Glossary¶

Quote

The only source of knowledge is experience.
― Albert Einstein

A¶

acceleration¶

The rate of change of velocity over time, often measured in meters per second squared (m/s $^2$ ). In geophysics, gravitational acceleration refers to the force exerted by gravity on objects at the Earth's surface.

API¶

API (Application Programming Interface): a set of protocols and tools for building software applications, allowing different software programs to communicate.

asthenosphere¶

A semi-fluid, ductile layer of the Earth's upper mantle located below the lithosphere. It is mechanically weaker than the overlying rigid lithosphere and allows for the movement of tectonic plates through slow convection. The asthenosphere plays a key role in plate tectonics, isostasy, and mantle convection, as its flow accommodates the motion of the plates and the distribution of heat from the Earth's interior.

B¶

basin¶

A low area in the Earth’s surface, often filled with sediments, studied for its potential as a resource reservoir.

Bessel Ellipsoid¶

The Bessel Ellipsoid, introduced in 1841 by Friedrich Bessel, is an early mathematical model of the Earth's shape based on arc measurements in Europe. It was widely used in European geodesy throughout the 19^th and early 20^th centuries. The Bessel Ellipsoid provided a more accurate regional fit for Europe compared to global models at the time.

body¶

In geophysics, a body refers to a distinct geological or physical entity within the Earth's subsurface, characterized by specific properties such as density, magnetic susceptibility, etc. Bodies can represent various geological formations, such as rocks, minerals, or fluids, and are often used in numerical models to simulate and analyze geophysical data.
In IGMAS+, a body is a 3D object with a defined shape and properties, composed of a set of triangles that form its convex hull.

Bouguer anomaly¶

A gravity anomaly that has been corrected for terrain and elevation, used to study subsurface mass distribution. The anomaly is named after Pierre Bouguer (1698–1758), a French mathematician, geophysicist, geodesist, and astronomer.

Bouguer correction¶

The adjustment to a measurement of gravitational acceleration to account for elevation and the density of rock between the measurement station and a reference level. It can be expressed mathematically as the product of the density of the rock, the height relative to sea level or another reference, and a constant, in units of mGal:

$\delta g_B = 2\pi G \rho h \approx 4.19358\cdot10^{−5}\cdot\rho h,$

where

$\delta g_B$ - Bouguer correction in mGal
$\rho$ - rock density in kg/m $^3$
$h$ - height difference between two locations in m, also called Bouguer plate thickness
$G$ - gravitational constant.

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bulk density¶

The overall density of a material, including both solid particles and the pore spaces between them. In subsurface geology, bulk density is important for determining rock and sediment composition and is often measured in subsurface modelling.

C¶

CAD (Computer-Aided Design)¶

CAD refers to software used to create precision drawings and 3D models. In geophysics and geology, CAD tools help design equipment, geological models, and infrastructure layouts, aiding in the visualization and planning of field operations and simulations.

central meridian¶

The central meridian is the longitudinal line at the center of a map projection zone, serving as the axis of least distortion. It is crucial in coordinate systems like the Universal Transverse Mercator (UTM) and other cylindrical projections. The central meridian helps minimize distortion near the middle of the projection zone, with distortion increasing as you move away from it.

CODATA¶

CODATA is the Committee on Data of the International Science Council (ISC) founded in 1966 (at that time known as the Committee on Data for Science and Technology). CODATA's mission is to connect data and people to advance science and improve our world by promoting international collaboration to advance Open Science and to improve the availability and usability of data for all areas of research.

The purpose of the CODATA Task Group on Fundamental Constants (CODATA-TGFC) is to periodically provide the scientific and technological communities with a self-consistent set of internationally recommended values of the fundamental physical constants, such as gravitational constant and conversion factors of physics and chemistry based on all of the relevant data available at a given point in time.

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Complete Bouguer Anomaly¶

Complete Bouguer Anomaly (CBA): a gravity anomaly that has been fully corrected for both elevation and the gravitational effect of terrain, building upon the Bouguer Anomaly. In addition to the standard Bouguer correction, which accounts for the gravitational influence of a flat slab of material between the measurement point and sea level, the Complete Bouguer Anomaly includes terrain corrections to remove the effects of local topography. This results in a more refined representation of subsurface mass distribution, making it especially useful in mountainous or rugged areas where topographic variations significantly affect gravity measurements. Like the Bouguer anomaly, it is expressed in mGal and is an important tool in geophysical exploration for identifying geological structures beneath the Earth's surface.

convex hull¶

Convex hull, or just hull, is the smallest convex shape that encloses a set of points, often used in spatial data processing and modelling.

core¶

The innermost layer of the Earth, consisting of two parts: the solid inner core and the liquid outer core. The core is primarily composed of iron and nickel and is responsible for generating Earth's magnetic field through the movement of molten metal in the outer core. The core plays a crucial role in Earth's geodynamics, including heat transfer and magnetic field generation.

covariance¶

Covariance is a measure of how two variables change together. If the variables tend to increase or decrease together, the covariance is positive; if one tends to increase while the other decreases, the covariance is negative. In geophysics, covariance is used to assess the relationships between different parameters, which is critical in uncertainty analysis and model fitting processes like inversion or parameter estimation.

