GEOPHYSICS

Question 1

A single seismic trace.

Answer 1

1-D seismic data

Question 2

A check-shot survey of a well, which can be used to correct the sonic log and generate a synthetic seismogram that displays changes in amplitude versus traveltime.

Answer 2

1-D seismic data

Question 3

A vertical section of seismic data consisting of numerous adjacent traces acquired sequentially.

Answer 3

2D seismic data

Question 4

A group of 2D seismic lines acquired individually, as opposed to the multiple closely spaced lines acquired together that constitute 3D seismic data.

Answer 4

2D seismic data

Question 5

Seismic data or a group of seismic lines acquired individually such that there typically are significant gaps (commonly 1 km or more) between adjacent lines. A 2D survey typically contains numerous lines acquired orthogonally to the strike of geological structures (such as faults and folds) with a minimum of lines acquired parallel to geological structures to allow line-to-line tying of the seismic data and interpretation and mapping of structures.

Answer 5

2D survey

Question 6

A type of multicomponent seismic data acquired in a land, marine, or borehole environment by using three orthogonally oriented geophones or accelerometers. 3C is particularly appropriate when the addition of a hydrophone (the basis for 4C seismic data) adds no value to the measurement, as for example, on land. This technique allows determination of both the type of wave and its direction of propagation.

Answer 6

3C seismic data

Question 7

A set of numerous closely-spaced seismic lines that provide a high spatially sampled measure of subsurface reflectivity. Typical receiver line spacing can range from 300 m [1000 ft] to over 600 m [2000 ft], and typical distances between shotpoints and receiver groups is 25 m [82 ft] (offshore and internationally) and 110 ft or 220 ft [34 to 67 m] (onshore USA, using values that are even factors of the 5280 feet in a mile). Bin sizes are commonly 25 m, 110 ft or 220 ft. The resultant data set can be “cut” in any direction but still display a well sampled seismic section. The original seismic lines are called in-lines. Lines displayed perpendicular to in-lines are called crosslines. In a properly migrated 3D seismic data set, events are placed in their proper vertical and horizontal positions, providing more accurate subsurface maps than can be constructed on the basis of more widely spaced 2D seismic lines, between which significant interpolation might be necessary. In particular, 3D seismic data provide detailed information about fault distribution and subsurface structures. Computer-based interpretation and display of 3D seismic data allow for more thorough analysis than 2D seismic data.

Answer 7

3D seismic data

Question 8

The acquisition of seismic data as closely spaced receiver and shot lines such that there typically are no significant gaps in the subsurface coverage. A 2D survey commonly contains numerous widely spaced lines acquired orthogonally to the strike of geological structures and a minimum of lines acquired parallel to geological structures to allow line-to-line correlation of the seismic data and interpretation and mapping of structures.

Answer 8

3D survey

Question 9

Four-component (4C) borehole or marine seismic data are typically acquired using three orthogonally-oriented geophones and a hydrophone within an ocean-bottom sensor (deployed in node-type systems as well as cables). Provided the system is in contact with the seabed or the borehole wall, the addition of geophones allows measurement of shear (S) waves, whereas the hydrophone measures compressional (P) waves.

Answer 9

4C seismic data

Question 10

Three-dimensional (3D) seismic data acquired at different times over the same area to assess changes in a producing hydrocarbon reservoir with time. Changes may be observed in fluid location and saturation, pressure and temperature. 4D seismic data is one of several forms of time-lapse seismic data. Such data can be acquired on the surface or in a borehole.

Answer 10

4D seismic data

Question 11

A term to indicate features in seismic data other than reflections, including events such as diffractions, multiples, refractions and surface waves. Although the term suggests that such events are not common, they often occur in seismic data.

Answer 11

abnormal events

Question 12

The range of wavelengths of energy that can be absorbed by a given substance.

Answer 12

absoprtion band

Question 13

An algorithm used in numerical simulation along the boundary of a computational domain to absorb all energy incident upon that boundary and to suppress reflection artifacts.

Answer 13

absorbing boundary conditions

Question 14

The ratio of absorbed incident energy to the total energy to which a body is exposed.

Answer 14

absorptance

Question 15

The property of some liquids or solids to soak up water or other fluids. The natural gas dehydration process uses glycols (liquids) that absorb the water vapor to finally obtain dehydrated gas. In the same way, light oil, also called absorption oil, is used to remove the heavier liquid hydrocarbons from a wet gas stream to obtain dry gas.

