A geodetic measurement of strain variation across the central southern Alps, New Zealand

Abstract

An analysis of both continuous and campaign GPS data has been used to determine the degree of strain rate variability that is occurring, due to tectonic deformation, from two GPS networks that cross the Alpine Fault and the Main divide in the central Southern Alps, New Zealand. The campaign GPS data was observed during four regional campaigns covering an eight year period between 1994 and 2002, while a network of permanently tracking receivers has collected data over a 5.5 year period. Both data sets enable the estimation of high precision horizontal velocities that measure the velocity variation and hence crustal deformation that is occurring across the region. The permanently tracking receivers clearly show significant localised site displacements that appear to be caused or induced by seasonal changes in the environmental conditions. Such site dependant localised displacements exceed 1 cm at several sites and demonstrates the highly dynamic nature of the Southern Alps. In general, the long term strain rates determined from the permanently tracking network and the regional strain rates are in agreement, but there does appear to be evidence of variation in strain on a regional scale. In particular, there is evidence for a zone of extension even though the Alpine Fault is an oblique thrust fault caused by convergence across the plate boundary zone. © Springer-Verlag Berlin Heidelberg 2007.