Q of the Earth

Abstract

Regional body wave and surface wave studies indicate that there is a low-Q upper mantle layer underlying a high-Q lithosphere. Great circle surface wave attenuation is used to refine the Q structure of the upper mantle and to demonstrate that these features are consistent with the global data. Body wave results are used to constrain the average Q of various regions of the mantle and core and the Q gradient in the lower mantle. Normal mode data are used to test the hypotheses that bulk dissipation is not required in the mantle and that the inner core has low Q. Both hypotheses are consistent with the data. The data are also consistent with a smooth increase of Q with depth over most of the lower mantle and a low-Q zone at the base of the mantle. The radial modes require bulk dissipation somewhere in the earth, probably in the inner core. A series of parametric models is presented which illustrate the sensitivity of the attenuation data to major features of the Q distribution.