Publication Abstract [View Article (PDF)]

Helffrich, G., and C. R. Bina, Frequency dependence of the visibility and depths of mantle seismic discontinuities, Geophysical Research Letters, 21, 2613-2616, doi:10.1029/94gl02341, 1994.

Abstract. The visibility and apparent position of a seismic gradient zone depends on the seismic wave frequency at which it is observed, which we illustrate by showing how the visibility and depth of the olivine alpha -> beta phase transformation (410 km discontinuity) change as temperature varies. Temperature variations change bottomside reflection coefficients by factors of 2-4 in the 0.5-1.0 Hz frequency band, which can explain spatial variability in short period P´410P´ observations and the small apparent variability in observed 410 km discontinuity depths. Discontinuity depths inferred from the time lags of these reflections are also frequency dependent, leading to a frequency dependence of estimates of mantle lateral thermal variability based on discontinuity displacements. The frequency dependent seismic Clapeyron slopes for the olivine alpha -> beta phase change we compute are 2.04 MPa/K at 0.2 Hz and 2.12 MPa/K at 0.05 Hz, and differ significantly from thermodynamic slope for the Mg2SiO4 end-member.

Copyright © 1994 American Geophysical Union
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Copyright © 1995 Craig R. Bina.