Then entrance to Thrust Creek, with gravels in the cliff on the right. J.Thomson / GNS Science
A thrust (or reverse) fault is where the rock on one side is pushed up and over the rock on the other side of the fault because the crust is being squeezed or compressed.
At Thrust Creek, the rocks to the west of the fault is greywacke - the ancient rock that underlies the Wellington region as well as the Rimutakas and other North Island ranges. On the east side of the fault are much younger gravels (about 50 000 years old). The west side has been thrust up over the east side and in so doing has pushed flat lying beach gravels into the vertical.
The Wharekauhau Thrust is a branch that splays out at the southern end of the Wairarapa Fault in the Palliser Bay area. It continues southwards through the sea floor towards Cook Strait. The fault displaced the sea floor and generated a 10 metre high tsunami that accompanied the 1855 earthquake that is estimated to have exceeded magnitude 8.2.
Thrust Creek is of great historic and philosophical significance, not just in New Zealand, but globally.
The eminent 19th century British geologist Sir Charles Lyell reported on the 1855 Wairarapa Earthquake, publishing in the Proceedings of the Royal Society of London in 1858.
In so doing, he demonstrated for the first time in the scientific literature, that there is a direct relationship between fault movements and earthquakes.Lyell never visited New Zealand, but he interviewed three people who had experienced the 1855 earthquake and who observed and recorded changes in the environment. Those were Edward Roberts, Walter Mantell and Frederick Weld. All three held significant roles in colonial New Zealand society.