Deformations occurring in the city of Auckland, New Zealand as mapped by the differential synthetic aperture radar

Auckland is the largest city in New Zealand with a current population of more than one million. It is situated on a basaltic volcanic field with a total area of 360 square km and which consists of over 50 individual largely monogenetic volcanoes. The most recent and largest eruption occurred 600 years ago, and was witnessed by local inhabitants. It is anticipated that the chance of reawakening of a dormant volcano is very low; however, a new volcano could be created at any time in a new location within the field. In order to study ground deformations in the Auckland region twenty six ENVISAT ASAR images (Track 151, Frame 6442, IS2, VV) were acquired, spanning the period from 18 July 2003 to 9 November 2007. Over a hundred differential interferograms with perpendicular baselines of less than 500 meters were calculated and analyzed. Stacking, Small Baseline Subset and Permanent Scatterers processing algorithms were used to determine spatial and temporal patterns of surface deformation as well as average rates. A number of localized deformation regions were consistently observed by all three techniques. Three regions of subsidence are believed to be caused by groundwater extraction. The nature of uplifts is currently unclear, but a linear feature paralleling the regional tectonic fabric may be related to a hidden fault. The observed temporal deformation pattern is noisy but appears to be close to linear.