Quality factor is a measure of a particular type of energy loss (anelastic) that broadens and dampens seismic waves. It is one of many tools that can be used to examine the interior or the Earth. Quality factor decreases as temperature increases, which makes it useful for examining thermal anomalies. Quality factor also varies with chemical composition, pressure or stress, and volatile content. Consiquently it is not diagnostic on its own.

Seismic velocity (the velocity at which a seismic wave propagates through the earth) also varies with temperature, pressure, chemical composition, and volatile content. However, it varies in a distinctly different manner than quality factor.

Anisotropy occurs when a material behaves differently when observed from different directions. Seismic velocity may be anisotropic if the material propogates a wave at various velocities in various directions. This may occur as a result of latice prefered orientation (LPO) or shape prefered orientation (SPO). LPO often arrises when a mineral or mineral assemblage aligns in a direction due to strain from shear stress. SPO often arrises from layering of materials, so that the waves may travel faster along individual plane layers than through the bulk of the material.

Anisotropic quality factor is similar to anisotropic velocity. More or less energy loss may occur in one direction rather than another due to either SPO or LPO.

We inverted ~90,000 travel time and attenuation data for velocity and quality factor using differential methods (differencing the measurement of one wave from another). The models have identical resolution due to identical data. We calculated (vertical transverse) anisotropy from radial and tengential waveform. For more information, please examine chapter 6 of my thesis: Chapter 06

If you would like the model, please feal free to download it and have fun playing arround. VQM3DA.tar.gz

Vertical profiles throught our model, VQM3DA, show significant differences in both velocity and quality factor near subduction zones. The velocity and quality factor are both high beneath subduction zones and low beneath spreading ridges. The figure on the right shows velocity, quality factor anomaly, quality factor, and the resolution test. Click on the figure to the right to see a larger view (in PDF format).

Horizontal cross sections through our model demonstrate the similarities and differences between velocity and quality factor clearly. At shallow depths, the subduction zones posess low quality factor, while at greater depths due to high volitile content. At greater depths the quality factor increases beneath subduction zones. Cores of high velocity and quality factor may be seen around the Pacific. Click on the figure to the right to see a larger view (in PDF format).

Previous work by Gung and Romanowicz [2004] constrains upper mantle quality factor with surface waves. The resolution of their model, QRLW8, decreases with greater depth. Our model resolution decreases at shallower depths, where it begins to vertically smooth. The two models agree very well between 300 and 600 km depth. Click on the figure to the right to see a larger view (in PDF format).