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] The relationship between arrival time and offset is hyperbolic and it is the principal criterion that a geophysicist uses to decide whether an event is a reflection or not.[2] It is distinguished from dip moveout (DMO), the systematic change in arrival time due to a dipping layer.
Seismic data is sorted by common midpoint and then corrected for normal moveout
The normal moveout depends on complex combination of factors including the velocity above the reflector, offset, dip of the reflector and the source receiver azimuth in relation to the dip of the reflector.[3] For a flat, horizontal reflector, the traveltime equation is:
where x = offset; v = velocity of the medium above the reflecting interface; = travel time at zero offset, when the source and receiver are in the same place.[4]
According to W. Harry Mayne, inventor of the Common Point Reflection Method in 1950, in order to avoid the "smearing" of recorded seismic data caused by the use of geophonesensor arrays, I needed a very long array to attenuate the noise, yet each point of the array needed to represent the same reflection point of the subsurface. For a non-dipping reflector, this meant that the source and receiver station would have to move the same distance-in opposite directions-from the reflection (or mid-) point. One problem still remained. The reflections had different traveltimes on each pair of sources and receivers, so it would be necessary to correct for these differences (moveouts) prior to array formation." Coupled with the normal moveout correction, Mayne stated, "the method was primarily intended to attenuate systematic surface noise, and to average out near-surface aberrations in travel paths. It was soon realized, however, that it alone could also substantially attenuate the insidious multiple reflection."[5]
^Sheriff, R. E., Geldart, L. P. (1995). Exploration Seismology (2nd ed.). Cambridge University Press. p. 86. ISBN0-521-46826-4.{{cite book}}: CS1 maint: multiple names: authors list (link)
^Yilmaz, Öz (2001). Seismic data analysis. Society of Exploration Geophysicists. p. 274. ISBN1-56080-094-1.
^Green, C.H. (1938). "Velocity determination by means of reflection profiles". Geophysics. Society of Exploration Geophysicists. 3 (4): 295–305. Bibcode:1938Geop....3..295G. doi:10.1190/1.1439508.
^Mayne, W. Harry (1989). 50 Years of Geophysical Ideas. Tulsa: Society of Exploration Geophysicists. pp. 93–96. ISBN0931830737.
March 17, 2024
normal, moveout, reflection, seismology, normal, moveout, describes, effect, that, distance, between, seismic, source, receiver, offset, arrival, time, reflection, form, increase, time, with, offset, relationship, between, arrival, time, offset, hyperbolic, pr. 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 The relationship between arrival time and offset is hyperbolic and it is the principal criterion that a geophysicist uses to decide whether an event is a reflection or not 2 It is distinguished from dip moveout DMO the systematic change in arrival time due to a dipping layer Seismic data is sorted by common midpoint and then corrected for normal moveoutThe normal moveout depends on complex combination of factors including the velocity above the reflector offset dip of the reflector and the source receiver azimuth in relation to the dip of the reflector 3 For a flat horizontal reflector the traveltime equation is t 2 t 0 2 x 2 v 2 displaystyle t 2 t 0 2 frac x 2 v 2 where x offset v velocity of the medium above the reflecting interface t 0 displaystyle t 0 travel time at zero offset when the source and receiver are in the same place 4 According to W Harry Mayne inventor of the Common Point Reflection Method in 1950 in order to avoid the smearing of recorded seismic data caused by the use of geophone sensor arrays I needed a very long array to attenuate the noise yet each point of the array needed to represent the same reflection point of the subsurface For a non dipping reflector this meant that the source and receiver station would have to move the same distance in opposite directions from the reflection or mid point One problem still remained The reflections had different traveltimes on each pair of sources and receivers so it would be necessary to correct for these differences moveouts prior to array formation Coupled with the normal moveout correction Mayne stated the method was primarily intended to attenuate systematic surface noise and to average out near surface aberrations in travel paths It was soon realized however that it alone could also substantially attenuate the insidious multiple reflection 5 References edit Schlumberger Oilfield Glossary NMO Sheriff R E Geldart L P 1995 Exploration Seismology 2nd ed Cambridge University Press p 86 ISBN 0 521 46826 4 a href Template Cite book html title Template Cite book cite book a CS1 maint multiple names authors list link Yilmaz Oz 2001 Seismic data analysis Society of Exploration Geophysicists p 274 ISBN 1 56080 094 1 Green C H 1938 Velocity determination by means of reflection profiles Geophysics Society of Exploration Geophysicists 3 4 295 305 Bibcode 1938Geop 3 295G doi 10 1190 1 1439508 Mayne W Harry 1989 50 Years of Geophysical Ideas Tulsa Society of Exploration Geophysicists pp 93 96 ISBN 0931830737 Retrieved from https en wikipedia org w index php title Normal moveout amp oldid 1144767337, wikipedia, wiki, book, books, library,
