What is NMO velocity?
NMO, or normal moveout, is the difference between the zero offset travel time and the travel time observed for a given source-receiver offset in a surface seismic survey. Offset traces must be corrected for normal moveout to correctly position the reflection in time.
Why NMO correction is done?
The velocity field (Figure 1.5-12) is used in normal moveout (NMO) correction of CMP gathers. Based on the assumption that, in a CMP gather, reflection traveltimes as a function of offset follow hyperbolic trajectories, the process of NMO correction removes the moveout effect on traveltimes.
What is normal moveout in seismic?
1. n. [Geophysics] The effect of the separation between receiver and source on the arrival time of a reflection that does not dip, abbreviated NMO. A reflection typically arrives first at the receiver nearest the source.
What is NMO stretch?
As a result of the NMO correction, a frequency distortion occurs, particularly for shallow events and at large offsets. This is called NMO stretching and is illustrated in Figure 3.1-10. The waveform with a dominant period T is stretched so that its period T0, after NMO correction, is greater than T.
How do you test for NMO?
Your doctor might be able to detect lesions or damaged areas in your brain, optic nerves or spinal cord. Blood tests. Your doctor might test your blood for the autoantibody NMO -IgG, which helps doctors distinguish NMO from MS and other neurological conditions. This test helps doctors make an early diagnosis of NMO .
What is the difference between MS and NMO?
In MS, individual episodes are usually mild; their cumulative effect over time may or not not cause progressive disability. In NMO, the opposite is true and therefore early diagnosis is critical; acute episodes are usually severe and – if untreated – can have devastating, irreversible effects on function.
What is normal moveout correction in geophysics?
A function of time and offset that can be used in seismic processing to compensate for the effects of normal moveout, or the delay in reflection arrival times when geophones and shotpoints are offset from each other.
What is normal moveout in geophysics?
The effect of the separation between receiver and source on the arrival time of a reflection that does not dip, abbreviated NMO. A reflection typically arrives first at the receiver nearest the source.
How does dip angle affect NMO velocity for a dipping reflector?
This equation indicates that proper stacking of a dipping event requires a velocity that is greater than the velocity of the medium above the reflector. In conclusion, the NMO velocity for a dipping reflector depends on the dip angle. The larger the dip angle, the higher the moveout velocity, hence the smaller the moveout.
How do you calculate the normal moveout of a reflector?
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. 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}}}}.
What is the NMO equation for normal moveout?
The NMO equation defines the normal moveout function. The total reflection (or offset) time tr is given by the NMO (or zero-offset) time tn, the offset x and the velocity of the medium V : where, for an apparent depth d to a zero-dipping reflector in the subsurface,
What is the traveltime equation for a horizontal reflector?
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.