The covariance between two variables $X$ and $Y$ , $Cov(X, Y)$ , can be calculated by taking the expected value, or mean, $E$ of the product of two values: the deviation of $X$ from its mean $\mu X$ and the deviation of $Y$ from its mean $\mu Y$ . That is:

$Cov(X, Y) = E[(X − \mu X)(Y − \mu Y)].$

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covariance matrix¶

A covariance matrix is a square matrix that represents the covariance between pairs of variables. Each element of the matrix indicates how much two variables change together. In geophysics, a covariance matrix can be used to quantify the relationships between different parameters in a model, helping in the uncertainty analysis or parameter optimization processes in techniques like potential field inversion.

Covariance Matrix Adaptation Evolution Strategy¶

Covariance Matrix Adaptation Evolution Strategy (CMA-ES) is an advanced optimization algorithm based on Evolution Strategy often used for solving non-linear problems. It evolves a population of candidate solutions and adapts their distribution by updating a covariance matrix, which allows the algorithm to effectively search the solution space. In geophysical studies, such as potential field modelling or inversion, CMA-ES can be applied to optimize model parameters by minimizing the misfit between observed and predicted data.

CPU (Central Processing Unit)¶

The CPU is the primary component of a computer that executes instructions from software, handling general-purpose tasks. While versatile, CPUs are less efficient for parallel processing compared to GPUs.

CRS (Coordinate Reference System)¶

A Coordinate Reference System (CRS) defines how spatial data is mapped to the Earth's surface. It includes parameters like datum, projection, and coordinate units, ensuring that geographic data aligns correctly across different datasets and software. CRS is essential in GIS, geophysics, and geodesy for accurate mapping and spatial analysis.

crust¶

The outermost layer of the Earth, consisting of solid rock. It is divided into oceanic and continental crust and varies in thickness, playing a key role in geophysical studies of gravity and magnetics.

D¶

data visualization¶

The graphical representation of data to help users understand trends, patterns, and insights, often used in subsurface modelling.

datum¶

A datum is a reference framework for measuring locations on the Earth's surface. It defines the origin and orientation of a coordinate system, often based on an ellipsoid that approximates the Earth's shape. Datums are crucial in geodesy and GIS for accurate mapping and positioning.

DEM¶

DEM (Digital Elevation Model): a 3D representation of a terrain's surface created from terrain elevation data. It is commonly used in geographic information systems (GIS), remote sensing, and various engineering applications to model landscapes and analyze topography.

density¶

A physical property of matter defined as mass per unit volume, often measured in kilograms per cubic meter (kg/m $^3$ ). In geophysics, density variations in the Earth's materials can influence gravity and magnetic fields.

DTD (Document Type Definition)¶

DTD is a set of rules that defines the structure and legal elements and attributes of an XML document. It ensures that XML data adheres to a specific format by validating the document’s elements, nesting, and data types. DTDs are essential in data exchange, web development, and geophysical applications where consistent data formats are crucial for interoperability and model configuration.

E¶

earthquake¶

The sudden release of energy caused by the shifting of tectonic plates, volcanic activity, or other reasons, resulting in ground shaking. Earthquakes are a key focus in geophysics and seismology and provide insights into subsurface structures and geodynamics.

Evolution Strategy¶

Evolution Strategy (ES) is an optimization technique inspired by the process of natural selection. It is commonly used in fields like machine learning and numerical modelling to solve complex optimization problems. In geophysics, ES can be applied to potential field modelling, helping to iteratively improve solutions to fit observed gravity or magnetic data. Unlike genetic algorithms, ES focuses more on the evolution of continuous parameters rather than discrete gene-like structures, making it suitable for refining models in scientific computing.

ENU system¶

The ENU system is a local geodetic coordinate system used in geophysics and navigation, where coordinates are defined relative to a specific point on the Earth's surface. The three axes are:

East (E): Positive towards the east.
North (N): Positive towards the north.
Up (U): Positive vertically, away from the Earth's center.

This system is essential for mapping, GPS positioning, and representing vector data.

EPSG (European Petroleum Survey Group)¶

EPSG is a standard for coordinate reference systems and spatial data projections, widely used in geodesy, GIS, and mapping. The EPSG database assigns unique codes to coordinate systems, datums, and projections, ensuring consistency in geospatial data processing and exchange.

expected value¶

Expected value is the average or mean value that one would expect from a random variable over many trials. It represents the central tendency of a probability distribution. In geophysics, the expected value is often used in probabilistic models or uncertainty analysis to predict the most likely outcome of a parameter based on known data or distributions.

Mathematically,

$E(X) = \sum_{i=1}^{n} x_i \cdot P(x_i),$

where:

$E(X)$ is the expected value,
$x_i$ represents each possible value of the random variable $X$ ,
$P(x_i)$ is the probability of $x_i$ ,
$n$ is the total number of possible outcomes.

