Scientists probing Taranaki's hidden quake risk

Scientists will try to model the hidden earthquake risk below Taranaki. Photo / File

Ask any Taranaki resident what they think their biggest natural hazard is, and they'll likely turn and point to the dormant volcano that dominates their horizon.

However, several hundred quakes are recorded in the region each year – most of them in a region west of Mt Taranaki, called the Cape Egmont Fault Zone.

By taking a closer look at this hazard, scientists expect to learn much more about the active faults and associated earthquake risk in this energy-rich province.

Traditionally, hazard planners have relied upon evidence left by earthquakes and faulting in our past to work out what potential threats we may face in the future.

Several large earthquakes that recently shook the country have, however, highlighted some of the limitations in our current understanding of New Zealand's active faults and the earthquakes they generate.

The 7.1 Darfield Earthquake, which started a long-running sequence that included the devastating Christchurch Earthquake, struck on a fault that was previously unknown.

And the 7.8 Kaikoura earthquake – one of the most complex multi-fault earthquakes ever recorded – ruptured with a far-travelling ripple effect that surprised most earthquake scientists.

At present, some of New Zealand's leading earthquake scientists consider the National Seismic Hazard Model, which under-pins our building code, is likely to under-estimate earthquake sources with long recurrence intervals, or those capable of triggering such seismic cascades.

New Zealand earthquake scientists, like others around the globe, are now focused on identifying and modelling more accurate representations of active faults through the use of cutting-edge technology and data.

A pilot study, being led by GNS Science structural geologist Dr Hannu Seebeck, will use the Cape Egmont Fault Zone to test the ability in mapping complex active fault systems to depths up to 15km below the surface.

Three-dimensional modelling of this fault zone – developed from surface and sub-surface data – will ultimately show how faults rupturing at depth propagate to the surface over many earthquake cycles.

What makes Taranaki such an ideal place for this study is the extensive amount of publicly-available seismic reflection and exploration well data generated by the petroleum industry over the last 50 years.

Seebeck said the biggest challenge would be developing a cohesive dataset between onshore and offshore areas – not to mention the complexity of trying to retrace the geological evolution of the central Taranaki basin over the past 11 million years.

But the benefits would be enormous.

"The knowledge gained will provide accurate up-to-date information on earthquake hazard for this part of Taranaki - a region with nationally significant energy infrastructure."

All natural gas in New Zealand is currently produced and distributed through a series of pipelines from gas fields clustered around the Taranaki Peninsula.

Any earthquake big enough to disrupt this network, which comprises just over 20 per cent of our annual energy supply, could lead to losses estimated at between $400 million and $650m each month.

"Our research will also identify and refine potential tsunami sources - and is likely to have value for future tsunami hazard assessment in the Taranaki," he said.

"Although not a component of the present project, such tsunami modelling would have important implications for coastal installations, infrastructure and residential areas along the West Coast of the North Island and the northern South Island."

Beyond building local resilience, Seebeck said what scientists learn from the project could open up new directions in earthquake science.

"The results of this study could be used in both current methods to quantify hazard - and to calibrate the next generation seismic hazard models presently in development."

The study is being supported with a $728,600 grant from the Ministry of Business, Innovation and Employment's Endeavour Fund.