Answer 15

absorption

Question 16

The conversion of one form of energy into another as the energy passes through a medium. For example, seismic waves are partially converted to heat as they pass through rock.

Answer 16

absorption

Question 17

A device used during surveying to measure the acceleration of a ship or aircraft, or to detect ground acceleration in boreholes or on the Earth’s surface produced by acoustic vibrations.

Answer 17

accelerometer

Question 18

Pertaining to sound. Generally, acoustic describes sound or vibrational events, regardless of frequency. The term sonic is limited to frequencies and tools operated in the frequency range of 1 to 25 kilohertz.

Answer 18

acoustic

Question 19

In geophysics, acoustic refers specifically to P-waves in the absence of S-waves (i.e., in fluids, which do not support S-waves, or in cases in which S-waves in solids are ignored).

Answer 19

acoustic

Question 20

An obsolete piece of equipment that converts acoustic signals from analog to electrical form and back. A common use of an acoustic coupler was to provide an interface between a telephone and an early type of computer modem.

Answer 20

acoustic coupler

Question 21

A type of elastic wave produced by deformation or brittle failure of material and characterized by relatively high frequency.

Answer 21

acoustic emission

Question 22

The product of density and seismic velocity, which varies among different rock layers, commonly symbolized by Z. The difference in acoustic impedance between rock layers affects the reflection coefficient.

Answer 22

acoustic impedance

Question 23

A seismic reflectivity section, or a 2D or 3D seismic section, that has been inverted for acoustic impedance. Sonic and density logs can be used to calibrate acoustic impedance sections.

Answer 23

acoustic impedance section

Question 24

A display of traveltime of acoustic waves versus depth in a well. The term is commonly used as a synonym for a sonic log. Some acoustic logs display velocity.

Answer 24

acoustic log

Question 25

A record of some acoustic property of the formation or borehole. The term is sometimes used to refer specifically to the sonic log, in the sense of the formation compressional slowness. However, it may also refer to any other sonic measurement, for example shear, flexural and Stoneley slownesses or amplitudes, or to ultrasonic measurements such as the borehole televiewer and other pulse-echo devices, and even to noise logs.

Answer 25

acoustic log / acoustic velocity log

Question 26

A method of calculating the position of marine seismic equipment. Range measurements are made whereby distance is equal to acoustic signal traveltime from transmitter to hydrophone multiplied by the speed of sound in water. When sufficient acoustic ranges with a proper geometric distribution are collected, location coordinates x, y and z of the marine seismic equipment can be computed by the method of trilateration (measuring the lengths of the sides of overlapping triangles). Acoustic positioning is commonly used in towed streamer and ocean-bottom cable seismic acquisition modes.

Answer 26

acoustic positioning

Question 27

The quality of a medium whose acoustic impedance is constant throughout, such that it contains no seismic reflections. An example of an acoustically transparent medium is water.

Answer 27

acoustic transparency

Question 28

The duration of the passage of a signal from the source through the Earth and back to the receiver. A time seismic section typically shows the two-way traveltime of the wave.

Answer 28

acoustic traveltime

Question 29

The rate at which a sound wave travels through a medium. Unlike the physicist's definition of velocity as a vector, its usage in geophysics is as a property of a medium: distance divided by traveltime. Velocity can be determined from laboratory measurements, acoustic logs, vertical seismic profiles or from velocity analysis of seismic data. It can vary vertically, laterally and azimuthally in anisotropic media such as rocks, and tends to increase with depth in the Earth because compaction reduces porosity. Velocity also varies as a function of how it is derived from the data. For example, the stacking velocity derived from normal moveout measurements of common depth point gathers differs from the average velocity measured vertically from a check-shot or vertical seismic profile (VSP). Velocity would be the same only in a constant-velocity (homogeneous) medium.

Answer 29

acoustic velocity

Question 30

A display of traveltime of acoustic waves versus depth in a well. The term is commonly used as a synonym for a sonic log. Some acoustic logs display velocity.

Answer 30

acoustic velocity log

Question 31

An elastic body wave or sound wave in which particles oscillate in the direction the wave propagates. P-waves are the waves studied in conventional seismic data. P-waves incident on an interface at other than normal incidence can produce reflected and transmitted S-waves, in that case known as converted waves.

