GEOPHYSICS

1. n. [Geophysics] A device used in surface seismic acquisition, both onshore and on the seabed offshore, that detects ground velocity produced by seismic waves and transforms the motion into electrical impulses. Geophones detect motion in only one direction. Conventional seismic surveys on land use one geophone per receiver location to detect motion in the vertical direction. Three mutually orthogonal geophones are typically used in combination to collect 3C seismic data. Hydrophones, unlike geophones, detect changes in pressure rather than motion. Synonyms: jug,  receiver,  seismometer See: accelerometer,  array,  cable,  channel,  check-shot survey,  coupling,  damping,  datum correction,  detector,  displacement,  downhole receiver,  dropout,  fan shooting,  first break,  four-component seismic data,  geophone interval,  ground roll,  group interval,  hodogram,  hydrophone,  image,  jug hustler,  multicomponent seismic data,  nest,  ocean-bottom cable,  random noise,  seismograph,  spread,  three-component seismic data,  velocity analysis

geophone

1. n. [Geophysics] A geometrical arrangement of seismic receivers (geophones) with signals recorded by one channel. The array can contain numerous closely spaced geophones. See: array,  fan shooting,  footprint,  geophone,  ground roll,  hydrophone,  radial array,  receiver,  seismic trace,  source,  source pattern,  spread

geophone array

1. n. [Geophysics] A bundle of electrical wires that connects geophones and relays data to the seismic recording truck or seismic vessel. See: cable,  channel,  eel,  geophone,  hydrophone,  jug hustler,  ocean-bottom cable,  spacer,  streamer

geophone cable

1. n. [Geophysics] The distance between geophones or the centers of groups of geophones. Synonyms: group interval See: geophone,  group,  source

geophone interval

1. n. [Geophysics] In surface seismic acquisition, the horizontal distance from source to geophone. In a vertical seismic profile, geophone offset is the horizontal distance between the source and the wellhead or the surface projection of the geophone in the case of a deviated well. Offset between seismic source and receiver creates a delay, or moveout, in the arrival time of a reflection that can be corrected before stacking and can be used to determine velocity. See: acquisition,  arrival time,  common-offset,  extended spread,  fold,  lithostratigraphic inversion,  moveout,  mute,  normal moveout,  offset,  perpendicular offset,  shotpoint,  spread,  tail mute,  two-way traveltime,  velocity analysis,  vertical seismic profile,  walkaway vertical seismic profile,  zero-offset data

geophone offset

1. n. [Geophysics] A geometrical arrangement of seismic receivers (geophones) with signals recorded by one channel. The array can contain numerous closely spaced geophones. See: array,  fan shooting,  footprint,  geophone,  ground roll,  hydrophone,  radial array,  receiver,  seismic trace,  source,  source pattern,  spread

geophone pattern

1. n. [Geophysics] A scientist trained in the study of the physics of the Earth, particularly its electrical, gravitational and magnetic fields and propagation of elastic (seismic) waves within it. In the petroleum industry, geophysicists perform a variety of functions, chiefly the processing and interpretation of seismic data and generation of subsurface maps on the basis of seismic data. Such interpretations enhance understanding of subsurface geology. See: elastic wave,  seismic wave

geophysicist

1. n. [Geophysics] The study of the physics of the Earth, especially its electrical, gravitational and magnetic fields and propagation of elastic (seismic) waves within it. Geophysics plays a critical role in the petroleum industry because geophysical data are used by exploration and development personnel to make predictions about the presence, nature and size of subsurface hydrocarbon accumulations. See: acoustic,  gravity,  magnetics,  seismic,  seismic wave

geophysics

1. n. [Geophysics] A short-path multiple, or a spurious reflection that occurs when seismic energy initially reverberates upward from the shallow subsurface and then is reflected downward, such as at the base of weathering or between sources and receivers and the sea surface. See: base of weathering,  multiple reflection,  receiver,  short-path multiple,  source

ghost

1. n. [Geophysics] The ringing near a discontinuity in a signal that is caused by incomplete Fourier synthesis, or missing frequencies. See: Fourier analysis,  Fourier synthesis,  frequency

Gibbs' phenomenon

1. n. [Geophysics] A device used to measure the acceleration due to gravity, or, more specifically, variations in the gravitational field between two or more points. See: detector,  gravimetry

gravimeter

1. n. [Geophysics] The measurement of gravity or the study of its variations. See: gravimeter,  gravity

gravimetry

1. n. [Geophysics] The Earth's gravitational field, or the attractive force produced by the mass of the Earth. Variations in the gravitational field can be used to map changes in the density of formations in the Earth. Gravity surveys can be used to map the extent or depth of sedimentary basins or even individual hydrocarbon prospects. See: anomaly,  Bouguer anomaly,  Bouguer correction,  caprock effect,  deep tow,  density contrast,  density profile,  downward continuation,  free-air correction,  geophysics,  gravimeter,  gravimetry,  gravity anomaly,  isostatic correction,  potential field,  remote sensing,  spherical divergence,  upward continuation

gravity

1. n. [Geophysics] The difference between the actual value of gravity measured at a location and the value predicted by a particular Earth model. Gravity anomalies are usually determined by adjusting the known value of (absolute) gravity at a reference station by Bouguer, free-air or other corrections and subtracting the final predicted value from the measurement. (A different description is that the various corrections are subtracted from the data to reduce it to the reference level. Both interpretations are valid provided it is remembered that the resulting gravity anomaly can be caused by density anomalies—i.e., differences in density between Earth and the theoretical model—that can lie anywhere either above or below the reference level.) See: anomaly,  Bouguer correction,  free-air correction,  gravity

gravity anomaly

1. n. [Geophysics] The measurement of gravitational acceleration over an area, usually presented as a map or profile of Bouguer or free-air anomalies. See: Bouguer anomaly,  free-air correction,  survey

gravity survey

1. n. [Geophysics] A regular spatial arrangement of points, such as x-y coordinates.

grid

1. n. [Geophysics] A type of coherent noise generated by a surface wave, typically a low-velocity, low-frequency, high-amplitude Rayleigh wave. Ground roll can obscure signal and degrade overall data quality, but can be alleviated through careful selection of source and geophone arrays, filters and stacking parameters. See: acquisition,  array,  coherent noise,  mute,  random noise,  Rayleigh wave,  stack,  surface wave,  tail mute,  water-bottom roll

ground roll

1. n. [Geophysics] A set of seismometers whose output is sent to a common data channel to record a seismic trace. A large group is known as a patch. See: fold,  geophone interval,  group interval,  patch,  seismic trace,  seismometer,  spread

group

1. n. [Geophysics] The distance between geophones or groups of geophones. Synonyms: geophone interval See: geophone,  group,  source,  spacing

group interval

1. n. [Geophysics] The velocity that wave energy—comprised of a wave group, train or packet of individual wave phases or components—travels through a medium. The wave energy may be grouped into an envelope that is shrink-wrapped around it. The shape of the envelope around the wave-energy group changes with distance because the individual wave phases move apart from one another. vg = vp − λ (∂vp/∂λ) = vp + f (∂vp/∂f) Relation of group velocity to phase velocity. As a wave travels through a medium, its energy moves at the group velocity (vg) and its individual phases, or components, move at their phase velocity (vp). The wave changes shape with distance as each frequency (f), or wavelength (λ), component moves at its separate phase velocity through the phenomenon of dispersion. Relative to the group velocity, each component moves with faster or slower phase velocity, depending on how phase velocity changes with wavelength or frequency. See: phase velocity

group velocity