Other
Scientific paper
Dec 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003agufm.p12b1062p&link_type=abstract
American Geophysical Union, Fall Meeting 2003, abstract #P12B-1062
Other
5417 Gravitational Fields (1227), 5430 Interiors (8147), 5475 Tectonics (8149), 5494 Instruments And Techniques
Scientific paper
The goal of our effort is to find such an interior structure of Venus which best predicts the geoid data. Our models are based on different kinds of topography support. The predicted data are compared with observed ones on the basis of common spectral methods and localization methods. First, we apply the principle of isostasy and we look for an average apparent depth of compensation (ADC). For the whole spectrum, dominated by the low degrees, a 165 km depth is found which might correspond to a bottom of the lithosphere. However, the predicted geoid does not fit well to the observed data in the whole spectral interval. Studying the degree-dependent ADC and the admittance function we obtain a uniform depth of compensation around 35 km for degrees higher than 40. For the geoid at degrees lower than 40 we propose a dynamic origin. This hypothesis is investigated in the framework of the internal loading theory. Assuming that the buoyancy force does not vary with depth (which roughly corresponds to a plume-like style of mantle convection) we can well explain about 90% of both geoid and topography. The best fit to the data and the observed admittance function is found for the viscosity profile with a ~100 km thick lithosphere and a viscosity increase by factor 10-100 through the mantle. Second, we analyze our results by means of multiresolution methods. This technique is generally a useful tool for filtering the full-spectra signal. In comparison with the spherical harmonics the wavelet base (or some other suitable function) is well localized (i.e. has non-zero amplitudes only in a vicinity of the point of interest). So using this method we obtain true field anomalies without artificial oscillations. In our study of geoid and topography of Venus we can also look at localized "qualitative" fields: correlation and admittance. There are two major approaches - spectral one presented by Simons et al. (1997) and spatial one presented by Kido et al. (2003). We use the later one motivated by a possible improvement of resolution in the selected regions. For an intermediate and short wavelengths the spherical harmonic expansions of the geoid contain too much of global signature which makes the local features unreadable. In contrast, the use of a localization function gives us a clear picture with individual features. This could be a base for intuitive comparison of structures on the given scale - in our case observed and predicted fields. Localization of the qualitative functions as of correlation or admittance could give us information about observed geophysical models as well as about degree of agreement with our results and spatial errors. References: Kido, M., D.A. Yuen, and A.P. Vincent, Continuous wavelet-like filter for a spherical surface and its application to localized admittance function on Mars, Phys. Earth Planet. Inter., 135, 1-16, 2003. M. Simons, S. C. Solomon, and B. H. Hager, Localization of gravity and topography: Constraints on the tectonics and mantle dynamics of Venus,, Geophys. J. Int., 131, 24-44, 1997.
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