F¶

fault¶

A fracture or zone of fractures in the Earth's crust along which there has been displacement of the rock on either side. Faults are caused by tectonic forces and are often associated with earthquakes, as stress builds up and is released along these fractures. Faults can be classified into different types, such as normal, reverse, and strike-slip, depending on the direction of movement.

flying carpet¶

Flying carpet is a term used in geophysics to describe a method of visualizing and interpreting geophysical data. It involves creating a 3D representation of the subsurface, where the data is "floated" above the ground surface, allowing for better visualization of geological structures and anomalies. In the context of IGMAS+, the flying carpet is often used to describe the interface between different geological layers or the topography of the subsurface, or horizons.

fold¶

A fold is a geological structure formed by the bending or warping of rock layers due to tectonic forces. Folds can vary in size and shape, and they are classified into different types, such as anticlines (upward folds) and synclines (downward folds). Folds are important in geology and geophysics as they can indicate the presence of oil and gas reservoirs, mineral deposits, and other geological features.

forward modelling¶

A method of predicting how a physical system behaves by applying known physical laws to create a model of the system.

forward problem¶

In geophysics, a forward problem involves predicting the observable data (such as gravity, magnetic fields, or seismic waves) based on a known model of the subsurface, including properties like density, magnetic susceptibility. It is the opposite of an inverse problem, where the goal is to infer the subsurface properties from observed data. Forward modelling helps validate assumptions and simulate how geological structures will affect geophysical measurements.

free-air correction¶

A correction applied to gravity measurements to account for changes in elevation above sea level. It adjusts the measured gravity value to what it would be at a standard elevation, assuming no mass between the observation point and sea level. This correction is used to isolate the effect of elevation from other gravitational influences.

free-air gravity anomaly¶

The measured gravity anomaly after a free-air correction is applied to account for the elevation at which a measurement is made.

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G¶

gal¶

Unit of acceleration, named in honour of the Italian physicist and astronomer Galileo Galilei (1564–1642) and used especially in measurements of gravity. One gal (Gal) equals a change in rate of motion of 1 cm per second per second (0.01 m/s $^2$ ). The milligal (mGal) and microgal ( $\mu$ Gal) are respectively one thousandth and one millionth of a Gal.

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Gauss-Krueger Coordinate System¶

The Gauss-Krueger (Gauß-Krüger) system is a transverse cylindrical map projection used primarily in Europe and Asia for large-scale mapping and geodetic surveys. It is similar to the UTM (Universal Transverse Mercator) system but differs in zone width and reference conventions.

Gaussian Quadrature¶

Gaussian Quadrature is a numerical integration technique used to approximate the integral of a function, particularly in potential field modelling and geophysical data analysis. It achieves high accuracy by selecting optimal points (nodes) and weights, reducing computational effort compared to standard methods like the trapezoidal rule. This method is essential in solving complex integrals arising in gravity and magnetic modelling.

Genetic Algorithm¶

Genetic Algorithm (GA) is a heuristic optimization technique inspired by the process of natural selection. It uses operations like selection, crossover, and mutation to evolve solutions toward optimal results. In geophysical modelling, GAs can be applied to fit observed gravity and magnetic data by evolving potential field models over successive generations to minimize error or improve accuracy.

geodesy¶

Geodesy is the science of measuring and understanding the Earth's shape, orientation in space, and gravitational field. It provides the foundation for mapping, navigation, and geophysical studies by establishing accurate coordinate systems and reference frames. Geodesy is essential for GPS, surveying, and monitoring Earth's dynamic processes, such as plate tectonics and sea level changes.

geodynamics¶

The study of the forces and processes that drive the movement and deformation of the Earth's crust, mantle, and core. It encompasses plate tectonics, mantle convection, earthquakes, volcanic activity, and the flow of heat and materials within the Earth. Geodynamics helps explain the Earth's changing structure and the physical mechanisms behind gravity, magnetism, and tectonic movements.

geoid¶

The hypothetical shape of the Earth, representing mean sea level, used as a reference for gravity measurements.

geology¶

The science of the Earth's physical structure, composition, and history. It focuses on studying rocks, minerals, and geological processes like tectonics, erosion, and sedimentation, helping to understand the Earth’s past and predict future changes.

geomagnetic field¶

The magnetic field surrounding the Earth, generated by movements in its molten outer core.

geometry optimization¶

In subsurface modelling, geometry optimization is the process of refining the shapes, positions, and boundaries of subsurface structures (such as bodies, layers, layer boundaries, faults) to achieve the best fit with geophysical data, such as gravity, magnetic, or seismic measurements.

geophysical inversion¶

A process of using observed data to derive a model of the subsurface, e.g. for gravity or magnetic fields.

geophysics¶

The branch of earth sciences that uses physical methods, such as gravity, magnetics, and seismic waves, to study the Earth's structure, composition, and processes. Geophysics is essential for exploring subsurface features and resources and understanding geodynamic activities.

georeferencing¶

Georeferencing is the process of aligning spatial data to a known coordinate system so it can be accurately mapped. This involves assigning real-world coordinates (latitude/longitude or projected coordinates) to images, maps, or datasets. In geophysics, georeferencing is vital for overlaying survey data onto base maps and ensuring accurate positioning in GIS applications.

GIS (Geographic Information System)¶

A Geographic Information System (GIS) is a framework for gathering, managing, and analyzing spatial and geographic data. It integrates data layers with maps to visualize, interpret, and analyze relationships, patterns, and trends. GIS is essential in geophysics for mapping geological features, analyzing potential fields, and managing survey data.

Gouraud shading¶

An interpolation method used in computer graphics to produce continuous shading of surfaces represented by polygon meshes, named after Henri Gouraud.

