Historical survey measurements

Soon after Europeans arrived in New Zealand, surveys to determine land boundaries and make accurate maps were begun. These surveys used theodolites to measure angles between geodetic monuments - markers set in the ground. From these measurements the positions of the monuments could be determined relative to each other. These surveys eventually covered most of New Zealand, with the primary (or 1st order) geodetic triangulation of the country - carried out between the 1920s and 1940s - representing the pinnacle of this work. The black and white wooden or metal beacons that are a feature of the New Zealand countryside mark the positions of many of these geodetic monuments.

Many monuments were surveyed more than once over the years. By comparing the angles measured between a particular set of monuments that crossed the Alpine fault, the famous geologist and surveyor Harold Wellman noticed that some of the angles were changing at a more or less steady rate. He interpreted this to mean that the ground was deforming along the fault. By combining this with his geological observations of features that had been offset on either side of the fault, Wellman realised in the 1940s that the two sides of the Alpine fault had moved hundreds of kilometres relative to each other over many millions of years. Furthermore, this motion was still going on today. This insight was one of the pieces of geological evidence that led to the theory of plate tectonics 20 years later.

More recently Global Positioning Systems (GPS) surveys and continuous GPS is used to monitor deformation.