GEOPHYSICS

1. n. [Geophysics] A method of adjusting a dataset against a control that has properties to which the dataset should conform. See: fan shooting

calibration

1. n. [Geophysics] A small, electrically activated explosive charge that detonates a larger charge. Caps, also called seismic caps or blasting caps, are used for seismic acquisition with an explosive source to achieve consistent timing of detonation. Alternate Form: blasting cap See: detonator

cap

1. n. [Geophysics] A type of positive gravity anomaly that results from the presence of a dense cap rock overlying a relatively low-density salt dome. See: caprock

caprock effect

1. n. [Geophysics] An implosion produced by locally low pressure, such as the collapse of a gas bubble in liquid (the energy of which is used as the source of seismic energy from air guns). See: air gun,  bubble effect,  water gun

cavitation

1. n. [Geophysics] In multichannel seismic acquisition where beds do not dip, the common reflection point at depth on a reflector, or the halfway point when a wave travels from a source to a reflector to a receiver. In the case of flat layers, the common depth point is vertically below the common midpoint. In the case of dipping beds, there is no common depth point shared by multiple sources and receivers, so dip moveout processing is necessary to reduce smearing, or inappropriate mixing, of the data. Alternate Form: common depth point

CDP

1. n. [Geology] A linear, commonly concave-based depression through which water and sediment flow and into which sediment can be deposited in distinctive, often elongated bodies. Channels can occur in a variety of morphologies, e.g., straight, meandering or braided. In some areas, coarse sediments can fill channels of streams or rivers that cut through finer grained sediments or rocks. The close proximity of coarse-grained and fine-grained sediments can ultimately lead to the formation of stratigraphic hydrocarbon traps. See: depositional environment,  point bar,  sediment,  stratigraphic trap,  trap,  turbidity current

channel

1. n. [Geophysics] A type of elastic wave propagated and confined in a layer whose velocity is lower than that of the surrounding layers, such as a layer of coal. See: surface wave

channel wave

1. n. [Geophysics] A distinguishing feature of a waveform in a seismic event, such as shape, frequency, phase or continuity. Alternate Form: signature See: frequency,  wave

character

1. n. [Geophysics] A type of borehole seismic data designed to measure the seismic traveltime from the surface to a known depth. P-wave velocity of the formations encountered in a wellbore can be measured directly by lowering a geophone to each formation of interest, sending out a source of energy from the surface of the Earth, and recording the resultant signal. The data can then be correlated to surface seismic data by correcting the sonic log and generating a synthetic seismogram to confirm or modify seismic interpretations. It differs from a vertical seismic profile in the number and density of receiver depths recorded; geophone positions may be widely and irregularly located in the wellbore, whereas a vertical seismic profile usually has numerous geophones positioned at closely and regularly spaced intervals in the wellbore. Synonyms: velocity survey,  well shoot See: correlate,  correlation,  depth conversion,  drift,  first break,  interpretation,  one-dimensional seismic data,  one-way time

checkshot survey

1. n. [Geophysics] A technique for acquiring full-azimuth (FAZ) marine seismic data. This technique uses a vessel equipped with source arrays and streamers to shoot and record seismic data; however, unlike conventional surveys acquired in a series of parallel straight lines, circle shooting surveys are acquired as the vessel steams in a series of overlapping, continuously linked circles, or coils. The circular shooting geometry acquires a full range of offset data across every azimuth to sample the subsurface geology in all directions. The resulting FAZ data are used to image complex geology, such as highly faulted strata, basalt, carbonate reefs, and subsalt formations. See: acquisition,  salt dome

circle shooting

1. n. [Geophysics] In multichannel seismic acquisition, the point on the surface halfway between the source and receiver that is shared by numerous source-receiver pairs. Such redundancy among source-receiver pairs enhances the quality of seismic data when the data are stacked. The common midpoint is vertically above the common depth point, or common reflection point. Common midpoint is not the same as common depth point, but the terms are often incorrectly used as synonyms. Alternate Form: common midpoint

CMP

1. n. [Geophysics] A measure of the similarity of two seismic traces. See: correlation,  phantom,  seismic trace,  semblance

coherence

1. n. [Geophysics] A technique for removing noise and emphasizing coherent events from multiple channels of seismic data. Alternate Form: coherent detection See: channel,  event,  filter

coherence filtering

1. adj. [Geophysics] Pertaining to seismic events that show continuity from trace to trace. Seismic processing to enhance recognition of coherent events and emphasize discontinuities such as faults and stratigraphic changes has gained popularity since the mid-1990s. See: coherence filtering,  discontinuity,  event,  fault,  random noise,  stratigraphy

coherent

1. n. [Geophysics] A technique for removing noise and emphasizing coherent events from multiple channels of seismic data. Synonyms: coherence filtering See: channel,  event,  filter

coherent detection

1. n. [Geophysics] Undesirable seismic energy that shows consistent phase from trace to trace, such as ground roll and multiples. See: air wave,  multiple reflection,  noise,  phase,  random noise

coherent noise

1. n. [Geophysics] In multichannel seismic acquisition where beds do not dip, the common reflection point at depth on a reflector, or the halfway point when a wave travels from a source to a reflector to a receiver. In the case of flat layers, the common depth point is vertically below the common midpoint. In the case of dipping beds, there is no common depth point shared by multiple sources and receivers, so dip moveout processing is necessary to reduce smearing, or inappropriate mixing, of the data. Alternate Form: CDP See: channel,  depth point,  dip,  fold,  stacking velocity

common depth point

1. n. [Geophysics] In multichannel seismic acquisition, the point on the surface halfway between the source and receiver that is shared by numerous source-receiver pairs. Such redundancy among source-receiver pairs enhances the quality of seismic data when the data are stacked. The common midpoint is vertically above the common depth point, or common reflection point. Common midpoint is not the same as common depth point, but the terms are often incorrectly used as synonyms. Alternate Form: CMP See: bins,  brute stack,  channel,  common midpoint method,  fold,  gather,  reflector,  stack,  velocity analysis

common midpoint

1. n. [Geophysics] Method of seismic reflection surveying and processing that exploits the redundancy of multiple fold to enhance data quality by reducing noise. During acquisition, an energy source is supplied to a number of shotpoints simultaneously. Once data have been recorded, the energy source is moved farther down the line of acquisition, but enough overlap is left that some of the reflection points are re-recorded with a different source-to-receiver offset. Multiple shotpoints that share a source-receiver midpoint are stacked. The number of times that a common midpoint is recorded is the fold of the data. See: processing,  shotpoint,  stack

common midpoint method

1. adj. [Geophysics] Pertaining to traces that have the same offset, or distance between source and receiver. See: trace

common offset