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GPU (Graphics Processing Unit)¶

A GPU is a specialized processor designed to accelerate graphics rendering and parallel computations. GPUs excel at handling large datasets and complex simulations, making them essential for 3D geological modeling, seismic data processing, and potential field visualization.

gravimeter¶

An instrument used to measure the strength of gravitational fields at specific locations.

gravitational acceleration¶

The acceleration due to Earth's gravity at or near its surface, typically denoted as $g$ and approximately equal to 9.8 meters per second squared (m/s $^2$ ). It represents the force of gravity acting on objects and varies slightly with altitude and geographical location due to Earth's shape and mass distribution.

gravitational constant¶

A physical constant denoted by $G$ and used in calculating the gravitational attraction between two objects. In Newton's law of universal gravitation, the attractive force between two objects ( $F$ ) is equal to $G$ times the product of their masses ( $m_1 m_2$ ) divided by the square of the distance between them ( $r^2$ ):

$F = G \frac{m_1 m_2}{r^2}.$

The value of $G$ is (6.67430 ± 0.00015) ⋅ 10 $^{−11}$ m $^3$ kg $^{−1}$ s $^{−2}$ or (6.67430 ± 0.00015) ⋅ 10 $^{−6}$ mGal m $^2$ kg $^{−1}$ , as recommended in 2018 by the CODATA.

Note, that the default value of $G$ used in IGMAS+ is 6.67384 ⋅ 10 $^{−11}$ m $^3$ kg $^{−1}$ s $^{−2}$ , but users can change it, as explained here.

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gravity¶

A natural force of attraction between objects that have mass. On Earth, gravity pulls objects toward the planet's center, giving them weight. In geophysics, gravity is used to study variations in the Earth's subsurface by measuring changes in gravitational force, which can indicate differences in rock density and geological structures.

gravity anomaly¶

The difference between the observed value of gravity and the value predicted by a theoretical model at a location on the Earth's surface.

Different theoretical models will predict different values of gravity, and so a gravity anomaly is always specified with reference to a particular model. The Bouguer, free-air, and isostatic gravity anomalies are each based on different theoretical corrections to the value of gravity.

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gravity field¶

The region of space around a mass where the force of gravity is exerted. In geophysics, variations in the Earth's gravity field help map subsurface structures and densities.

gravity gradient¶

The rate of change of gravitational acceleration with distance. This measurement provides detailed information about subsurface mass distribution and is used to detect variations in rock density and other geological features.

GUI¶

GUI (Graphical User Interface): a visual interface that allows users to interact with computers or applications through graphical elements like buttons, icons, and menus, rather than typing text commands.

H¶

half-space¶

In geophysics, a half-space refers to a theoretical, homogeneous, and infinite subsurface region extending below a boundary, often used in mathematical models to simplify the study of gravitational, magnetic, or seismic responses. It is assumed to have uniform properties such as density or magnetization, and is useful for approximating real-world conditions in subsurface modelling.

Hayford Ellipsoid¶

The Hayford Ellipsoid, also known as the International Ellipsoid of 1924, is a mathematical model of the Earth's shape, representing it as an oblate spheroid. It was one of the first globally adopted reference ellipsoids for geodesy and mapping, providing a standard for international measurements. The Hayford Ellipsoid approximates the Earth's surface more accurately than earlier models, aiding in the development of coordinate systems and geophysical studies.

horizon¶

In geophysics and geology, a horizon refers to a distinct layer within the Earth's subsurface, often identified by contrasts in rock type, geophysical properties, or stratigraphy. Horizons are key markers in seismic and potential field data interpretation, aiding in structural and stratigraphic modelling.

HTML¶

HTML (Hypertext Markup Language): the standard markup language used to create and design web pages. It structures content on the web using elements like headings, paragraphs, links, and images.

hull¶

A hull typically refers to the convex hull, the outer boundary or envelope of a set of points in space, often used in 3D modelling and visualization. The hull can represent the limits of geological bodies, survey data, or other spatial datasets, helping to define the extent of a region of interest.

I¶

interface¶

In geophysics and geology, an interface refers to the boundary or surface between two different geological layers or materials, such as between rock and sediment or between different rock types. Interfaces are critical in interpreting geophysical data, as they often represent changes in physical properties like density, magnetic susceptibility, seismic velocity, which can indicate the presence of resources or geological structures.
In IGMAS+, an interface is a set of triangles separating two bodies.

interpolation¶

Interpolation is a mathematical method used to estimate unknown values within a range of known data points. In geophysics, interpolation is crucial for creating continuous models from discrete measurements, such as gravity or magnetic data. It helps visualize subsurface structures and properties by filling in gaps in the data.

inverse modelling¶

A technique used to estimate subsurface properties by adjusting a model until it matches observed data, such as gravity or magnetic anomalies.

inverse problem¶

In geophysics and other scientific fields, an inverse problem involves using observed data to infer the underlying physical properties or structures that produced the data. Unlike forward problems, where the outcome is predicted from known inputs, inverse problems aim to reconstruct subsurface models (such as density or magnetic susceptibility) from measurements like gravity, seismic, or magnetic data. Solving inverse problems is critical for understanding subsurface geology and resource exploration.

interpolation¶

Interpolation is a mathematical technique used to estimate values at unknown points by using known data points. In geophysics, interpolation is essential for creating continuous models from discrete measurements. It plays a key role in numerical modelling, image processing, and grid-based data visualization.

