Theory
Tomography is solved as an inverse problem. First measurements are made of seismic waves passing through a material. The character of these measurements is then analyzed to make inferences on the material such waves have passed through (velocity, density, etc.). The velocity of p and s waves depends on the rheology of the material that they travel through (density and elasticity). In short, variations in chemical compositions and thermal structure result in a change of velocity. Such waves can travel faster through relatively colder material. It is observed that wave velocity increases with increasing depth from 2–8 km/s in the crust up to 13 km/s in the mantle. Current research is based on this premise.
Read more about this topic: Seismic Tomography
Famous quotes containing the word theory:
“The theory of rights enables us to rise and overthrow obstacles, but not to found a strong and lasting accord between all the elements which compose the nation.”
—Giuseppe Mazzini (1805–1872)
“The great tragedy of science—the slaying of a beautiful theory by an ugly fact.”
—Thomas Henry Huxley (1825–1895)
“every subjective phenomenon is essentially connected with a single point of view, and it seems inevitable that an objective, physical theory will abandon that point of view.”
—Thomas Nagel (b. 1938)