Geologists dig up faultline to forecast next big quake

Geologists are digging into New Zealand's biggest faultline to forecast when the next big earthquake will strike on it, with interest heightened by Sunday's 5.7 magnitude tremor in Christchurch.

When the Greendale Fault ruptured with a 7.1 magnitude quake five years ago, geologists worldwide turned to New Zealand.

And with thousands of quakes since, including Sunday's big shake, that interest has not waned.

The Alpine fault is under scrutiny at the moment with work underway to predict the next earthquake at the top of the South Island. Source: 1 NEWS

Geologist are working near Springs Junction in the upper South Island, creating two 20-metre-long trenches so they can explore the northern end of the Alpine Fault, New Zealand's biggest.

Their hope is to date the last three earthquakes, over a period of 2000 years, to show the frequency of the faultline's activity.

Earthquake geologist Robert Langridge says they'll take samples from the deposits to radio carbon date and understand the timing of past earthquakes.

Each sample, gathered meticulously, will take three months to process.

"By understanding when these earthquakes happened and how far apart they were in time, we can have some forecast if you like of how far it is in the future till the next large earthquake," Mr Langridge said.

Until this project, geologists have focussed on the central and southern end of the fault because of the greater frequency of earthquakes generated in those areas.

The work near Springs Junction could provide an idea of the size and type of earthquake to expect at the northern end in the future.

"The results from our work will help us understand the hazards posed by the Alpine Fault," Mr Langridge said.

The next stage of the project will see more trenches dug just south of the current worksite as the geologists' quest for answers continues.