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Thirty Years of Confusion around "Scattering Q"?

The past 30 years have seen vast advances in seismic instrumentation, computing infrastructure, and methodology. In particular, an impressive concept of the frequency-dependent attenuation quality, Q(f), was created, followed by a dazzling array of related theories and models. However, revisiting some of its original postulates still shows that theoretical models may have run somewhat ahead of the observational constraints. Many presentations of Q(f) have been influenced by the prevalence of particular models, especially those based on random scattering. This led to the well-known apparent character of Q(f) and excessive complexity of its interpretations, which start from unrealistic assumptions about the wavefield and then justify them in retrospect. To regain clarity, I suggest abandoning the use of Q for scattering and reviewing some of the key datasets in an assumption-free and data-driven manner. Initial efforts in this direction show that frequency-dependent Q may not be nearly as widespread as currently thought. These points are briefly discussed below.

From discussions with many seismologists, I discovered that it is surprisingly difficult to argue these simple points. The problem seems rooted in the established culture of corroborating models by other models and other authors' papers, and in a sacred belief in the magic of algorithms and less attention to the data.

 

	Current Q(f) Paradigm—Inadequate for Structured Earth

 
In most interpretations of seismic attenuation, the measurements can be reduced to inversion of some time- and frequency-variant path factor P(t, f) representing the seismic amplitudes from which the effects of the source and receiver have been removed:

(1)

A well-known fundamental problem is the definition of the geometrical spreading factor, G₀(t), which in some cases may also be frequency-dependent. When G₀(t) is set from simple theoretical considerations (e.g., G₀(t) t^–1 for . . . [Full Text of this Article]

Igor B. Morozov

Department of Geological Sciences
University of Saskatchewan
Saskatoon, Saskatchewan S7N 5E2 Canada
igor.morozov@usask.ca

This article has been cited by other articles:

				J. Xie and M. Fehler Comment on "Thirty Years of Confusion around `Scattering Q'?" by Igor B. Morozov Seismological Research Letters, July 1, 2009; 80(4): 646 - 647. [Full Text] [PDF]

				I. B. Morozov Reply to "Comment on `Thirty Years of Confusion around `Scattering Q'?'" by J. Xie and M. Fehler Seismological Research Letters, July 1, 2009; 80(4): 648 - 649. [Full Text] [PDF]