techniques ◽  
Gradient Magnitude ◽  
Vertical Fault ◽  
Over The Top

The horizontal‐gradient method has been used since 1982 to locate density or magnetic boundaries from gravity data (Cordell, 1979) or pseudogravity data (Cordell and Grauch, 1985). The method is based on the principle that a near‐vertical, fault‐like boundary produces a gravity anomaly whose horizontal gradient is largest directly over the top edge of the boundary. Magnetic data can be transformed to pseudogravity data using Fourier techniques (e.g., Hildenbrand, 1983) so that they behave like gravity data; thus the horizontal gradient of pseudogravity also has maximum magnitude directly over the boundary. The method normally is applied to gridded data rather than to profiles. The horizontal‐gradient magnitude is contoured and lines are drawn or calculated (Blakely and Simpson, 1986) along the contour ridges. These lines presumably mark the top edges of magnetic or density boundaries. However, horizontal‐gradient magnitude maxima (gradient maxima) can be offset from a position directly over the boundary for several reasons. Offsets occur when boundaries are not near‐vertical, or when several boundaries are close together. This note predicts these offsets. Many other factors also cause offsets, but they are less straightforward and usually are only significant in local studies; we discuss these factors only briefly.

scholarly journals Insights into thermal preferences of copepods in nature using the horizontal gradient method

2017 ◽  
Vol 39 (5) ◽  
pp. 849-859 ◽  
Author(s):  
V. B. Verbitsky ◽  
V. I. Lazareva ◽  
E. N. Medyantseva ◽  
O. A. Malysheva ◽  
S. M. Zhdanova ◽  
...  
Keyword(s):  
Gradient Method ◽  
Horizontal Gradient ◽  
Thermal Preferences

scholarly journals A Gauss Elimination Method for estimating locations of extrema in gridded data: Applications for Potential Field Data

2020 ◽  
Author(s):  
Dung Nguyen Kim ◽  
Dung Tran Tuan
Keyword(s):  
Gradient Method ◽  
Numerical Models ◽  
Traditional Approach ◽  
Dimensional Space ◽  
Gaussian Elimination ◽  
Accurate Determination ◽  
Quadratic Functions ◽  
Horizontal Gradient ◽  
Elimination Method ◽  
New Approach

Abstract. Extrema in gravity measurements can be used to locate geological structures of interest and the boundaries of such structures can be associated with the maxima in the gradients of the gravitational field strength. Finding the extrema of measured geophysical fields measured on the Earth's surface when the data is sparse is challenging. The inferred positions of such extrema are highly model dependent. Polynomial functions of two variables can be fitted to the data. Higher order polynomials typically give more accurate determination of the extrema, but the maximum order of the polynomial is limited by the number of data points. Difficulties are accentuated in the vicinity of boundaries of the existing data. The maximum horizontal gradient method has often been applied in this context. But in that particular construction, quadratic functions are developed in each dimension. Although the magnitudes of the extracted coefficients are obtained from three points related by their positions on orthogonal straight lines, off axis information should be included as well. The present paper introduces a modification of the maximum horizontal gradient method to overcome these difficulties. A Function f of the two variables x and y: f(x,y) = a1x2 + a2y2 + a3x2y2 + a4x2y + a5xy2 + a6xy + a7x + a8y + a9 is established by Gaussian elimination method base on a 3x3 neighborhood data grid. An extract creates a 4-dimensional space based on 4 specific cases of function f, including x = 0, y = 0, y = −x and y = x, they are four functions of one variable. The extreme points position are detected from these functions of one variable. To prove the proposed theoretical basis, as well as the built computer program, the paper presents two numerical models. The obtained results shown that the new approach has more maxima points than the traditional approach. Beside advantages of new approach, some disadvantages is also discussed in this paper. Moreover, we conclude with the application of our new approach to gravitational data in the East Vietnam Sea and demonstrate that we thereby disclose the existence of a gravity trench undetectable in the traditional method.

