The Alpine Fault runs along the foot of the steep rangefront, extending right up the West Coast of the South Island. The mountains are therefore part of the Pacific Plate and all the flat land in front, made up of glacial outwash gravels, is on the Australian Plate.
At Gaunt Creek near Whataroa, you can get right up close to a cliff exposure of the Alpine Fault. The pale green rocks in the foreground have endured being crushed and uplifted along the fault line. They have been altered into what is known as cataclasite, consisting of clay and lots of crushed rock fragments.
A more distant view of the cliff section from the creek shows how the uplifted rocks have over-ridden the gravels which are about 15 to 16 thousand years old. The two white arrows show the line of the fault.
A short distance away is the Deep Fault Drilling Project (DFDP1) Observatory that was set up after two boreholes were drilled here in 2011. The fault is dipping at about a 40 degree angle, and the boreholes were positioned to intercept it at around 100m depth.
For a bit more background to the DFDP have a look at this previous post from 2011