Glossary of Geophysical Terms
A |
B |
C |
D |
E |
F |
G |
H |
I |
J |
K |
L
M |
N |
O |
P |
Q |
R |
S |
T |
U |
V |
WXYZ
I
Imaging work station
Consists of a microcomputer with a high-resolution color monitor and accompanying software which allows the manipulation, enhancement and visual display of digital data.
Induced magnetization
Magnetization caused by an applied magnetic field. Contrast with remanent magnetization.
Induced polarization (IP)
A geophysical effect whereby electrical ge is momentarily polarized within a material, usually a disseminated ore or a clay. This effect is the basis for the IP method, in which a decaying voltage due to this polarization is measured following the turn-off of the activating current in time domain surveying. See also complex resistivity.
Induction (EM), induce
The process, described by Faraday’s Law, whereby a variable magnetic field generates an electric field (voltage) that, in the presence of a conductor, will produce electric currents.
Induction log
A method for measuring resistivity or conductivity that uses an electromagnetic technique to induce a flow of current in the rocks around a borehole; can be used in nonconductive-borehole fluids.
Induction number
A quantitative measure of the quality of a target for EM methods. The formulation varies for different targets but in general it involves the product of target conductivity, magnetic permeability, frequency of the transmitter and a cross-sectional dimension of the target. Dimensionless.
In-phase
That part of a periodic signal that has zero phase shift with a reference signal. See also quadrature.
Interpolation
A method to determine intermediate values from surrounding known values.
Interpretation
Transforming geophysical measurements into subsurface structure. More general term than inversion.
Interval transit time
The time required for a compressional acoustic wave to travel a unit distance (t); transit time usually is measured by acoustic or sonic logs, in microseconds per foot, and is the reciprocal of velocity.
Invaded zone
The annular interval of material around a drill hole where drilling fluid has replaced all or part of the native interstitial fluids.
Inversion, inverting
The process of deriving a model of the subsurface that is consistent with the geophysical data obtained. Generally refers to a more specific methodology than interpretation.
Isotopes
Atoms of the same element that have the same atomic number, but a different mass number; unstable isotopes are radioactive and decay to become stable isotopes.