Answer 31

acoustic wave / dilatational wave

Question 32

The generation and recording of seismic data. Acquisition involves many different receiver configurations, including laying geophones or seismometers on the surface of the Earth or seafloor, towing hydrophones behind a marine seismic vessel, suspending hydrophones vertically in the sea or placing geophones in a wellbore (as in a vertical seismic profile) to record the seismic signal. A source, such as a vibrator unit, dynamite shot, or an air gun, generates acoustic or elastic vibrations that travel into the Earth, pass through strata with different seismic responses and filtering effects, and return to the surface to be recorded as seismic data. Optimal acquisition varies according to local conditions and involves employing the appropriate source (both type and intensity), optimal configuration of receivers, and orientation of receiver lines with respect to geological features. This ensures that the highest signal-to-noise ratio can be recorded, resolution is appropriate, and extraneous effects such as air waves, ground roll, multiples and diffractions can be minimized or distinguished, and removed through processing.

Answer 32

acquisition

Question 33

The surface or near-surface, unconsolidated sedimentary layer that has been subject to weathering and whose pores are air-filled instead of liquid-filled. An aerated layer typically has a low seismic velocity.

Answer 33

aerated layer

Question 34

Measurements of the Earth's magnetic field gathered from aircraft. Magnetometers towed by an airplane or helicopter can measure the intensity of the Earth's magnetic field. The differences between actual measurements and theoretical values indicate anomalies in the magnetic field, which in turn represent changes in rock type or in thickness of rock units.

Answer 34

aeromagnetic survey

Question 35

Abbreviation for automatic gain control. A system to automatically control the gain, or the increase in the amplitude of an electrical signal from the original input to the amplified output. AGC is commonly used in seismic processing to improve visibility of late-arriving events in which attenuation or wavefront divergence has caused amplitude decay.

Answer 35

AGC

Question 36

The exponential rate constant (τ) that determines how quickly the output amplitude of an electrical signal that is under automatic gain control (AGC) responds to a sudden increase or decrease in input signal amplitude. Mathematically, Af(t) = Ai(t) + ΔAi (1 − e−t/τ) , where Af is the output signal amplitude, Ai is the input signal amplitude (Ai), ΔAi is the change in input signal amplitude and t is time. When t equals τ, the function (1 − e−t/τ) equals (1 − 1/e) equals 0.63. Therefore, the AGC time constant (τ) is the amount of time that elapses for the output signal of AGC to reflect 63% of the change in the input signal amplitude.

Answer 36

AGC time constant

Question 37

A source of seismic energy used in acquisition of marine seismic data. This gun releases highly compressed air into water. Air guns are also used in water-filled pits on land as an energy source during acquisition of vertical seismic profiles.

Answer 37

air gun

Question 38

A method of seismic acquisition using charges detonated in the air or on poles above the ground as the source. Air shooting is also called the Poulter method after American geophysicist Thomas Poulter.

Answer 38

air shooting

Question 39

A sound wave that travels through the air at approximately 330 m/s and can be generated and recorded during seismic surveying. Air waves are a type of coherent noise.

Answer 39

air wave

Question 40

A filter, or a set of limits used to eliminate unwanted portions of the spectra of the seismic data, to remove frequencies that might cause aliasing during the process of sampling an analog signal during acquisition or when the sample rate of digital data is being decreased during seismic processing.

Answer 40

alias filter

Question 41

The distortion of frequency introduced by inadequately sampling a signal, which results in ambiguity between signal and noise. Aliasing can be avoided by sampling at least twice the highest frequency of the waveform or by filtering frequencies above the Nyquist frequency, the highest frequency that can be defined accurately by that sampling interval.

Answer 41

aliasing

Question 42

The difference between the maximum displacement of a wave and the point of no displacement, or the null point. The common symbol for amplitude is a.

Answer 42

amplitude

Question 43

An abrupt increase in seismic amplitude that can indicate the presence of hydrocarbons, although such anomalies can also result from processing problems, geometric or velocity focusing or changes in lithology. Amplitude anomalies that indicate the presence of hydrocarbons can result from sudden changes in acoustic impedance, such as when a gas sand underlies a shale, and in that case, the term is used synonymously with hydrocarbon indicator.

