Normal Move Out
Encyclopedia
Normal Move Out is a term used in seismics
and geophysics
to describe the effect of the separation between receiver and source on the arrival time of a reflection that does not dip, abbreviated NMO. Filters and correcting algorithms must be used to properly image the subsurface.
In a land-based seismic survey blasts of dynamite or vibroseis units are used to create waves that will reflect off different layers of rock and are collected by equally spaced geophone
s or receivers placed along the surface. If a horizontal interface is present in the subsurface, seismic waves will reflect toward the surface recorded by geophones. Reflections from this surface will be received by the closest geophone first, arriving later at farther geophones. Because the wave must travel along the hypotenuse created between the depth of the event and source-receiver offset, the time delay increases hyperbolically
along equally spaced geophones. The hyperbolic distortion must be corrected in ordered to accurately image the subsurface.
Seismology
Seismology is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake effects, such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic,...
and geophysics
Geophysics
Geophysics is the physics of the Earth and its environment in space; also the study of the Earth using quantitative physical methods. The term geophysics sometimes refers only to the geological applications: Earth's shape; its gravitational and magnetic fields; its internal structure and...
to describe the effect of the separation between receiver and source on the arrival time of a reflection that does not dip, abbreviated NMO. Filters and correcting algorithms must be used to properly image the subsurface.
In a land-based seismic survey blasts of dynamite or vibroseis units are used to create waves that will reflect off different layers of rock and are collected by equally spaced geophone
Geophone
The term geophone derives from the Greek word "geo" meaning "earth" and "phone" meaning "sound".A geophone is a device which converts ground movement into voltage, which may be recorded at a recording station...
s or receivers placed along the surface. If a horizontal interface is present in the subsurface, seismic waves will reflect toward the surface recorded by geophones. Reflections from this surface will be received by the closest geophone first, arriving later at farther geophones. Because the wave must travel along the hypotenuse created between the depth of the event and source-receiver offset, the time delay increases hyperbolically
Hyperbola
In mathematics a hyperbola is a curve, specifically a smooth curve that lies in a plane, which can be defined either by its geometric properties or by the kinds of equations for which it is the solution set. A hyperbola has two pieces, called connected components or branches, which are mirror...
along equally spaced geophones. The hyperbolic distortion must be corrected in ordered to accurately image the subsurface.