Measuring contemporary deformation in the Taupo Volcanic Zone, New Zealand using SAR interferometry
Jessica Hole(1) , Andrew J. Hooper(2)
, Nicola F. Stevens(3)
, and Geoff Wadge(1)
ESSC, University of Reading,
Harry Pitt Building,
RG6 6AL, Reading,
(2) Stanford University, Ruth Wattis Mitchell Earth Sciences Bldg, Stanford, California 94305, United States
(3) Institute of Geological and Nuclear Sciences, 69 Gracefield Road, Lower Hutt, New Zealand
The Taupo Volcanic Zone (TVZ) is an area of active back-arc extension in the North Island, New Zealand, that represents the most productive area of rhyolitic volcanism on earth. The relationship between the magmatism and active rifting has produced a complex system where it is hard to distinguish between cause and effect, and how tectonic and volcanic deformation signals are distributed across the TVZ. At present, deformation in the TVZ is measured by differential GPS on 2-3 yearly campaign visits and at widely spaced continuous stations. Campaign GPS has shown that the TVZ is widening by 8mm/yr (Darby and Meertens,1995) but so far the network has been too sparse to identify how the extension is distributed and a number of benchmarks are known to be affected by geothermal subsidence. In this paper we investigate the use of C-band interferometry for the measurement of TVZ deformation. Archived descending-pass ERS SAR images are available from 1996-2003 and ascending and descending Envisat ASAR images have been collected since 2003 with two different look angles to suit the different styles of deformation. We have shown that C-band can be used to measure contemporary deformation in the TVZ but that extracting tectonic information is difficult due to large temporal decorrelation in the interferograms. Using short-term, low baseline pairs, it is possible to map the extent of geothermal subsidence at high resolution, which can be combined with model of the expected deformation produced by interpolation of differential GPS measurements (Beavan and Haines, 2001). This can be used to improve the unwrapping of longer-term pairs that have reduced coherence, which must be considered in order to measure the 8mm/yr horizontal deformation signal. The lack of interferogram coherence in the TVZ, and the subsequent difficulty in phase unwrapping and orbital error correction can also be overcome by using persistent scatter or other multi-temporal InSAR techniques. Using the technique of Hooper (2004), we have identified a longer wavelength signal in the central TVZ, which could be of tectonic or magmatic origin.
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