Breakthrough in earthquake faulting research to help assess New Zealand seismic risk

Scientists have discovered there is no connection between major fault lines in the North and South islands through central Cook Strait meaning that an earthquake fault rupture may be contained to one island if it occurred.

The findings are part of research released today by the National Institute of Water & Atmospheric Research (NIWA) which provides vital new information to help assess the potential hazard of earthquakes in New Zealand.

It is the first time scientists have been able to comprehensively map the active offshore faults in the Wellington and Cook Strait region – New Zealand’s most active seismic risk area.

NIWA has mapped about 20 active faults in the Wellington and Cook Strait region capable of generating earthquakes of magnitude M7 or greater, but none of them connect from the North Island to the South Island. Some of the faults are the offshore extensions of large faults on land, whereas others are entirely submarin.

The two-year study of the seafloor, supported by NIWA’s deepwater research vessel Tangaroa, together with new and archived seismic profiles from other sources, gives the first clear picture of all active faults in the offshore region.

The work is part of the project “It’s Our Fault”, jointly funded by the Earthquake Commission, Wellington City Council and ACC, which involves a comprehensive review of the likelihood, size, location and likely impact of large earthquakes in the Wellington region.

These new findings by NIWA will assist the project, which includes studies by GNS Science and Victoria University of the major faults on land and modeling of the potential impacts of future earthquakes.

NIWA’s Ocean Geology Principal Scientist, Dr Philip Barnes says the new findings are a breakthrough for earthquake research in New Zealand.

“We finally know what the big faults between Wellington and Blenheim are doing. By combining the seafloor imagery with other data of the faulted sediments and rocks beneath the seabed we have been able to get a much more accurate idea of the location, size and history of faults in the area.”

“The general discontinuity of active faults across Cook Strait has important implications for how we interpret the size and location of future earthquakes in the region. By determining the rate of activity on the faults over many thousands of years, we can also estimate the interval of time between earthquakes on each fault. This information has been added to the onshore active fault database at GNS Science to create a complete picture of the region, which can be used to provide new estimates of the likelihood of earthquakes occurring,” Dr Barnes says.

For the first time NIWA scientists have also been able to use high resolution images of the sedimentary layers below the seabed to assess the prehistoric earthquake activity of some of the faults – dating back as far as 18,000 years ago.

GNS Science Geologist, and Project Leader for the It’s Our Fault project, Russ Van Dissen says “knowing that there is no connection between the North and South island major fault lines will have a critical impact on the accuracy of modeling to assess earthquake risk.”

“Accurate forecasting of potential earthquake hazard is essential to many agencies including emergency managers, regional councils and insurers. This collaborative work will greatly improve our ability to assess the reality of the earthquake risk and potential impact.”

For more information contact:

Russell Van Dissen
Project Leader for It’s Our Fault Project
GNS Science