Answer 43

amplitude anomaly / bright spot

Question 44

A change in the amplitude of a waveform that is generally undesirable, such as in seismic waves.

Answer 44

amplitude distortion

Question 45

The inability of a system to exactly match input and output amplitude, a general example being an electronic amplifier and the classic example being a home stereophonic amplifier.

Answer 45

amplitude distortion

Question 46

The azimuthal variation of the AVO response.

Answer 46

amplitude variation with offset and azimuth / AVOAZ

Question 47

Variation in seismic reflection amplitude with change in distance between shotpoint and receiver that indicates differences in lithology and fluid content in rocks above and below the reflector. AVO analysis is a technique by which geophysicists attempt to determine thickness, porosity, density, velocity, lithology and fluid content of rocks. Successful AVO analysis requires special processing of seismic data and seismic modeling to determine rock properties with a known fluid content. With that knowledge, it is possible to model other types of fluid content. A gas-filled sandstone might show increasing amplitude with offset, whereas a coal might show decreasing amplitude with offset. A limitation of AVO analysis using only P-energy is its failure to yield a unique solution, so AVO results are prone to misinterpretation. One common misinterpretation is the failure to distinguish a gas-filled reservoir from a reservoir having only partial gas saturation ("fizz water"). However, AVO analysis using source-generated or mode-converted shear wave energy allows differentiation of degrees of gas saturation. AVO analysis is more successful in young, poorly consolidated rocks, such as those in the Gulf of Mexico, than in older, well-cemented sediments.

Answer 47

amplitude variation with offset/ AVO

Question 48

The acute angle at which a wavefront impinges upon an interface, such as a seismic wave impinging upon strata. Normal incidence is the case in which the angle of incidence is zero, the wavefront is parallel to the surface and its raypath is perpendicular, or normal, to the interface. Snell's law describes the relationship between the angle of incidence and the angle of refraction of a wave.

Answer 48

angle of approach

Question 49

The acute angle at which a raypath impinges upon a line normal to an interface, such as a seismic wave impinging upon strata. Normal incidence is the case in which the angle of incidence is zero, the wavefront is parallel to the surface and its raypath is perpendicular, or normal, to the interface. Snell's law describes the relationship between the angle of incidence and the angle of refraction of a wave.

Answer 49

angle of incidence

Question 50

The variation of seismic velocity in different directions.

Answer 50

angular dispersion / seismic velocity

Question 51

Having directionally dependent properties. For a crystal of a mineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, anisotropy is common in shales.

Answer 51

anisotropic

Question 52

Predictable variation of a property of a material with the direction in which it is measured, which can occur at all scales. For a crystal of a mineral, variation in physical properties observed in different directions is anisotropy. In rocks, variation in seismic velocity measured parallel or perpendicular to bedding surfaces is a form of anisotropy. Often found where platy minerals such as micas and clays align parallel to depositional bedding as sediments are compacted, anisotropy is common in shales.

Answer 52

anisotropy/ aeolotropy

Question 53

A filter, or a set of limits used to eliminate unwanted portions of the spectra of the seismic data, to remove frequencies that might cause aliasing during the process of sampling an analog signal during acquisition or when the sample rate of digital data is being decreased during seismic processing.

Answer 53

antialias filter

Question 54

A portion of a data set, such as seismic data, to which functions or filters are applied. Aperture time, for example, can be specified, such as a window from 1.2 to 2.8 seconds.

Answer 54

aperture/ window

Question 55

A mechanism to limit the affects of measurements on a device or system. In seismic data acquisition, the length of the spread has the effect of an aperture.

Answer 55

aperture/ window

Question 56

In seismic data, the ratio of the velocity determined from normal moveout (i.e., primarily a horizontal measurement) to velocity measured vertically in a vertical seismic profile or similar survey. Apparent anisotropy is of particular importance when migrating long-offset seismic data and analyzing AVO data accurately. The normal moveout velocity involves the horizontal component of the velocity field, which affects sources and receivers that are offset, but the horizontal velocity field is not involved in velocity calculations from vertically measured time-depth pairs.

