The high-temperature acoustic Grüneisen parameter in the earth's interior

The value of the acoustic Grüneisen parameter, γ_a, in the earth's interior has been computed using data from recent models obtained by inversion of normal data. In this paper we emphasize the data from the PEM model of the earth because there has been sufficient smoothing of the seismic data so that the derivatives d ln ν_s/d ? and d ln ν_p/d ? can be well defined at all depths.The results for the lower mantle show that γ_a decreases exponentially from 1.3 to 1.0, and there are several consistent cross-checks of the limiting values. We find γ_a is about 1.5 for the inner core and outer core. These results confirm, in broad outline, the results of others who computed γ for the core by entirely different methods. They also confirm a higher value of γ in the inner core. The value of γ_a in the lower mantle follows a ρ^?1.35 law, which is reminiscent of the expirical law γρ = constant, commonly used in shock-wave analyses.