Q of the Earth

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 attentuation 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 attentuation data to major features of the Q distribution.