isostasy¶

The concept in geophysics that describes the gravitational equilibrium between the Earth's lithosphere (crust and upper mantle) and the denser, underlying asthenosphere. According to isostasy, the Earth's crust "floats" at an elevation that balances the downward gravitational force of its mass and the upward buoyant force exerted by the mantle. This concept explains why mountain ranges have deep "roots" of crustal material extending into the mantle, and why regions with thick, less dense crust rise higher than those with thin, denser crust. Isostasy is central to understanding large-scale geological processes like crustal deformation, tectonics, and the distribution of mass within the Earth.

isostatic correction¶

A correction applied to gravity data to account for isostatic equilibrium, which assumes that the Earth's crust is "floating" in gravitational balance over the denser mantle. This correction adjusts for the mass differences caused by variations in topography (such as mountain ranges or ocean basins) and compensates for the corresponding "roots" beneath these features. The goal is to isolate the gravity signal caused by subsurface structures rather than surface-level mass differences, often used in conjunction with Bouguer Anomaly studies to provide deeper insights into crustal density and composition.

isostatic gravity anomaly¶

A type of gravity anomaly that accounts for variations in the Earth's gravity field due to differences in the density and elevation of crustal rocks. It is corrected for isostatic equilibrium, meaning the Earth's crust is assumed to be "floating" in balance, compensating for the mass of mountains and valleys.

isosurface¶

An isosurface is a three-dimensional surface representing points of constant value within a scalar field, such as temperature, pressure, or density. In geophysics, isosurfaces are used to visualize subsurface structures in seismic data or other parameter distributions, aiding in the interpretation of geological formations. They are generated through algorithms like Marching Cubes.

J¶

JDK¶

JDK (Java Development Kit): a software development kit used to write, compile, and run Java programs. It includes the JRE as well as tools like the Java compiler and debugger.

JRE¶

JRE (Java Runtime Environment): a software package that provides the libraries, JVM, and other components needed to run Java applications.

JVM¶

JVM (Java Virtual Machine): A core component of the Java programming language that enables Java programs to run on any device or operating system. It interprets and executes compiled Java bytecode, providing platform independence by allowing the same code to run on different platforms.

K¶

KML (Keyhole Markup Language)¶

A KML file (Keyhole Markup Language) is an XML-based format used to store geographic data for visualization in mapping applications like Google Earth and GIS platforms. KML files can represent points, lines, polygons, and images, enabling users to overlay geospatial data on 3D earth models. In geophysics, KML files are often used to display survey paths, geophysical anomalies, and potential field data in a spatial context, facilitating better interpretation and presentation.

L¶

layer cake¶

A layer cake is a simplified model of the Earth's subsurface, where different geological layers are represented as distinct, horizontal strata. This model is often used in geophysical to describe vertical variations in properties like density or magnetic susceptibility assuming uniformity within each layer. The layer cake model helps in understanding the stratigraphy and structure of the subsurface, aiding in resource exploration and geological mapping.
The key assumption of the layer cake model is that each layer is homogeneous and is defined by its thickness and physical properties across the entire area of model. This simplification allows for easier analysis and interpretation of geophysical data, as well as it is easier for numerical modelling, but such a model may not accurately represent complex geological formations like salt domes, folds, or faults.

Lithosphere¶

The rigid outer layer of the Earth, including the crust and upper mantle, involved in tectonic and subsurface studies.

M¶

magnetic anomaly¶

Deviation from the Earth's expected magnetic field, revealing subsurface features like mineral deposits.

magnetic field¶

The region around a magnetic material or moving electric charge where magnetic forces are exerted. The Earth's magnetic field is generated by its core and provides data about the structure and composition of the subsurface.

magnetic gradient¶

The rate of change of the Earth's magnetic field strength over distance. It is used in geophysics to detect small-scale variations in magnetic properties and to map subsurface features such as mineral deposits.

magnetic susceptibility¶

Quantitative measure of the extent to which a material may be magnetized in relation to a given applied magnetic field. The magnetic susceptibility of a material, commonly symbolized by $\chi_m$ , is equal to the ratio of the magnetization $M$ within the material to the applied magnetic field strength $H$ , or $\chi_m = M/H$ . This ratio, strictly speaking, is the volume susceptibility, because magnetization essentially involves a certain measure of magnetism (dipole moment) per unit volume.

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magnetization¶

The degree to which a material, typically rocks, becomes magnetized in the presence of an external magnetic field. It reflects the alignment of magnetic minerals within the material and provides important insights into the Earth's past magnetic field, as well as the composition and structure of the subsurface.

magnetism¶

A physical phenomenon produced by the motion of electric charges, leading to the attraction or repulsion of objects. In geophysics, Earth's magnetism, generated by the core, is studied to understand the magnetic field and its interactions with subsurface materials, helping map geological structures.

magnetometer¶

A device that measures magnetic field intensity and variations in the Earth's magnetic field.

mantle¶

The layer of the Earth located between the crust and the core, extending to a depth of about 2,900 kilometers. It is composed mostly of silicate rocks rich in magnesium and iron and behaves as a solid but flows slowly over geological time. The mantle plays a key role in plate tectonics, volcanic activity, and the transfer of heat and materials within the Earth.

mantle convection¶

The slow, churning movement of the Earth's mantle. Hotter, less dense material rises while cooler, denser material sinks, driving plate tectonics and influencing volcanic activity, earthquakes, and the formation of geological features.

