Glossary of Geophysical Terms
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B |
C |
D |
E |
F |
G |
H |
I |
J |
K |
L
M |
N |
O |
P |
Q |
R |
S |
T |
U |
V |
WXYZ
M
M electrode
The potential electrode nearest to the A electrode in a resistivity device.
Magnetics, geomagnetics
Geophysical methodology for studying anomalies in the geomagnetic field due to non-uniform magnetization of the subsurface. Uses magnetometers.
Magnetic permeability
acteristic of a material, it is proportional to the magnetism induced in that material divided by strength of the magnetic field used.
Magnetic susceptibility
A measure of the extent to which a substance may be magnetized; it represents the ratio of magnetization to magnetic field strength.
Magnetization
The magnetic moment per unit volume. It is a vector quantity. See also magnetic susceptibility.
Magnetometer
A device for measuring the earth's magnetic geomagnetic field. Variations in the field strength may indicate changes in magnetic properties of soil and rock or presence of ferrous metals.
Mapping
Locating geological, chemical or geophysical information in space (as opposed to time, which is monitoring). The results are usually summarized as maps.
Matrix
The solid framework of rock or mineral grains that surrounds the pore spaces.
Mho
A unit of electrical conductance that is the reciprocal of ohm.
Micro-gravity survey
A surface geophysical survey method, undertaken on a very small scale (typically station spacings of a few meters), and requiring a high meter sensitivity. Measures the earth's gravitational field at different points over an area of interest. Variations in the field are related to differences in subsurface density distributions, which in turn are associated with changes in soil, rock, and cultural factors. Typically used for cavern or fracture detection.
Microresistivity log
Refers to a group of short-spaced resistivity logs that are used to make measurements of the mud cake and invaded zone.
Migration
The movement of chemicals, bacteria, gases, etc. in flowing water or vapor in the subsurface. Also, a seismic/radar term whose general meaning is the correction of the recorded image for the effects of reflector dip. A very typical result of migration is the removal of hyperbolic events on the record resulting from diffractions from faults and other discontinuities.
Monitoring
Observing the change in a geophysical, hydrogeological or geochemical measurement with time.
Mud cake
Also called filter cake; the layer of mud particles that builds up on the wall of a rotary-drilled hole as mud filtrate is lost to the formation.
Mud filtrate
The liquid effluent of drilling mud that penetrates the wall of the hole.
Muting
Change in the amplitude of all or part of a trace before additional processing. Noisy or clearly erroneous traces are given zero amplitude. Data before the first break and the known refraction arrivals are also often reduced to zero amplitude.
