Indoor seismology by probing the Earth's interior by using sound velocity measurements at high pressures and temperatures

Baosheng Li*,^† and
Robert C. Liebermann*,^‡

*Mineral Physics Institute and
^‡Department of Geosciences, Stony Brook University, Stony Brook, NY 11790

Edited by Russell J. Hemley, Carnegie Institution of Washington, Washington, DC, and approved March 12, 2007 (received for review October 2, 2006)

Abstract

The adiabatic bulk (K _S) and shear (G) moduli of mantle materials at high pressure and temperature can be obtained directly by measuring compressional and shear wave velocities in the laboratory with experimental techniques based on physical acoustics. We present the application of the current state-of-the-art experimental techniques by using ultrasonic interferometry in conjunction with synchrotron x radiation to study the elasticity of olivine and pyroxenes and their high-pressure phases. By using these updated thermoelasticity data for these phases, velocity and density profiles for a pyrolite model are constructed and compared with radial seismic models. We conclude that pyrolite provides an adequate explanation of the major seismic discontinuities at 410- and 660-km depths, the gradient in the transition zone, as well as the velocities in the lower mantle, if the uncertainties in the modeling and the variations in different seismic models are considered. The characteristics of the seismic scaling factors in response to thermal anomalies suggest that anticorrelations between bulk sound and shear wave velocities, as well as the large positive density anomalies observed in the lower mantle, cannot be explained fully without invoking chemical variations.

Footnotes

^†To whom correspondence should be addressed. E-mail: bli{at}notes.cc.sunysb.edu
Author contributions: B.L. and R.C.L. designed research; B.L. and R.C.L. performed research; B.L. and R.C.L. contributed new reagents/analytic tools; B.L. analyzed data; and B.L. and R.C.L. wrote the paper.
The authors declare no conflict of interest.
This article is a PNAS Direct Submission.
Abbreviations:

P wave,

compressional wave;

S wave,

shear wave;

ISS,

impulsive stimulated scattering;

RUS,

resonant ultrasound spectroscopy.