The relative density-to-shear velocity scaling in the uppermost mantle

Details The relative density-to-shear velocity scaling in the uppermost mantle The relative density-to-shear velocity scaling in the uppermost mantle

Aug 2001

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2001pepi..124..193d&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 124, Issue 3-4, p. 193-212.

Physics

17

Scientific paper

We perform inversions of gravity data (geopotential model EGM96) and seismic tomography model (S16RLBM) for the scaling factor (ζ), which relates relative density anomalies to relative S-wave velocity anomalies. The gravity data and tomographic model are anti-correlated below continents down to a depth of /z=200km. This anti-correlation is not present below oceans. Except for smoothness, which is controlled by a damping factor, no a priori information is added to the inversion. Data are filtered between degrees /l=11 and /l=16 of the spherical harmonic expansion. This spectral window is well suited for the study of intermediate-size (2000-4000km) anomalies in the uppermost mantle. Calculations are made separately for sub-continental and sub-oceanic mantle. The sub-continental and sub-oceanic scaling factors are significantly different at depths shallower than 260km. In both cases, the magnitude of ζ is around 0.05. The sub-continental scaling factor has a positive root down to /z=220km, whereas the sub-oceanic scaling factor yields positive values down to /z=140km only. At depth shallower than 350km, models of ζ do not depend on the damping factor or the viscosity model. At depths greater than 350km, the resolution of ζ(z) decreases significantly and low degrees (/l=2-4) add information from large-scale anomalies and from the lower mantle. As a result, the shape and values of ζ for /l=2-16 and /l=11-16 are significantly different at depths greater than 350km. A possible explanation of the discrepancies between the sub-continental and sub-oceanic scaling factor is that intermediate-scale anomalies are more important in the continental uppermost mantle than in the oceanic uppermost mantle.

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