Tuesday 23 August 2005

G3
1000-1230 hours

132
Impact of GPS time series errors in the estimation of tectonic plate models
Bastos, Luísa¹, Bos, Machiel S¹, Fernandes, Rui M S^2,3,4, Combrink, Attie⁵
1 Astronomical Observatory - Faculty of Sciences of University of Porto, Portugal
2 Department of Informatics - University of Beira Interior, Covilhã, Portugal
3 Center of Geophysics of University of Lisbon, Portugal
4 Department of Earth Observation and Space systems, TU Delft, The Netherlands
5 Hartebeesthoek Radio Astronomy Observatory, Krugersdorp, South Africa
Author email: lcbastos@fc.up.pt
The correctness of the GPS uncertainties derived from estimation processes is a fundamental issue when these values are used as relative weights in further adjustments. Clearly, the formal uncertainties associated with best fit-line using position solutions are too optimistic because temporal correlation between observations is not taken into account. Many studies have shown recently that when this information is incorporated more realistic errors for the derived motions are obtained. As an example, we discuss the implications of the chosen noise model on the estimation of the angular velocities for the Nubia and Somalia tectonic plates using a network of continuously-operating GPS stations. This network contains all available stations on Africa, and it is processed on a daily basis (with a backward processing since 1996). We use three different noise models to estimate the angular velocities for the Nubia and Somalia plates: an empirical noise model, the white noise model, and the white + power law noise model. These three different noise models provide different weighting for each station in the angular velocity estimation, and therefore three different sets of values are obtained. We check which noise model produces an angular velocity that provides the best fit with the rigid plate assumption. In addition, for the Nubian plate, we perform an independent validation by comparing the motion residuals for a separate set of GPS stations in South Africa. We also show the effect of the three different noise models on the estimation of the Somalian angular velocity.

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