Perturbing effects of sub-lithospheric mass anomalies in GOCE gravity gradient and other gravity data modelling: Application to the Atlantic-Mediterranean transition zone

Gravity gradient profiles across subsurface structures that are approximately 2-D contain diagnostic information regarding depth, size, and structure (geometry). Gradient space plots, i.e., plots of horizontal gradient versus vertical gradient, present the complete magnitude and phase information in the gradient profiles simultaneously. Considerable previous work demonstrates the possibility for complete structural interpretation of a truncated plate model from the gradient space plot. The qualitative and quantitative diagnostic information contained in gradient space plots is general, however. Examination of the characteristics of gradient space plots reveals that 2-D structures are readily classified as extended or localized. For example, the truncated plate model is an extended model, while the faulted plate model is a localized model. Comparison of measured or calculated gradient space plots to a model gradient space plot catalog allows a rapid, qualitative determination of structure or geometry. “Corners” of a polygonal cross‐section model are then determined as profile points corresponding to maxima on the vertical gradient profile. A generalized approach to structural interpretation from gravity data consists of (1) determining vertical and horizontal gradient profiles perpendicular to the strike of a 2-D gravity anomaly, (2) determining the structural geometry from the gradient space plot, and (3) locating profile positions of structural corners from the vertical gradient profile. This generalized inversion procedure requires no quantitative information or assumption regarding density contrasts. Iterative forward modeling then predicts the density contrasts. Application of this generalized gravity gradient inversion procedure to high quality gravity data results in an effective density prediction consistent with measured near‐surface densities and the known increase in density with depth in deep sedimentary basins.

Download Full-text

VARIATIONS OF VERTICAL GRAVITY GRADIENT IN NEW YORK CITY AND ALPINE, NEW JERSEY

Geophysics ◽

10.1190/1.1440009 ◽

1969 ◽

Vol 34 (2) ◽

pp. 235-248 ◽

Cited By ~ 7

Author(s):

John T. Kuo ◽

Mario Ottaviani ◽

Shri K. Singh

Keyword(s):

New York ◽

New York City ◽

New Jersey ◽

York City ◽

Gravity Data ◽

Tall Buildings ◽

Base Station ◽

Absolute Gravity ◽

Gravity Gradient ◽

Vertical Gravity Gradient

Careful gravity measurements with La Coste‐Romberg geodetic gravimeters were carried out in tall buildings on a floor‐to‐floor basis in New York City and on the Armstrong Tower, Alpine, New Jersey. Corrections for the instrumental drift and tidal gravity variation and for the Bouguer effect, topography, mass of the buildings, and subway and basement excavations have been applied to the gravity data, which are tied to the absolute gravity value of the National Gravity Base Station of Washington, D. C. The observed gravity versus elevation curves are nonlinear, particularly near the surface of the ground; the slope of the observed gravity anomaly versus elevation curves reverses sign at an elevation of about 170 ft for the campus buildings and about 350 ft for the downtown buildings, and is nearly linear without a reversal for the Armstrong Tower. The vertical gradients vary substantially even within short distances. Comparisons of the corrected observed gradients with the theoretical gradients of gravity are made. The anomalous gradient anomalies are positive and are correlated with the positive isostatic surface gravity anomalies. Calibration of gravimeters against the observed vertical gradient of gravity to an accuracy of ±2 μgal is definitely feasible provided the gradient is predetermined to a comparable accuracy by a standard instrument.

Download Full-text

A new look at Belgian aeromagnetic and gravity data through image-based display and integrated modelling techniques

Geological Magazine ◽

10.1017/s0016756800020884 ◽

1993 ◽

Vol 130 (5) ◽

pp. 583-591 ◽

Cited By ~ 22

Author(s):

B. C. Chacksfield ◽

W. De Vos ◽

L. D'Hooge ◽

M. Dusar ◽

M. K. Lee ◽

...

Keyword(s):

Large Scale ◽

Gravity Data ◽

Bouguer Anomaly ◽

Digital Processing ◽

Integrated Modelling ◽

Magnetic Data ◽

Gravity Gradient ◽

The North ◽

Anomaly Map ◽

Shaded Relief

AbstractDigital processing and image-based display techniques have been used to generate contour and shaded-relief maps of Belgian aeromagnetic data at a scale of 1:300000 for the whole of Belgium. These highlight the important anomalies and structural trends, particularly over the Brabant Massif. North and vertically illuminated shaded-relief plots, enhanced structural belts trending west–east to northwest–southeast in the Brabant Massif and west–east to southwest–northeast in the core of the Ardennes. The principal magnetic lineaments have been identified from the shaded-relief plots and tentatively correlated to basement structures. Most short lineaments are correlated with individual folds while the more extensive lineaments are correlated with large scale fault structures. Magnetic highs within the Brabant Massif are attributed to folded sediments of the Tubize Group. The magnetic basement in the east of Belgium is sinistrally displaced to the north by an inferred deep NNW–SSE crustal fracture. The Bouguer anomaly map of Belgium identifies the Ardennes as a negative area, and the Brabant Massif as a positive area, with the exception of a WNW–trending gravity low in its western part. The southern margin of the Brabant Massif is defined by a steep gravity gradient coincident with the Faille Bordiere (Border Fault). Trial modelling of the gravity and magnetic data, carried out along profiles across the Brabant and Stavelot massifs, has identified probable acid igneous intrusions in the western part of the Brabant Massif, and a deep magnetic lower density body underlying the whole Ardennes region, which is thought to be a distinctive Precambrian crustal block.

