Some of these are still rising, and the interplay between the tectonic forces pushing the mountains up and gravity trying to pull them down means that landslides are a common occurrence over much of New Zealand. The plate boundary zone in New Zealand Click on thumbnail for bigger image Tectonic plates behave like rigid shells that slide over the surface of a sphere. The biggest plate, the Pacific, is more than 10,000 km across. Almost all of New Zealand is in the deforming plate boundary zone. Only Northland is fully on the Australian plate, and only offshore islands like Chatham Island and Campbell Island are fully on the Pacific plate.
Large earthquakes are the most obvious sign of the deformation between the two plates.
When one side of a geological fault moves several metres relative to the other side, as in the 1987 Edgecumbe earthquake or the 1855 Wairarapa earthquake it is obvious that a lot of motion has occurred. Indeed, the earthquakes are themselves a response to this motion. It's similar to bending a stick. From these we now have a detailed picture of the average deformation that has occurred over just the last 4 or 5 years. It's more accurate in some places, less accurate in others, depending on the number of measurements we have made.