Interactive modeling and interpretation of three dimensional gravity data

1982 ◽  
Author(s):  
H.‐J. Goetze ◽  
F. Keller ◽  
B. Lahmeyer ◽  
O. Rosenbach
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Interactive Modeling ◽  
Dimensional Gravity

Gravity ideal bodies

Geophysics ◽  
1987 ◽  
Vol 52 (9) ◽  
pp. 1265-1278 ◽  
Author(s):  
Mark E. Ander ◽  
Stephen P. Huestis
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Computer Code ◽  
Solution Set ◽  
Rio Grande Rift ◽  
Positive Anomaly ◽  
Dimensional Gravity ◽  
Exploration Tool ◽  
Ideal Body ◽  
Rigorous Bounds

The interpretation of gravity anomaly data suffers from a fundamental nonuniqueness, even when the solution set is bounded by physical or geologic constraints. Therefore, constructing a single solution that fits or approximately fits the data is of limited value. Consequently, much effort has been applied in recent years to developing inverse techniques for rigorous deduction of properties common to all possible solutions. To this end, Parker developed the theory of an ideal body, which characterizes the extremal solution with the smallest possible maximum density. Gravity ideal‐body analysis is an excellent reconaissance exploration tool because it is especially well suited for handling sparse data contaminated with noise, for finding useful, rigorous bounds on the infinite solution set, and for predicting accurately what data need to be collected in order to tighten those bounds. We present a practical three‐ dimensional gravity ideal‐body computer code, IDB, that can optimize a mesh with over [Formula: see text] cells when used on a CRAY computer. Using actual gravity data, we use IDB to produce ideal‐body tradeoff curves that bound the solution set and show how to restrict the bound on the solution further by applying geologic and geophysical data to the tradeoff curves. As an example, we compare two‐dimensional and three‐dimensional ideal‐body results from a study of a positive anomaly associated with the Lucero uplift located on the western flank of the Rio Grande rift in New Mexico.

Three-dimensional gravity modelling applied to the exploration of uranium unconformity-related basement-hosted deposits: the Contact prospect case study, Kiggavik, northeast Thelon region (Nunavut, Canada)

2017 ◽  
Vol 54 (8) ◽  
pp. 869-882 ◽  
Author(s):  
Régis Roy ◽  
Antonio Benedicto ◽  
Alexis Grare ◽  
Mickaël Béhaegel ◽  
Yoann Richard ◽  
...  
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Gravity Anomalies ◽  
3D Models ◽  
Low Density ◽  
Uranium Deposits ◽  
Geological Interpretation ◽  
Thelon Basin ◽  
Dimensional Gravity ◽  
Density Values

In unconformity-related uranium deposits, mineralization is associated with hydrothermal clay-rich alteration haloes that decrease the density of the host rock. In the Kiggavik uranium project, located in the eastern Thelon Basin, Nunavut (Canada), basement-hosted shallow deposits were discovered by drilling geophysical anomalies in the 1970s. In 2014, gravity data were inverted for the first time using the Geosoft VOXI Earth ModellingTM system to generate three-dimensional (3D) models to assist exploration in the Contact prospect, the most recent discovery at Kiggavik. A 3D unconstrained inversion model was calculated before drilling, and a model constrained by petrophysical data was computed after drilling. The unconstrained inversion provided a first approximation of the geometry and depth of a low-density body and helped to collar the discovery holes of the Contact mineralization. The constrained inversion was computed using density values measured on 315 core samples collected from 21 drill holes completed between 2014 and 2015. The constrained modelling highlights three shallower and smaller low-density bodies that match the geological interpretation and refines the footprint of the gravity anomalies in relation to the current understanding of the deposit. The 3D inversion of gravity data is a valuable tool to guide geologists in exploration of shallow basement-hosted uranium deposits associated with alteration haloes and to assess the deposit gravity geometry.

Three‐dimensional gravity or magnetic constrained depth inversion with lateral and vertical variation of contrast

Geophysics ◽  
1990 ◽  
Vol 55 (3) ◽  
pp. 327-335 ◽  
Author(s):  
D. Chenot ◽  
N. Debeglia
Keyword(s):  
Gravity Data ◽  
Three Dimensional ◽  
Sediment Compaction ◽  
Inhomogeneous Density ◽  
Dimensional Gravity ◽  
Well Data ◽  
Starting Model ◽  
Basin Area ◽  
Local Depth

Depth‐mapping inversion of gravity or magnetic fields generally assumes that anomalies originate from a main density or magnetization contrast interface. This particular inversion takes into account inhomogeneous density or magnetization distributions reflecting sediment compaction and basement heterogeneities: above the interface, the density can be approximated by an exponential function, and below it, an intrabasement contrast map can be used. The inversion also integrates local depth constraints from wells or seismic data, as well as general constraints set on the geometry and the contrast of the interface. After field transformations, spectral analysis and constraints help to define a starting model characterized mainly by the interface mean depth and the mean parameter contrast between the two media. The depth adjustment is completed iteratively under constraints using a space‐domain formulation derived from the Bouguer‐slab approximation. The interface model effect is computed in the wavenumber domain. A model data example shows the accuracy of the inversion and illustrates the role of the constraints. In a field example of a basin area where constraints can be derived from numerous well data, successive inversions of gravity data result in an isodepth map of the basement. The compatibility of the map with local depth constraints from wells is obtained by taking into account density heterogeneities related to known lithologic variations in the basement.

