Residual Gravity Field


The shorter wavelength component of the attributed to density Bouguer gravity field contrasts within high density basement and/or the lower density overburden. Anomalies in the residual field are usually of exploration interest. A first residual is a difference field obtained by subtracting the regional gravity field from the Bouguer gravity field.



The degree of homogeneity in Euler's equation, interpreted physically as the fall-off rate with distance and geophysically as a structural index (SI). Values vary from 1 to 3 according to magnetic or gravity source body geometry.



An SI unit measuring magnetic flux. 1 weber = 1 tesla-m2 = 105 gauss-m2 = 109 gamma-m2 = 109 nT-m2

Three Dimensional (3D) Model


Networks or grids of values which model geologic surfaces represented by surfaces of density (gravity) or susceptibility (magnetics) contrast. The output of a forward model is the combined calculated gravity or magnetic effect of the specified input surfaces. See also Inverse Modeling.

Tesla (T)


An SI unit measuring magnetic flux density. 1 tesla = 109 nanotesla. A cgs unit for stating the magnitude of the magnetic field vector B represented by the number of lines of induction passing through a unit area perpendicular to the vector direction. 1 tesla  = 109 gamma = 108 lines/m2 = 1 weber/m2 = 109 nanotesla



A measure of the degree to which a substance may be magnetized. It is a ratio k of the intensity of magnetization I to the causative magnetic field H. It is typically expressed in micro cgs units for oil and gas exploration work. Susceptibility has been shown to be proportional to the volume percentage of magnetite contained in a rock. Susceptibility contrast is the susceptibility [...]

Structural Model (2D or 2½D)


A gravity or magnetic structural model is a 2D or 2½D density and/or susceptibility model of given or assumed geology. The geology of an area can be modeled by representing lithologic layers as equi-density and/or equi-susceptibility layers and/or blocks. The layers are formed by contrast boundaries, which may or may not correspond to specific geologic formation boundaries. Where high density or susceptibility contrasts exist in [...]

Structural Index


The Euler deconvolution and Half-Slope Method techniques use first-order derivatives to determine magnetically-based depth estimations for idealized targets, such as sphere, cylinder, thin dike, contact edge.  Each of these targets is characterized by a specific structural index (N)


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