Evidence for a ubiquitous seismic discontinuity at the base of the mantle
A sharp discontinuity at the base of Earth's mantle has been suggested from seismic waveform studies; the observed travel time and amplitude variations have been interpreted as changes in the depth of a spatially intermittent discontinuity. Most of the observed variations in travel times and the spatial intermittance of the seismic triplication can be reproduced by a ubiquitous first-order discontinuity superimposed on global seismic velocity structure derived from tomography. The observations can be modeled by a solid-solid phase transition that has a 200-kilometer elevation above the core-mantle boundary under adiabatic temperatures and a Clapeyron slope of about 6 megapascal per kelvin.
Sidorin
I
Seismological Laboratory 252-21, California Institute of Technology, Pasadena, CA 91125, USA.
Gurnis
M
Helmberger
DV