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In geophysics and reflection seismology, amplitude versus offset (AVO) or amplitude variation with offset is the general term for referring to the dependency of the seismic attribute, amplitude, with the distance between the source and receiver (the offset).
Seismic data is sorted by common midpoint and then corrected for normal moveout. In reflection seismology, normal moveout (NMO) describes the effect that the distance between a seismic source and a receiver (the offset) has on the arrival time of a reflection in the form of an increase of time with offset. [1]
Examples of seismic attributes can include measured time, amplitude, frequency and attenuation, in addition to combinations of these. Most seismic attributes are post-stack, but those that use CMP gathers, such as amplitude versus offset (AVO), must be analysed pre-stack. [2]
The average amplitude is then calculated along a time sample, resulting in significantly lowering the random noise but also losing all valuable information about the relationship between seismic amplitude and offset. Less significant processes that are applied shortly before the CMP stack are Normal moveout correction and statics correction ...
Drill-noise VSPs (F), also known as seismic-while-drilling (SWD) VSPs, use the noise of the drill bit as the source and receivers laid out along the ground. Multi-offset VSPs (G) involve a source some distance from numerous receivers in the wellbore. [1] [2] A vertical seismic profile is constructed to identify a value known as a source wavelet.
Seismic migration is the process by which seismic events are geometrically re-located in either ... Zero-offset data is important to a geophysicist because the ...
Simultaneous Inversion (SI) is a pre-stack method that uses multiple offset or angle seismic sub-stacks and their associated wavelets as input; it generates P-impedance, S-impedance and density as outputs (although the density output resolution is rarely as high as the impedances). This helps improve discrimination between lithology, porosity ...
The offset range used depends on the depth of the target. For the top few kilometres of the crust, such as when investigating beneath a thick layer of basalt , a range of 10–20 km may be appropriate, while for the lower crust and mantle, offsets greater than 100 km are normally necessary.