Marching Cubes¶

Marching Cubes is an algorithm used to extract a polygonal mesh of an isosurface from a three-dimensional scalar field (often a 3D grid of values). It is widely applied in geophysics for visualizing subsurface data, seismic interpretation, and medical imaging. The method calculates surface intersections within grid cells and constructs a triangulated representation of the surface. This algorithm is essential for rendering volumetric data in potential field modelling and numerical simulations.

mass density¶

The amount of mass per unit volume of a substance, synonymous with density. Mass density is a key parameter in understanding the distribution of materials in the Earth's crust and mantle.

mass point¶

A mass point is an idealized object representing a body with mass concentrated at a single point. In geophysics, mass points are used in potential field modelling to simplify gravitational or magnetic field calculations. They serve as sources in numerical simulations, helping to approximate the effects of complex geological structures.

model vertice¶

Model vertices are the points in a 3D model that define its shape and structure. In geophysical modelling, these vertices represent the corners of polygons or mesh elements used to create a visual representation of subsurface features. They are essential for rendering and analyzing geological structures in software applications.

Moho (Mohorovičić Discontinuity)¶

The Moho is the boundary between Earth's crust and the mantle, named after Andrija Mohorovičić, a Croatian seismologist who discovered it in 1909. It marks a distinct change in seismic wave velocities, reflecting the transition from less dense crustal rocks to denser mantle materials. The Moho plays a crucial role in understanding crustal thickness and geophysical surveys involving seismic, gravity, and magnetic data.

N¶

numerical modelling¶

Numerical modelling involves using mathematical models and computational techniques to simulate real-world physical processes. In geophysics, this method is essential for interpreting gravity, magnetic, and other geophysical data, e.g. by simulating density or seismic velocity models to understand subsurface structures.

O¶

OpenCL (Open Computing Language)¶

OpenCL is an open standard for parallel programming of heterogeneous systems, including CPUs and GPUs. It enables developers to accelerate computing tasks by distributing workloads across diverse processors, making it valuable for geophysical modeling, numerical simulations, and large-scale data processing in IT and scientific applications.

OpenGL (Open Graphics Library)¶

OpenGL is a cross-platform API for rendering 2D and 3D vector graphics. It is widely used in graphics-intensive applications such as geophysical visualization, CAD, and game development. OpenGL allows for efficient rendering of models and simulations, playing a key role in visualizing potential field data and geological formations.

optimization¶

Optimization refers to the process of finding the best solution from a set of possible solutions, often by maximizing or minimizing a particular function. In geophysics, optimization is crucial for tasks like refining models of Earth's subsurface based on seismic, gravity and magnetic data, where algorithms (like genetic algorithms or evolution strategies) help fine-tune parameters to achieve the most accurate representation of geological features.

P¶

potential field¶

A field, such as gravity or magnetics, where the force is a function of position and can be described by a potential function.

plate tectonics¶

A scientific theory that describes the large-scale movement of Earth's lithosphere, which is divided into tectonic plates.

polygon¶

A polygon is a two-dimensional geometric figure with straight sides. In geophysics, polygons are often used to represent geological features, survey areas, or boundaries in GIS applications. They can be defined by a series of vertices (points) connected by edges, forming a closed shape or hull.

polyhedron¶

A polyhedron is a three-dimensional geometric shape with flat polygonal faces, straight edges, and vertices. In IGMAS+ polyhedra are used to represent complex geological structures, such as bodies or horizons, in 3D models. They are essential for visualizing subsurface features and conducting numerical simulations in IGMAS+ and geophysical applications in general.

PROJ¶

PROJ (also knows as PROJ.4) is an open-source software library used for cartographic projections and coordinate transformations. It enables the conversion of geographic coordinates between different coordinate reference systems by applying mathematical models of the Earth's shape, such as ellipsoids and geoids.

projection¶

A projection transforms the Earth's curved surface into a flat, two-dimensional map. This process inevitably introduces distortions in area, shape, distance, or direction. Different projections are chosen based on the purpose of the map and the region being represented. In geophysics and GIS, projections are crucial for spatial analysis and accurate visualization.

Q¶

R¶

reference body¶

In IGMAS+, a reference body is a special body that surrounds all other bodies in a model.
The reference body is defined by the reference density.

reference density¶

Reference density is a baseline or assumed constant density value used in gravity and potential field modelling to calculate density contrasts in the subsurface. In IGMAS+ reference density is a density value of the reference body, therefore, the reference density is the density, which surrounds the entire model. The reference density is subtracted from the density values of each body when calculating of their gravity responses.

reference meridian¶

A reference meridian is the prime longitudinal line used as the starting point for measuring longitude. It serves as a global standard for geographic coordinate systems. The most widely recognized reference meridian is the Greenwich Prime Meridian (0° longitude), adopted internationally in 1884.

remanent magnetization¶

The magnetization retained by a rock after the removal of an external magnetic field, revealing past geomagnetic conditions.

