Physics
Scientific paper
Dec 1994
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1994georl..21.2613h&link_type=abstract
Geophysical Research Letters (ISSN 0094-8276), vol. 21, no. 24, p. 2613-2616
Physics
32
Discontinuity, Earth Mantle, Phase Transformations, Seismic Waves, Seismology, Depth, Olivine, Temperature Dependence, Thermodynamics
Scientific paper
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 to 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(prime sub 410) P(prime) 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 to 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.
Bina Craig R.
Helffrich George
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