Equations of State of the Earth

The major results of research in the United States for 1971-1974 in the areas of static, high-pressure X ray, ultrasonic and shock wave measurements, and progress in theoretical equations of state are summarized. This 4-year period has seen the massive accumulation of new data pertinent to describing the properties, and to some extent geodynamic processes, of the upper mantle as well as exposing the gauntlet of scientific challenge with regard to our lack of detailed understanding of the major changes in crustal seismic velocities, which seem to offer so much promise for earthquake prediction. In the area of very high pressure geophysics, another challenging problem uncovered is the question of explaining the low adiabatic gradient in the outer core, which seems to be required to retain liquid iron alloy material at the melting point. Important advances in what until recently has been quite empirical elastic moduli 'systematics' have demonstrated how ionic radii and ionic packing densities may be quantitatively employed to predict unmeasured equations of state as well as tie together an ever increasing body of data for the elasticity of compounds which are crystal-chemical analogs of mantle minerals. The lack of suitable pure and mechanically homogeneous samples has continued to offer a serious obstacle to the study of candidate materials of the earth's interior. When samples of critically important minerals have been synthesized in such laboratories as those of A. E. Ringwood and R. Liebermann (Canberra) and S. Akimoto (Tokyo), significant new experiments and, shortly thereafter, theoretical results have been forthcoming. Several scientific meetings and meeting proceedings published in the years 1971-1974 have included contributions from the United States and have focused on the presentation of new data and theoretical interpretations. Two symposia of the International Association of Seismologists and Physics of the Earth's Interior (IASPEI) were organized at the fifteenth meeting of the IUGG: The State of Substance in the Earth's Interior (V. A. Magnitsky, Convener) and the Final Report, Upper Mantle Project (V. V. Beloussov, Chairman). Most of the papers presented at these two symposia are published in special issues of Physics of the Earth and Planetary Interiors (volume 5, pp. 267-343) and Tectonophysics (volume 13, pp. 1-644). The latter group of papers has also been published separately as a book [Ritsema, 1972]. The scientific reports of the Upper Mantle Project Symposium on Mechanical Properties and Processes of the Upper Mantle (Orson L. Anderson and L. R. Sykes, Conveners) held in Flagstaff, Arizona, in 1970 are published as a group in the Journal of Geophysical Research (volume 76(5), 1971). The proceedings of a conference held in Cambridge, Massachusetts, in April 1970 honoring Francis Birch, published in 1972 [Robertson, 1972], contains several articles dealing with equations of state. The proceedings of a special conference, convened by S. K. Runcorn, held at the Lunar Science Institute in March 1972, Copyright © 1975 by the American Geophysical Union. entitled Conference on High Pressure Physics and Planetary Interiors, was published in Physics of the Earth and Planetary Interiors (volume 6, pp. 1-209) and was also separately reprinted as a book [Runcorn, 1972]. At the IASPEI meeting in Lima, Peru, in August 1973, a symposium entitled The State and Behavior of Material Inside the Earth was convened by O. Anderson. Papers presented at this symposium were published individually. Numerous U.S. contributions to the NATO Institute on Petrophysics (S. K. Runcorn, Convener) held in Newcastle, U.K., on March 25-29, 1974, and the Fourth International Conference on High Pressure, on November 25-29, 1974, held in Kyoto, Japan (J. Osugi, Kyoto University, Chairman), are to be published. A major trend in the use of the international meter kilogram second system of units has started in the United States. During the last 2 years, several laboratories largely associated with the Atomic Energy Commission, now Energy Research and Development Agency, have begun to report pressures in N/m:, i.e., pascals. Thus 1 Mpa = 108 N/m:= 10 bars = 107 dyn/cm:.