Answer 56

apparent anisotropy

Question 57

In geophysics, the velocity of a wavefront in a certain direction, typically measured along a line of receivers and symbolized by va. Apparent velocity and velocity are related by the cosine of the angle at which the wavefront approaches the receivers: va = v cos θ, whereva = apparent velocityv = velocity of wavefrontθ = angle at which a wavefront approaches the geophone array.

Answer 57

apparent velocity

Question 58

The wavelength measured by receivers when a wave approaches at an angle. The relationship between true and apparent wavelength can be shown mathematically as follows: λ = λa sin θ, whereλ = wavelengthλa = apparent wavelengthθ = angle at which a wavefront approaches the geophone array.

Answer 58

apparent wavelength

Question 59

A technique to map a potential field generated by stationary electrodes by moving an electrode around the survey area.

Answer 59

applied-potential method

Question 60

In computing, code written to access data in more than one dimension according to a name and subscripts that correspond to each dimension.

Answer 60

array

Question 61

A geometrical arrangement of seismic sources (a source array, with each individual source being activated in some fixed sequence in time) or receivers (a hydrophone or geophone array) that is recorded by one channel.

Answer 61

array

Question 62

An arrangement or configuration of electrodes or antennas used for resistivity, induced polarization (IP), or other types of electromagnetic surveying. Resistivity arrays typically consist of two current electrodes and two potential electrodes and are distinguished by the relative separations between the electrodes. Examples are the dipole-dipole, Schlumberger and Wenner arrays.

Answer 62

array

Question 63

Generally, a geometrical configuration of transducers (sources or receivers) used to generate or record a physical field, such as an acoustic or electromagnetic wavefield or the Earth's gravity field.

Answer 63

array/ nest

Question 64

The elapsed time between the release of seismic energy from a source and its arrival at the receiver.

Answer 64

arrival time

Question 65

The removal of undesirable features, such as multiple events, from seismic data.

Answer 65

attenuate/ attenuation

Question 66

The loss of energy or amplitude of waves as they pass through media. Seismic waves lose energy through absorption, reflection and refraction at interfaces, mode conversion and spherical divergence, or spreading of the wave.

Answer 66

attenuation

Question 67

The reduction in amplitude of an electromagnetic wave passing through the formation, usually measured in decibels/meter, dB/m. The term is used in particular with reference to the propagation resistivity log and the electromagnetic propagation log.

Answer 67

attenuation/ attenuate

Question 68

A measurable property of seismic data, such as amplitude, dip, frequency, phase and polarity. Attributes can be measured at one instant in time or over a time window, and may be measured on a single trace, on a set of traces or on a surface interpreted from seismic data. Attribute analysis includes assessment of various reservoir parameters, including ahydrocarbon indicator, by techniques such as amplitude variation with offset (AVO) analysis.

Answer 68

attribute

Question 69

The comparison of a waveform to itself. Autocorrelation is useful in the identification of multiples or other regularly repeating signals, and in designing deconvolution filters to suppress them.

Answer 69

autocorrelation

Question 70

A system to control the gain, or the increase in the amplitude of an electrical signal from the original input to the amplified output, automatically. AGC is commonly used in seismic processing to improve visibility of late-arriving events in which attenuation or wavefront divergence has caused amplitude decay.

Answer 70

automatic gain control

Question 71

To use computer software to pick a particular reflection or attribute in seismic data automatically. Autotracking can speed interpretation of three-dimensional seismic data, but must be checked for errors, especially in areas of faulting and stratigraphic changes.

Answer 71

autotrack

Question 72

Use of computer software to pick a particular reflection or attribute in seismic data automatically. Autotracking can speed interpretation of three-dimensional seismic data, but must be checked for errors, especially in areas of faulting and stratigraphic changes.

Answer 72

autotracking

Question 73

Abbreviation for amplitude variation with angle of incidence.

Answer 73

AVA

Question 74

Abbreviation for amplitude variation with azimuth.

Answer 74

AVAZ

Question 75

In geophysics, the depth divided by the traveltime of a wave to that depth. Average velocity is commonly calculated by assuming a vertical path, parallel layers and straight raypaths, conditions that are quite idealized compared to those actually found in the Earth.

