# Dictionary:Instantaneous q factor

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The instantaneous quality (Q) factor is a seismic attribute and is the ratio of instantaneous frequency to twice the instantaneous bandwidth.This Q computation is the short wavelength variation of the Q value, therefore, it gives relative values. [1]

${\displaystyle q(t)={\frac {-\pi Freq(s)}{decay(t)}}}$

Where ${\displaystyle decay(t)}$ is the instantaneous decay rate, which is defined as the first derivative of the trace envelope divided by the trace envelope envelop providing an expression:

${\displaystyle q(t)={\frac {-\pi Freq(s)E(s)}{\frac {dE(s)}{dt}}}}$

Where ${\displaystyle Freq(s)}$ is the instantaneous frequency while ${\displaystyle E(s)}$ is the trace envelope and ${\displaystyle {\frac {dE(s)}{dt}}}$ is the first derivative of the trace envelope.It is also a physical attribute with a strong relation to porosity, permeability, and fracture.

• Indicates local variation of Q factor, similar to the relative acoustic impedance computation from the seismic trace. Longer wavelength variation should be computed by spectral division and added to this attribute.
• May indicate liquid content by rationing pressure versus shear wave section Q factors.
• Indicates relative absorption characteristics of beds.
• It is a transmissive attribute; its various wavelength components should be estimated in a similar way to the average velocity and velocity inversion procedures.

## References

1. Taner, Turhan (1992), Attributes Revisited, Rock Solid Images Houston, Texas (published 2000)