See paragraph: "Seismic velocity is not a thermometer"

<http://www.mantleplumes.org/TomographyProblems.html>

By the way, I note the same confusion, i.e., denser material <=>higher
velocity:

"Nevertheless, tomographic images are often interpreted assuming that a
simple velocity-density-temperature correlation exists. High velocity
(blue) is generally attributed to cold, dense, sinking material, and low
velocity (red) as hot, low-density, rising material (Figures 4 & 5)."

Weird, isn't it?

Especially, that a few lines further:

"The African and south Pacific "superplumes" are vast, low-velocity
bodies in the lower mantle whose low velocities have been shown to
result from anomalously high density and not to high temperature
(Trampert et al., 2004)"

thus suggesting again that low velocities region are associated to high
density.

"Then seismology tells us that the velocity of both P and S waves
increases with depth in the mantle. Density also increases
with depth. So, if it was only for density the velocity of
seismic waves should decrease with depth. There is no other physically
possible way for seismic wave velocity to increase with depth but for
the elastic moduli to increase with depth at a faster rate than density.
This is impossible though if temperature increases with depth.
Experiment has shown that the elastic moduli are very sensitive to
temperature; rigidity decreases as temperature increases, and vice
versa, and at temperatures above 800 oC rigidity diminishes rapidly.
This decrease cannot in any way be compensated by pressure-depth,
because the pressure at any depth is below the rigidity and
incompressibility thresholds. For example according to the Preliminary
Reference Earth Model - PREM the density of crustal rocks at ~10 km
depth, is ~2900 kg/m3, the pressure ~0.3 GPa, whereas rigidity mu, and
incompressibility K, are ~26.6  and ~52 GPa, respectively. At 77 km the
density is ~3375 kg/m3, the static stress ~2.45 GPa, the rigidity ~67.4
GPa, and the incompressibility modulus ~130 GPa. At the depth of 667 km
the corresponding values for density rho, pressure, rigidity mu, and
incompressibility K are ~4381 kg/m3, ~23.8, ~155 and ~300 GPa, and at
2888 km they are ~5566 kg/m3, ~136, ~294, ~656 GPa."

"The implication is quite clear: Depth and therefore static
stress-pressure has no effect on elastic moduli. For seismic wave
velocity to increase with depth in the mantle rigidity has to increase
with depth; as a result temperature cannot increase with depth.
Therefore the seismic wave velocity profile is an approximation of the
actual, whereas the conventional temperature profile is not based on
observation, experiment and logic, i.e., it is not an approximation of
the actual."

So, where is the flaw?

[...]