Answer 75

average velocity

Question 76

Abbreviation for amplitude variation with offset. Variation in seismic reflection amplitude with change in distance between shotpoint and receiver that indicates differences in lithology and fluid content in rocks above and below the reflector. AVO analysis is a technique by which geophysicists attempt to determine thickness, porosity, density, velocity, lithology and fluid content of rocks. Successful AVO analysis requires special processing of seismic data and seismic modeling to determine rock properties with a known fluid content. With that knowledge, it is possible to model other types of fluid content. A gas-filled sandstone might show increasing amplitude with offset, whereas a coal might show decreasing amplitude with offset. A limitation of AVO analysis using only P-energy is its failure to yield a unique solution, so AVO results are prone to misinterpretation. One common misinterpretation is the failure to distinguish a gas-filled reservoir from a reservoir having only partial gas saturation ("fizz water"). However, AVO analysis using source-generated or mode-converted shear wave energy allows differentiation of degrees of gas saturation. AVO analysis is more successful in young, poorly consolidated rocks, such as those in the Gulf of Mexico, than in older, well-cemented sediments.

Answer 76

AVO / amplitude variation with offset

Question 77

Abbreviation for amplitude variation with offset and azimuth. The azimuthal variation of the AVO response.

Answer 77

AVOAZ/ amplitude variation with offset and azimuth

Question 78

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.

Answer 78

axis of rotational symmetry

Question 79

A method for reconstructing the location and shape of the wave at an earlier time using the wave equation.

Answer 79

back propagation

Question 80

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.

Answer 80

back stripping

Question 81

A method for reconstructing the location and shape of the wave at an earlier time using the wave equation.

Answer 81

back-propagation

Question 82

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.

Answer 82

backscatter

Question 83

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.

Answer 83

band

Question 84

A function or time series whose Fourier transform is restricted to a finite range of frequencies or wavelengths.

Answer 84

band-limited function

Question 85

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.

Answer 85

band-pass

Question 86

Frequencies beyond the limits of a filter.

Answer 86

band-reject

Question 87

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.

Answer 87

base of weathering

Question 88

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.

Answer 88

base station

Question 89

A line joining base stations whose transmissions are synchronized during surveying.

Answer 89

baseline

Question 90

A reference line, such as a "shale baseline," a line representing the typical value of a given measurement for a shale on a well log, or the zero-amplitude line of a seismic trace.

Answer 90

baseline

Question 91

The original survey of a set of surveys covering the same area but acquired over a period of time. In four-dimensional seismic data, it is the first seismic survey, which is then compared to subsequent surveys.

Answer 91

baseline

Question 92

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.

Answer 92

basic wavelet/ embedded wavelet

Question 93

The 0 to 12 scale for measurement of wind strength according to its effect on objects such as trees, flags and water established by Admiral Francis Beaufort (1774 to 1857). According to the Beaufort scale, at wind speeds below 1 knot or 1 km/hr, 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/hr]. Hurricane-force winds, greater than 64 knots [> 118 km/hr], have a Beaufort number of 12.

Answer 93

Beaufort scale

Question 94

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.

Answer 94

bel

Question 95

A permanently fixed marker cited in surveying, such as a concrete block or steel plate, with an inscription of location and elevation.

Answer 95

benchmark/ BM

Question 96

A standard against which the performance of processes are measured.

Answer 96

benchmark/ BM

Question 97

An adjustment of the relative positive and negative excursions of reflections during seismic processing by bulk shifting the null point, or baseline, of the data to emphasize peaks at the expense of troughs or vice versa. Some authors describe bias as a systematic distortion of seismic data to achieve greater continuity.

Answer 97

bias

Question 98

To sort seismic data into small areas according to the midpoint between the source and the receiver, reflection point or conversion point prior to stacking.

Answer 98

bin

Question 99

A subdivision of a seismic survey. The area of a three-dimensional survey is divided into bins, which are commonly on the order of 25 m [82 ft] long and 25 m wide; traces are assigned to specific bins according to the midpoint between the source and the receiver, reflection point or conversion point. Bins are commonly assigned according to common midpoint (CMP), but more sophisticated seismic processing allows for other types of binning. Traces within a bin are stacked to generate the output trace for that bin. Data quality depends in part on the number of traces per bin, or the fold.

Answer 99

bin

Question 100

A device containing a magnetometer and possibly other instruments that can be towed by an aircraft during aeromagnetic surveying or in a marine seismic streamer to provide dynamic information about the streamer position.

Answer 100

bird