Editing Reflection seismology (section)

====Seismic data processing====
{{See also|Deconvolution|Seismic migration|Multidimensional seismic data processing}}
There are three main processes in seismic data processing: [[Deconvolution#Seismology|deconvolution]], [[common-midpoint]] (CMP) stacking and [[Seismic migration|migration]].<ref>{{Cite book| author=Yilmaz, Öz | year=2001 | title=Seismic data analysis | publisher=Society of Exploration Geophysicists | isbn=1-56080-094-1 |page= 4}}</ref>

''Deconvolution'' is a process that tries to extract the reflectivity series of the Earth, under the assumption that a seismic trace is just the reflectivity series of the Earth convolved with distorting filters.<ref>{{Cite book|first1=Robert |last1=E. Sheriff |first2=L. P. |last2=Geldart | year=1995 | title=Exploration Seismology |edition=2nd | publisher=Cambridge University Press | isbn=0-521-46826-4 |page= 292}}</ref>  This process improves temporal resolution by collapsing the seismic wavelet, but it is nonunique unless further information is available such as well logs, or further assumptions are made.  ''Deconvolution'' operations can be cascaded, with each individual deconvolution designed to remove a particular type of distortion.

''CMP stacking'' is a robust process that uses the fact that a particular location in the subsurface will have been sampled numerous times and at different offsets.  This allows a geophysicist to construct a group of traces with a range of offsets that all sample the same subsurface location, known as a ''Common Midpoint Gather''.<ref>{{cite web | website = [[Schlumberger]] Oifield Glossary | title = Common-midpoint | url = http://www.glossary.oilfield.slb.com/Display.cfm?Term=CMP | access-date = 8 September 2013 | archive-date = 31 May 2012 | archive-url = https://web.archive.org/web/20120531155223/http://www.glossary.oilfield.slb.com/Display.cfm?Term=CMP | url-status = dead }}</ref>  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|Normal moveout correction]]'' and ''statics correction''.  Unlike marine seismic data, land seismic data has to be corrected for the elevation differences between the shot and receiver locations.  This correction is in the form of a vertical time shift to a flat datum and is known as a ''statics correction'', but will need further correcting later in the processing sequence because the velocity of the near-surface is not accurately known.  This further correction is known as a ''residual statics correction.''

''Seismic migration'' is the process by which seismic events are geometrically re-located in either space or time to the location the event occurred in the subsurface rather than the location that it was recorded at the surface, thereby creating a more accurate image of the subsurface.