Elastic thickness estimates for venus using line of sight accelerations from Magellan cycle 5

The elastic thickness, T-e, for various regions of Venus is estimated by co mparing the observed line of sight (LOS) acceleration of the Magellan space craft 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 par ticular, the topographic highs associated with Beta, Phoebe, Bell, and Eist la are thought to be dynamically supported. At shorter wavelengths, the adm ittance 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 crusta l thickness of 16 km and a density of 2670 kg m(-3). The observed variation s in admittance between different regions are unlikely to be due to differe nces in crustal thickness or density, and probably represent real variation s in T-e. The values obtained are similar to those from an identical analys is using cycle 4 data. Estimates of the elastic thickness of the Ovda and A lpha regions are unreliable, probably because the topography is not well de termined. No reliable estimates of elastic thickness could be made from cyc le 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. (C) 2000 Academic Press.