Elasticity of Rocks at High Temperatures with Special : Reference to the Nature of the Low Velocity Layer in the Crust and the Upper Mantle of the Earth

Abstract

In this article, historical review of the experimental approach to the thermal dependence of elasticity of rocks and other broad characters of the subject matter are omitted. In general, change of elastic constants with temperature for single crystal and polycrystalline aggregate is different, and it is discussed by Ke’s model with grain boundary viscosity. Accordingly, it is impossible or at least very difficult to estimate the elastic parameters of polycrystalline aggregate at various temperatures, especially at high temperatures, based on the experimental values for the constituent single crystals. As for the low velocity layer in the earth’s crust proposed by Gutenberg, Hughes’ opinion that it is due to the preponderance of the velocity decrease by temperature is examined. Poisson’s ratio, calculated from Hughes’ measurements of V_p and V_s, shows the irregular change with temperature and pressure. It was concluded that the low velocity layer in the crust is not due to the effect of temperature, but due to the predomination of rocks having higher velocities in the upper crust. Low velocity zone in the upper mantle was examined from the behavior of Poisson’s ratio as a function of temperature adopting the materials of Gutenberg’s model. It was shown that there is some possibility to estimate the temperature distribution or the temperature gradient in the upper mantle by means of the comparison of the variation of Poisson’s ratio with depth in the earth to that with temperature. It is due to the fact that Poisson’s ratio is scarcely affected by pressure. Temperature distribution was drawn with rough assumption, and it seems interesting to see that temperature gradient becomes extraordinarily large at the upper part of the low velocity zone.