Crustal structure at the Trans-European Suture Zone in northwest Poland based on gravity data

1997 ◽  
Vol 134 (5) ◽  
pp. 661-667 ◽  
Author(s):  
C. KRÓLIKOWSKI ◽  
Z. PETECKI
Keyword(s):  
Crustal Structure ◽  
Gravity Data ◽  
Sedimentary Cover ◽  
Bouguer Anomaly ◽  
Three Dimensional ◽  
Suture Zone ◽  
Long Wavelength ◽  
Dimensional Gravity ◽  
Anomaly Map ◽  
Northwestern Poland

A new gravity model of the crustal structure of the Trans-European Suture Zone in the northwestern Poland has been constructed. The Bouguer anomaly map, obtained after stripping off the three-dimensional gravity effect of the sedimentary cover down to the Zechstein formations, is characterized by a 50 mGal gravity anomaly. We have assumed that the short-wavelength components derive from upper crustal intrusions and the long-wavelength components reflect crustal thickness and lateral heterogeneity which are strongly supported by the new seismic data along the LT-7 geotraverse. Quantitative modelling of gravity data along three profiles crossing the area indicate the presence of anomalous masses within the Lower Palaeozoic sequence, mainly along the Teisseyre-Tornquist Zone. Two of the profiles crossing the long-wavelength ‘stripped’ gravity high suggest the existence of a zone of 35 km crust above a dense upper mantle along the Teisseyre-Tornquist Zone. The extent of the zone can be determined based on the Bouguer anomalies interpretation.

scholarly journals Horizontal Gravity in Ocean Ekman transport

2021 ◽  
Author(s):  
Peter C. Chu
Keyword(s):  
Gravity Data ◽  
Surface Wind ◽  
Three Dimensional ◽  
Ocean Dynamics ◽  
Ekman Transport ◽  
Buoyancy Frequency ◽  
Data Set ◽  
Surface Wind Stress ◽  
Dimensional Gravity ◽  
New Formula

Abstract Three-dimensional gravity vector field g (= igλ+jgφ+kgz) in geodesy has been greatly simplified to a uniform vertical vector (-g0k) in oceanography with (λ, φ, z) the (longitude, latitude, height), (i, j, k) the corresponding unit vectors, and g0 = 9.81 m/s2. Recent studies by the author show such simplification incorrect. The horizontal gravity is important in ocean dynamics. Along the same path, the horizontal gravity is included into the classical Ekman layer dynamics with constant eddy viscosity and depth-dependent-only density ρ(z) represented by an e-folding near-inertial buoyancy frequency. A new Ekman spiral and in turn a new formula for the Ekman transport are obtained. With the horizontal gravity data from the global static gravity model EIGEN-6C4 and the surface wind stress data from the Comprehensive Ocean-Atmosphere Data Set (COADS), the Ekman transport due to the horizontal gravity is crucial and cannot be neglected.

Three-dimensional gravity analysis of the Kiglapait layered intrusion, Labrador

1979 ◽  
Vol 16 (1) ◽  
pp. 24-37 ◽  
Author(s):  
Randell Stephenson ◽  
Michael D. Thomas
Keyword(s):  
Gravity Anomaly ◽  
Gravity Data ◽  
Three Dimensional ◽  
Layered Intrusion ◽  
Southeastern Part ◽  
Model Studies ◽  
Maximum Thickness ◽  
Granitic Intrusion ◽  
Dimensional Gravity ◽  
Southeastern Region

The Kiglapait basic layered intrusion in northern Labrador previously has been interpreted, on geological grounds, to be a lopolith with a maximum thickness of 8.7 km. It is associated with a large (~45 mGal) positive gravity anomaly that for the most part is very similar to a theoretical anomaly computed for the proposed lopolith model, except over the southeastern part of the exposure where the theoretical anomaly is significantly more positive. Model studies of the gravity data suggest that the form and dimensions of the lopolithic model predicted on geological criteria are essentially valid and that a granitic intrusion is present in the southeastern region of the lopolith causing the discrepancy between observed and theoretical anomalies. The latter intrusion is believed to be genetically related to the Manvers granite, which occurs throughout the southeastern region as dykes and small stocks. The presence of another buried granitic mass south of the Kiglapait intrusion is also suggested by the gravity data.

Three-dimensional gravity inversion using graph theory to delineate the skeleton of homogeneous sources

Geophysics ◽  
2015 ◽  
Vol 80 (2) ◽  
pp. G53-G66 ◽  
Author(s):  
Rodrigo Bijani ◽  
Cosme F. Ponte-Neto ◽  
Dionisio U. Carlos ◽  
Fernando J. S. Silva Dias
Keyword(s):  
Genetic Algorithm ◽  
Graph Theory ◽  
Minimum Spanning Tree ◽  
Gravity Data ◽  
A Priori ◽  
Three Dimensional ◽  
Real Data ◽  
Gravity Inversion ◽  
Inversion Method ◽  
Dimensional Gravity

We developed a new strategy, based on graph theory concepts, to invert gravity data using an ensemble of simple point masses. Our method consisted of a genetic algorithm with elitism to generate a set of possible solutions. Each estimate was associated to a graph to solve the minimum spanning tree (MST) problem. To produce unique and stable estimates, we restricted the position of the point masses by minimizing the statistical variance of the distances of an MST jointly with the data-misfit function during the iterations of the genetic algorithm. Hence, the 3D spatial distribution of the point masses identified the skeleton of homogeneous gravity sources. In addition, our method also gave an estimation of the anomalous mass of the source. So, together with the anomalous mass, the skeleton could aid other 3D methods with promising geometric a priori parameters. Several tests with different values of regularizing parameter were made to bespeak this new regularizing strategy. The inversion results applied to noise-corrupted synthetic gravity data revealed that, regardless of promising starting models, the estimated distribution of point masses and the anomalous mass offered valuable information about the homogeneous sources in the subsurface. Tests on real data from a portion of Quadrilátero Ferrífero, Minas Gerais state, Brazil, were performed for complementary analysis of the proposed inversion method.

Sign in / Sign up

Export Citation Format

Share Document