Elastic thickness estimates for Venus using line of sight accelerations
from Magellan cycle 5
D. Barnett, F. Nimmo and D. McKenzie Icarus 146, 404-419, 2000. PDF file (810K) available)
The elastic thickness, Te, for various regions of Venus is estimated by
comparing the observed line of sight (LOS) acceleration of the Magellan
spacecraft with that predicted using a spherical harmonic representation
of the topography, to degree and order 360. At long wavelengths (typically
longer than about 500 km) the transfer function between the topography and
gravity, or admittance, usually has a flat spectrum with a magnitude of
between 20 and 50 mgal km-1, which is most likely due to convective
support. In particular, the topographic highs associated with Beta,
Phoebe, Bell and Eistla are thought to be dynamically supported. At
shorter wavelengths, the admittance increases, suggesting a component of
flexural support. The elastic thicknesses are constrained by fitting
theoretical admittance curves to the observed short wavelength values for
the admittance. Results from Magellan cycle 5 show evidence of regional
variations in elastic thickness between about 19 and 29 km, with a mean
value of around 21-23 km, assuming a crustal thickness of 16 km and a
density of 2670 kg m-3. The observed variations in admittance between
different regions are unlikely to be due to differences in crustal
thickness or density, and probably represent real variations in Te. The
values obtained are similar to those from an identical analysis using
cycle 4 data. Estimates of the elastic thickness of the Ovda and Alpha
regions are unreliable, probably because the topography is not
well-determined. No reliable estimates of elastic thickness could be made
from cycle 6 data where the altitude of the spacecraft was higher than
about 300 km, due to the reduction in short wavelength signal amplitude
with altitude.
Francis' Page
Department of Earth Sciences
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nimmo@esc.cam.ac.uk
This page was last modified on 22 May 2000.