Anelastic attenuation factor: Difference between revisions

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In [[reflection seismology]], the '''anelastic attenuation factor''', often expressed asor '''seismic quality factor''', oroften expressed as the '''Q factor''' (whichwhere ishigher inverselyQ proportionalmeans toless attenuationenergy factorloss), quantifiesmeasures thehow effects[[Seismic ofwave|seismic waves]] weaken due to anelastic [[attenuation]]—the onloss the [[seismicof wave]]let energy that eventually ends up as heat, caused by fluid movement and grainfriction boundarywithin frictionthe Earth’s subsurface. As a seismic wave propagatestravels through a medium, thelike [[elasticrock, wave|elastic]]this energy associated with the wave isabsorption gradually absorbedreduces byits the medium, eventually ending up as [[heat energy]]. This is known as [[Absorption (electromagnetic radiation)|absorption]] (or anelastic attenuation)strength and willcan eventually causemake theit totaldisappear disappearance of the seismic wavecompletely.<ref>Toksoz, W.M., & Johnston, D.H. 1981. Seismic Wave Attenuation. SEG.</ref> The Q factor helps geophysicists understand these effects on seismic signals, aiding in the study of underground structures.

==Quality factor, ''Q''==

''Q'' is defined as

:<math>Q = 2{\pi}\left ( \frac{E}{{\delta}E} \right )</math>

where <math>\frac{{\delta}E}{E}</math> is the fraction of energy lost per cycle.<ref>Sheriff, R. E., Geldart, L. P., (1995), 2nd Edition. ''Exploration Seismology''. Cambridge University Press.</ref>

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==Measurement of Q==

===Spectral ratio method===
<ref>Tonn, R. 1991. The determination of seismic quality factors Q from VSP data: A comparison of different computational methods. ''Geophys. Prosp.'' 39, 1-27.</ref>===

The geometry of a zero-offset vertical seismic profile (VSP) makes it an ideal survey to use for the calculation of Q using the spectral ratio method. This is because of the coincident raypaths that traverse a given rock layer, ensuring that the only path difference between two reflected waves (one from the top of the interval and one from the bottom) is the interval of interest. Stacked surface [[seismic reflection]] traces would offer similar signal-to-noise ratio over a much larger area but cannot be used with this method because every sample represents a different raypath and therefore will have experienced different attenuation effects.<ref>Dasgupta, R., & Clark, R.A. (1998) Estimation of Q from surface seismic reflection data. ''Geophysics'', '''63''', 2120-2128</ref>

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* [[Acoustic attenuation]]

* [[Attenuation]]

* [[Q models (seismology)]]

* [[Kolsky Q models]]

* [[Azimi Q models]]

==References==