S¶

salt dome¶

A salt dome is a geologic structure formed when a mass of salt (halite) moves upward through overlying sedimentary rock layers. This occurs due to salt's lower density compared to surrounding rocks, causing it to rise. Salt domes are significant in geophysics, particularly in gravity and seismic studies, because they can distort the Earth's potential fields and serve as traps for hydrocarbons, making them important in oil and gas exploration. Salt domes affect the propagation of seismic waves due to salt's unique physical properties (high velocity of seismic waves and low absorption), which often result in challenges when interpreting seismic data.

sediments¶

Particles of rock, minerals, or organic material that have been transported and deposited by wind, water, or ice. Over time, these can compact and lithify to form sedimentary rocks, often studied in subsurface geology.

seismic imaging¶

Seismic imaging is a geophysical technique used to create detailed pictures of the Earth's subsurface by analyzing the propagation of seismic waves. It involves recording seismic waves, typically generated by controlled sources or natural earthquakes, and processing the data to visualize geological structures. This method is widely used in oil and gas exploration, mineral prospecting, and understanding fault zones for earthquake studies.

seismic waves¶

Seismic waves are vibrations that travel through the Earth, typically caused by earthquakes, volcanic activity, or artificial explosions. They are categorized into two main types: body waves (P-waves and S-waves), which travel through the Earth's interior, and surface waves (Love and Rayleigh waves), which travel along the Earth's surface. Seismic waves are crucial in geophysical studies for investigating the Earth's internal structure and in seismic imaging for resource exploration.

seismicity¶

The frequency, distribution, and magnitude of earthquakes in a specific region over time. It provides valuable information about tectonic activity, fault movements, and stress accumulation in the Earth's crust. Seismicity is studied to understand earthquake patterns, assess hazards, and explore subsurface geological structures.

seismology¶

Seismology is the scientific study of earthquakes and the propagation of seismic waves through the Earth. It aims to understand the mechanisms of earthquakes, the behavior of seismic waves, and the Earth's internal structure. Seismology plays a crucial role in earthquake monitoring, hazard assessment, and resource exploration by analyzing seismic data to map subsurface structures.

slab¶

A portion of the Earth's lithosphere, often referring to a tectonic plate that has been subducted beneath another plate. Slabs influence gravity and magnetic fields and are key features in plate tectonics and subsurface studies.

spatial anti-aliasing¶

In digital signal processing, spatial anti-aliasing is a technique for minimizing the distortion artifacts (aliasing) when representing a high-resolution image at a lower resolution. Anti-aliasing is used in digital photography, computer graphics, digital audio, and many other applications.

Source

standard deviation¶

Standard deviation is a statistical measure that quantifies the amount of variation or dispersion of a set of values from its mean. A low standard deviation indicates that the values are close to the mean, while a high standard deviation indicates greater variability. In geophysics, it is used to assess the spread or uncertainty of model parameters or data measurements, providing insight into data reliability.

It is calculated using the formula:

$\sigma = \sqrt{ \frac{1}{N} \sum_{i=1}^{N} (x_i - \mu)^2},$

where:

$\sigma$ is the standard deviation,
$N$ is the number of data points,
$x_i$ is each individual data point,
$\mu$ is the mean of the data set.

stratigraphy¶

Stratigraphy refers both to the study of layered rock formations and the actual sequence of these layers in the subsurface. In geophysical applications, stratigraphy is interpreted from seismic, gravity, and magnetic data to identify horizons, model geological history, and support exploration and resource assessments.

stress¶

The force per unit area applied to a material, such as rock, that can cause deformation or fracturing. In geophysics, stress in the Earth's crust is caused by tectonic forces, leading to phenomena such as earthquakes and the formation of faults. There are three primary types of stress: compressional, tensional, and shear, each influencing how rocks deform or break.

subsurface modelling¶

The process of creating a representation of the Earth’s subsurface using geophysical data, such as seismic, gravity, magnetic data, to understand geological structures and material properties.

SVD¶

SVD (Singular Value Decomposition): a mathematical technique used in data analysis and modelling to decompose a matrix into three components: singular vectors and singular values. In geophysics, SVD is often applied to solve inverse problems, process potential field data, and enhance subsurface imaging by reducing noise and extracting key features from complex datasets.

T¶

tectonic plate¶

A massive slab of Earth's lithosphere that moves and interacts with other plates, influencing gravity and magnetic fields.

terrain correction¶

A correction applied to gravity measurements to account for the gravitational influence of surrounding topographic features such as hills, valleys, and mountains. This correction refines the Bouguer Anomaly by adjusting for the variations in gravitational pull caused by uneven terrain. It is particularly important in rugged or mountainous areas, where topography significantly affects gravity data, ensuring that subsurface interpretations are not distorted by surface features.

tidal correction¶

A correction applied to gravity measurements to account for the gravitational effects of tidal forces from the Moon and the Sun. These celestial bodies cause variations in Earth's gravity field as they exert their pull on the Earth, leading to slight fluctuations in measured gravity values. Tidal correction removes this time-varying influence, ensuring that gravity data reflects only the local geological conditions and not temporary effects from tides.

topography¶

The physical shape and features of the Earth's surface, including mountains, valleys, plains, and other landforms. In geophysics, topography influences gravity and magnetic data, as variations in elevation and surface features affect measurements. Correcting for topographic effects (through methods like terrain correction) is crucial for accurately interpreting subsurface structures in gravity and magnetic surveys.

topology¶

Topology is a branch of mathematics that studies the properties of space that are preserved under continuous transformations. Model topology refers to the arrangement and connectivity of elements within a model. In IGMAS+ we understand by topology of a model the relationships between its elements, such as bodies, interfaces, and horizons. It is used to define how these elements are connected or interact with each other, which is essential for understanding the overall structure and behavior of the model.

triangulation¶

Triangulation is the process of dividing a geometric surface or space into triangles, which can be used to approximate shapes and surfaces. In geophysics, triangulation is critical for creating 3D models of geological structures, isosurfaces, and topographic maps. This technique enhances numerical modelling, interpolation, and visualization by breaking complex surfaces into simpler elements.

