Tuesday 23 August 2005

G3

PT0057
Measuring mountain uplift using continuous GPS
Denys, Paul¹, Beavan, John², Hager, Brad³, Molnar, Peter⁴, Herring, Tom³,
1 Otago University, New Zealand
2 Institute of Geological and Nuclear Sciences, New Zealand
3 Massachusetts Institute of Technology, USA
4 University of Colorado at Boulder, USA
Author email: pdenys@stonebow.otago.ac.nz
The Southern Alps in New Zealand have been formed through convergence normal to the Alpine fault over the past 6-7Ma. Although most of the deformation is associated with the horizontal component, we have attempted to measure accurately the vertical component using continuous GPS (CGPS) from a network of 12 sites along a profile between Westland and Mt Cook. The vertical measurements enable us to quantify the uplift rates as well as how the deformation varies between the Alpine Fault and the Main Divide. This provides a better understanding of how the Southern Alps came to be, and how they will evolve in the future. We now have five years of data observed in a harsh environment where the main technological challenge has been maintaining the equipment in environmental conditions that includes significant snow and ice, high winds and 9 metres of rainfall per annum. The maximum uplift rates are occurring between the Alpine fault and the Main Divide (~3000metres), but there are also significant periodic variations including seasonally induced annual and semi-annual terms in the site positions. These seasonal variations are mostly likely to be caused by a combination of thermo-elastic response of the rock, snow and ice loading and ground water loading that is affected by the rock porosity. Seasonal variations may also potentially be caused by local environment or instrument induced errors such as antenna thermal noise or phase centre variations, multipath or inadequacies in atmospheric models. The benefits of investigating unmodeled and mismodeled seasonal errors provides insight into seasonal deformation caused by tectonic or other geophysical processes as well as characterising the GPS error spectrum on seasonal scales.

Return to Poster Presentations