De gedroomde verbondenheid van wetenschap en praktijk in de organisatiepsychologie

2004 ◽  
Vol 17 (5) ◽  
Author(s):  
Ben J.M. Emans
Keyword(s):  
Tacit Knowledge ◽  
Organizational Psychology ◽  
Theory And Practice ◽  
Theory Construction ◽  
Limited Extent ◽  
Traditional Research ◽  
Linking Theory And Practice ◽  
The Relationship

Dreaming of linking theory and practice in organizational psychology Dreaming of linking theory and practice in organizational psychology Ben J.M. Emans, Gedrag & Organisatie, Volume 17, October 2004, nr. 5, pp. 310-326 The relationship between the worlds of scholars and practitioners in the field of organizational psychology is affected by the different objectives that both worlds state for theory construction. This paper argues that these differences – which involve issues addressed, concepts used, statements and underlying assumptions – may be large, but at the same time in no sense fundamental. Two research approaches for bridging the resulting gap between research theory and practice are discussed. The first approach is based on the postmodern/constructionist formula, the second on the formula of elicitation of the practitioners' tacit knowledge. The first approach is assessed as being helpful only to a limited extent as it tends to impede generalizing, whereas the second is found to constitute a fruitful approach as an addition to more traditional research approaches.

THE AVERAGE HORIZONTAL GRAVITY GRADIENT

Geophysics ◽  
1962 ◽  
Vol 27 (5) ◽  
pp. 714-715
Author(s):  
Stephen Thyssen‐Bornemisza ◽  
W. F. Stackler
Keyword(s):  
Gravity Gradient ◽  
Horizontal Gradient ◽  
Theoretical Discussion ◽  
Gravity Gradients ◽  
Geophysical Exploration

The authors reported experiments of making measurements with the gravity meter at close spacings (Geophysics, 1956, 1958; Journal ASPG, 1960, 1962) for the purpose of obtaining gravity gradients and micro‐gravimetric maps. Since the average horizontal gradient seems to be of some interest for geophysical exploration, a brief theoretical discussion is presented.

MAGNETIC SURVEYING USING HORIZONTAL GRADIENT VECTORS

Geophysics ◽  
1977 ◽  
Vol 42 (6) ◽  
pp. 1262-1264 ◽  
Author(s):  
S. Thyssen‐Bornemisza
Keyword(s):  
Magnetic Field ◽  
Unit Vector ◽  
Magnetic Potential ◽  
Horizontal Gradient ◽  
Magnetic Intensity ◽  
Total Field ◽  
Nonlinear Characteristics ◽  
Normal Magnetic Field ◽  
Vertical Gradients ◽  
Airborne Magnetic

It was pointed out some time ago (Bhattacharyya, 1965) that the total intensity anomaly of a magnetic field ΔT in the direction of the normal magnetic field of earth is expressed by the equation, [Formula: see text]Here ΔV denotes the anomaly of the magnetic potential and t the unit vector in the direction of earth’s undisturbed total field. Horizontal and vertical gradients observed along the tracks of airborne magnetic surveys were discussed by several authors (Wickerham, 1954; Glicken, 1955; Hood, 1965; Langan, 1966). These gradients are obtained from the formulas [Formula: see text] [Formula: see text]where the magnetic intensity differences are observed over horizontal and vertical intervals Δx and Δz between two sensors. However, this approach is only valid when the depth h of the causative body or structure is relatively large compared to Δx and Δz; thus in cases of shallow anomalies, the nonlinear characteristics of the anomalous magnetic field would distort the observed gradients and render interpretation of data very difficult.

INSTRUMENTAL ARRANGEMENT TO MEASURE GRAVITY WITH GRADIENTS

Geophysics ◽  
1970 ◽  
Vol 35 (4) ◽  
pp. 713-715 ◽  
Author(s):  
Stephen Thyssen‐Bornemisza
Keyword(s):  
Gravitational Field ◽  
Theoretical Solution ◽  
Gravitational Acceleration ◽  
Gravity Gradients ◽  
Practical Application ◽  
Measuring Device ◽  
Inverse Process ◽  
Vertical Gradients

Every mass generates gravity gradients in addition to the gravitational field itself; this fact suggests that vertical gradients may be determined with a gravity measuring device based on a two‐level observation technique (Hammer, 1938; Thyssen‐Bornemisza, 1944). The inverse process, i.e. measurement of gravity or gravitational acceleration with the help of vertical gradients, apparently has not been investigated. Of course, gravity values can be computed from vertical gradients by integration (Paterson, 1961), but to actually measure gravity with vertical gradients is quite a different problem. The theoretical solution presented here provides the background for possible practical application.

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