The earthquake is predicted to be felt across the country if the Alpine Fault line ruptures.

A large earthquake on the fault line has occurred roughly every 300 years over the previous 8000 years. The most recent one occurred in 1717.

According to research conducted over the last two decades, there is a 75% risk of an earthquake on the Alpine Fault occurring in the next 50 years, with an 82 percent chance that it will be larger than an eight on the Richter scale.

We can prepare for this one, which is known as AF8.

According to Dr. Caroline Orchiston, the ground motion of a magnitude 8 earthquake causes a cascade of events.

"The mountains tremble a lot, causing landslides and maybe damming rivers or crossroads."

Orchiston is the science lead for the AF8 campaign, which is a collaboration between Civil Defence Emergency Management and Alpine Fault scientists to disseminate scientific data to those who need to know.

Scientists have estimated that if it ruptures, ground tremors will begin near Milford Sound and spread all the way down the South Island, she said.

A 350-400km surface rupture of the Alpine Fault is also expected, as the fault breaks right through to the surface.

"The movement over that surface rupture will be around 10 meters horizontally and two or three meters vertically."

"Any road, bridge, or township that spans the fault will be severely devastated."

An alpine fault earthquake will also have a substantial impact on the electrical grid.