GEOPHYSICS

1. n. [Geophysics] Abbreviation for amplitude variation with offset and azimuth, the azimuthal variation of the AVO response. Alternate Form: amplitude variation with offset and azimuth See: amplitude variation with offset,  AVO

AVOAZ

1. n. [Geophysics] An axis of rotational invariance. A material whose properties exhibit cylindrical, or invariant rotational, symmetry may be rotated about this axis by any amount and its properties will be indistinguishable from what they were before the rotation.

axis of rotational symmetry

1. n. [Geophysics] A method for reconstructing the location and shape of the wave at an earlier time using the wave equation. Alternate Form: back-propagation

back propagation

1. n. [Geophysics] A modeling technique to assess the geologic history of rock layers through the use of geologic cross sections or seismic sections. Removal of the youngest layers of rock at the top of the section allows restoration of the underlying layers to their initial, undisturbed configurations. Successively older layers can be sequentially removed to further assess the effects of compaction, development of geologic structures, and other processes on an area. Alternate Form: back-stripping

back stripping

1. n. [Geophysics] A method for reconstructing the location and shape of the wave at an earlier time using the wave equation.

back-propagation

1. n. [Geophysics] A reflection phenomenon of energy in which a nonreflective surface, which is a surface that does not reflect energy coherently, randomly scatters energy. No coherent reflected energy can be identified and the energy is scattered in all directions, including back in the direction from which it came. For example, light can be scattered or redistributed by rough, nonreflective surfaces. See: deconvolution,  filter,  wave

backscatter

1. n. [Geophysics] A modeling technique to assess the geologic history of rock layers through the use of geologic cross sections or seismic sections. Removal of the youngest layers of rock at the top of the section allows restoration of the underlying layers to their initial, undisturbed configurations. Successively older layers can be removed sequentially to further assess the effects of compaction, development of geologic structures and other processes on an area. See: cross section

back-stripping

1. n. [Geophysics] A range of frequencies or wavelengths. Audible frequencies of sound and visible wavelengths of light are examples of bands. In seismic data, band-pass frequencies are within the limits of a specific filter, while band-reject frequencies exceed the acceptable range of frequencies. See: absorption band,  band-limited function,  filter,  frequency,  resolution,  wavelength

band

1. n. [Geophysics] Frequencies within the acceptable limits of a filter. The term is commonly used as an adjective, as in "band-pass filter," to denote a filter that passes a range of frequencies unaltered while rejecting frequencies outside the range. Alternate Form: band-pass

band pass

1. n. [Geophysics] Frequencies beyond the limits of a filter. Alternate Form: band-reject

band reject

1. n. [Geophysics] A function or time series whose Fourier transform is restricted to a finite range of frequencies or wavelengths. See: band,  frequency,  wavelength

band-limited function

1. n. [Geophysics] Frequencies within the acceptable limits of a filter. The term is commonly used as an adjective, as in "band-pass filter," to denote a filter that passes a range of frequencies unaltered while rejecting frequencies outside the range. Antonyms: band-reject See: band,  frequency

band-pass

1. n. [Geophysics] Frequencies beyond the limits of a filter. Antonyms: band-pass See: band,  frequency

band-reject

1. n. [Geophysics] The lower boundary of the near-surface, low-velocity zone in which rocks are physically, chemically, or biologically broken down, in some cases coincident with a water table. Static corrections to seismic data can compensate for the low velocity of the weathered layer in comparison with the higher-velocity strata below. See: first break,  ghost,  static correction,  velocity,  weathering

base of weathering

1. n. [Geophysics] A reference location for a survey, or a survey point whose measured values of a given parameter of interest are understood and can be used to normalize other survey points. Accurate knowledge of base stations is critical in gravity and magnetic surveying. See: baseline,  drift,  survey,  telluric-current method

base station

1. n. [Geophysics] A line joining base stations whose transmissions are synchronized during surveying. See: base station,  survey

baseline

1. n. [Geophysics] The shape of a wavelet produced by reflection of an actual wave train at one interface with a positive reflection coefficient. The embedded wavelet is useful for generating a convolutional model, or the convolution of an embedded wavelet with a reflectivity function and random noise, during seismic processing or interpretation. Synonyms: embedded wavelet See: reflection coefficient,  seismic processing

basic wavelet

1. n. [Geophysics] The 0 to 12 scale established by Admiral Francis Beaufort (1774 to 1857) for measurement of wind strength according to its effect on objects such as trees, flags, and water. According to the Beaufort scale, at wind speeds below 1 knot or 1 km/h, seas are calm. Whitecaps on water and blowing dust and leaves correspond to a Beaufort number of 4, with winds of 11 to 16 knots [20 to 28 km/h]. Hurricane-force winds, greater than 64 knots [> 118 km/h], have a Beaufort number of 12.

Beaufort scale

1. n. [Geophysics] The unit of measurement to describe or compare the intensity of acoustic or electrical signal, named for American inventor Alexander Graham Bell (1847 to 1922). Measurements are typically given in tenths of a bel, or decibels. The logarithm of the ratio of the sound or signal to a standard provides the decibel measurement. Sounds on the order of one decibel are barely audible to humans but can cause pain when on the order of 1012 decibels. The symbol for the unit is B, but dB is the standard unit. See: acoustic,  decibel,  signal

bel

1. n. [Geophysics] A permanently fixed marker cited in surveying, such as a concrete block or steel plate, with an inscription of location and elevation. Alternate Form: BM See: datum,  monument,  survey

benchmark