U¶

uncertainty¶

Uncertainty refers to the lack of certainty in measurements, predictions, or model outcomes. In geophysics, uncertainty can arise from limitations in data quality, measurement errors, or assumptions made during modelling. Understanding and quantifying uncertainty is essential for interpreting geophysical models and assessing the reliability of conclusions, particularly in processes like inversion and potential field studies.

uncertainty analysis¶

Uncertainty analysis involves quantifying the degree of uncertainty in model parameters or predictions. In geophysics, it is crucial to assess how uncertainties in data, model assumptions, or input parameters can affect the reliability of the results. This helps in determining the confidence in models, such as those derived from potential field inversion, and understanding the range of possible solutions for a given dataset.

UTM (Universal Transverse Mercator)¶

The Universal Transverse Mercator (UTM) is a global coordinate system that divides the Earth into 60 longitudinal zones, each spanning 6 degrees. It uses a transverse Mercator projection to map curved surfaces onto a flat grid with minimal distortion. UTM coordinates are widely used in geophysics, surveying, and GIS for precise location mapping and spatial analysis.

V¶

variance¶

Variance is a statistical measure that describes the extent to which a set of values deviates from its mean. In geophysical studies, variance can be used to quantify the variability or spread of parameters, helping to assess data reliability or model stability. Higher variance indicates greater variability in the data or parameters being analyzed.

Mathematically it is the square of the standard deviation.

vertex¶

Vertices are the points in a geometric shape where edges meet. In 3D models, vertices define the corners of polygons or mesh elements, forming the structure of the model. Vertices are used to represent geological features, survey data, and other spatial information in visualizations and numerical simulations.
In IGMAS+, vertices are used to define the model geometry at working sections, including the shape and position of geological bodies and interfaces.

volcanic activity¶

The eruption of molten rock (magma), ash, and gases from a volcano. It is driven by mantle convection and plate tectonics, and it plays a significant role in shaping the Earth's surface, contributing to crust formation and geophysical phenomena like gravity and magnetic anomalies.

voxel¶

A voxel, short for "volumetric pixel," is a three-dimensional pixel element used to represent a value on a regular grid in three-dimensional space. Similar to how a pixel represents a point or an area in a two-dimensional image, a voxel represents a point or a volume element in a three-dimensional space, typically in the context of computer graphics, medical imaging and scientific visualization. Each voxel contains information about properties such as color, density, texture, or other attributes, depending on the application. Voxel-based representations are commonly used in various fields for tasks like modelling, simulation, analysis, and rendering of three-dimensional data.

In IGMAS+, voxels are used to encounter parameter variations (density/susceptibility).

voxel cube¶

In IGMAS+, a voxel cube is a volume consisting of many sub-volumes, or voxels. The term "cube" is not a correct term here, parallelepiped is the appropriate one. The term "cube" is used for historical reasons and simplicity.

W¶

WGS84 (World Geodetic System 1984)¶

WGS84 is the global standard coordinate system and datum used for GPS. It models the Earth as an ellipsoid and provides a common reference frame for geospatial data worldwide. WGS84 defines the shape of the Earth and serves as the basis for most modern mapping, navigation, and geophysical applications.

WKT (Well-Known Text)¶

WKT (Well-Known Text) is a text-based format used to describe geospatial data and coordinate reference systems. It provides a human-readable way to represent geometric shapes (like points, lines, and polygons) and coordinate systems used in GIS.

working section¶

Working section in IGMAS+ is a vertical user-defined plane used for constructing and editing the 3D density model.
All model vertices lie on these parallel planes, which serve as interactive canvases for defining interfaces and geological bodies. The number, spacing, and orientation of working sections determine model resolution (for editing) and must be chosen based on the geometry of target anomalies.

WorldWind¶

WorldWind is an open-source virtual globe developed by NASA for geospatial data visualization. It allows users to interact with 3D representations of Earth and other celestial bodies, providing tools to overlay and analyze geospatial data, such as satellite imagery, terrain, and vector data. WorldWind is widely used in scientific research and GIS. In IGMAS+ WorldWind Java is is used for visualizing gravity and magnetic data on the globe.

X¶

XML (eXtensible Markup Language)¶

XML is a markup language used to encode documents in a format that is both human-readable and machine-readable. It defines rules for structuring data through tags and attributes, enabling hierarchical organization. XML documents can reference a DTD (Document Type Definition) to validate their structure, ensuring that the data conforms to predefined rules. This is crucial in web development, data exchange, and geophysical software for configuring models, storing metadata, and transmitting structured information.

Y¶

Z¶

0-10¶

3D Model¶

A representation of subsurface structures in three dimensions, based on geophysical data.