37. If there are N geophones and the array moves forward a distance of nΔx between shots, it can be shown that the number of rays that share the same common midpoint is N/2n . This is the fold of the data. Fold is sometimes reported as a percentage of coverage (100×N/2n %) In the example below, there are 6 geophones and the array moves forward a distance of 1Δx between shots. This gives 3-fold CMP coverage or 300% coverage.
48. The synthetic seismogram in the fifth column was generated by convolving the digitized sonic and density logs with a wavelet shown in the column to the right. By comparing geological markers picked on logs, such as the top of the chalk in this display, with major reflections on the seismic section, seismic data can be used to map physical properties between wells.
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60. The crosslines of a 3D survey are perpendicular to the direction in which the data were acquired. The in-lines of a 3D survey are parallel to the direction in which the data were acquired, or in marine data, the direction in which the boat moves.
78. Obtaining four-component seismic data using a multiwave array system. Each sensor station within the cable comprises one hydrophone and three orthogonally oriented geophones to record both pressure and particle velocity.
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80. Unconformity A geological surface separating older from younger rocks and representing a gap in the geologic record. Such a surface might result from a hiatus in deposition of sediments, possibly in combination with erosion, or deformation such as faulting.
81. Angular Unconformity: A surface that separates younger strata from eroded, dipping, older strata and represents a gap in the geologic record.
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92. Fault plane is oriented between 30 and 90 degrees (measured from horizontal)
98. Pinch-out A type of stratigraphic trap. The termination by thinning or tapering out ("pinching out") of a reservoir against a nonporous sealing rock creates a favorable geometry to trap hydrocarbons, particularly if the adjacent sealing rock is a source rock such as a shale.