Download Full-text

The structural/stratigraphic development of the Sishen South (Welgevonden) iron ore deposit, South Africa, as deduced from ground gravity data modelling

Applied Earth Science ◽

10.1179/174327506x138940 ◽

2006 ◽

Vol 115 (4) ◽

pp. 174-186

Author(s):

D. J. Alchin ◽

W. J. Botha

Keyword(s):

South Africa ◽

Iron Ore ◽

Gravity Data ◽

Data Modelling ◽

Ore Deposit ◽

Iron Ore Deposit

Download Full-text

SIMULATION MODELLING IN THE STRUCTURAL GRAVITY PROSPECTING

Prospecting and Development of Oil and Gas Fields ◽

10.31471/1993-9973-2019-2(71)-38-48 ◽

2019 ◽

pp. 38-48

Author(s):

S. H. Anikeyev ◽

S. M. Bahriy ◽

B. B. Hablovskiy

Keyword(s):

Cross Sections ◽

Gravity Data ◽

A Priori ◽

Structural Type ◽

Simulation Modelling ◽

Gravity Modeling ◽

Gravity Inversion ◽

Density Structure ◽

Data Modelling ◽

Computer Technologies

In accordance with the purpose of geophysical exploration, the gravity data interpretation is aimed at prospecting mineral resources which is based on the study of the geological cross-section structure. The task of quantitative interpretation, which uses methods of gravity modeling and gravity inversion, is the modelling of a gravity field (gravity modeling) and of a density structure of geological environments (gravity inversion). The article presents the definition and steps of the gravity data modelling technique. This technique is based on the construction of an informal sequence of equivalent solutions. The technological and geological features of methods for modelling the density structure of complex geological environments are given; among them geological content, consistency with a priori data and the subordination of modelling to geological hypotheses are important. The topicality and methods of simulation modelling are outlined. The purpose of simulation modelling is to study the properties of gravity inversion in the general formulation, as well as to evaluate the degree of detail and reliability of the methods and technologies of gravity modelling, which claim to be an effective solution to geological problems. The example of structural simulation testing of the methods of informal sequence of equivalent solutions and its computer technologies shows that a complex interpretation of seismic and gravity measurements data enables the creation of detailed density models of structural cross-sections. The ways of increasing the veracity of gravity data modelling of structural cross-sections have been studied. It is revealed that the best approximation of the regional background is an inclined plane which approximates the observed field of gravity according to characteristic pickets over the research areas that are better studied. The increase in the veracity of modeling can also be achieved by rebuilding the near side zones in the structural type models in an interactive process of solving structural gravity inversion problems. Substantive modeling depends primarily on the experience of the interpreter since computer technologies for gravity modeling and gravity inversion are merely an interpretation tool.

Download Full-text

Exploiting Aeromagnetic and Gravity Data Interpretation to Delineate Massif Deposits of Rehamna Area (Western Meseta-Morocco)

Iraqi Geological Journal ◽

10.46717/igj.54.2c.2ms-2021-09-21 ◽

2021 ◽

Vol 54 (2C) ◽

pp. 13-28

Author(s):

Kawtar Benyas

Keyword(s):

Gravity Data ◽

Precious Metals ◽

Data Interpretation ◽

Structural Features ◽

Magnetic Data ◽

Gravity Gradient ◽

Horizontal Gradient ◽

Geological Structures ◽

Magnetic Signatures ◽

First Vertical Derivative

The analysis of the magnetic signatures and gravity gradient values of the Rehamna Massif south of the Moroccan Western Meseta by using Geosoft Oasis Montaj 7.0.1 software, allowed us to detect several useful anomalies to be exploited and which are related to magmatic bodies and structural features within the study area. These data were analyzed by applying several techniques, including the horizontal gradient filters combined with the first vertical derivative. Subsurface structures; such as geological boundaries, faults, dykes and folds, were visualized as lineaments on geophysical maps, then results were compared with structural features provided by previous studies in the region. Thus, the Rehamna Massif structural map shows sets of linear features which may represent faults or boundaries of geological structures, which can be either faults or boundaries of geological structures, and they are mostly oriented in the directions: N-S, NNE-SSW, NE-SW, E-W with the predominance of the NNE-SSW to NE-SW directions. In addition, the super position of the minerals bearing beds or formations were distinguished from gravity and magnetic data processing results. Some of the recognized anomalies are related to the existence of precious metals which belong to the granitic bodies within the study area.

Download Full-text