New fault investigated ten years on from Christchurch

New Zealand’s Prime Minister Jacinda Ardern has attended a service held in memory of the 185 people who died when a 6.3 magnitude earthquake hit Christchurch ten years ago.

The earthquake, an aftershock of the September 2010 Canterbury Earthquake, flattened buildings and destroyed homes. Before these events, Christchurch was not viewed as one of the nation’s seismic hotspots.

A decade on, GNS Science experts have embarked on a research project to determine the earthquake risk of a recently discovered fault in the Waikato. It is part of an effort to better understand quake risk in parts of New Zealand that are traditionally seen as safe from quakes, according to the New Zealand Earthquake Commission (EQC). 

Thanks to improved aerial mapping tools, scientists recently discovered the Te Puninga fault, 27km from Hamilton, that could potentially generate a 6.7 magnitude earthquake.

Dr Pilar Villamor, an earthquake geologist at GNS Science, is heading up an EQC-funded project to study the fault, about 3km from Morrinsville. She says that researchers estimate the fault could generate a 6.7 magnitude earthquake based on its length of 25km.

“If it ruptured, Morrinsville would potentially experience the same level of shaking Christchurch had during the 2010 Darfield quake. And it would be relatively strong in Hamilton as well.”

Dr Villamor’s team will dig trenches across the fault to expose soil layers displaced in previous earthquakes over the past 20,000 years and take samples from each layer. The samples will be dated by experts at the University of Waikato and in Spain.

“This will tell us how often the fault has ruptured, and the magnitude of the quakes it has produced,” she says. ”That information in turn will help us to understand the risk of future earthquakes in the area and how to prepare for that risk,” she says.

According to Earthquake Commission research manager Dr Natalie Balfour, the research is extremely important for the communities in the Hauraki Plains, which has traditionally been considered a low seismicity area, not unlike the Canterbury region before 2010.

“We’re funding this project and similar work in other parts of the country to get a much better idea of the risk in areas that New Zealanders generally think of as safe from earthquakes. 

“Research shows us that many of these areas have had large earthquakes in the past, and detailed historic data will help understand what could happen in future,” says Dr Balfour. “This will help communities make decisions about how to be better prepared for future events.”