Trough could help probe big quakes

A deep marine trough off the New Zealand coast will help international scientists understand more about the world's largest earthquakes.

The Hikurangi Trench, or subduction zone, lies less than 100km off the east coast of the North Island and runs south to offshore off Kaikoura.

It marks the boundary between two crustal plates and the margin where the Pacific Plate, to the east, is being dragged underneath the Australian Plate.

Visiting United States seismologist Kevin Furlong said the trough, and two similar trenches off the coast of North America and Alaska, would form the focus of a major global study of megathrust earthquakes, which can often be of magnitude 9.0 or higher and cause highly damaging tsunamis.

The Pennsylvania State University professor gave a seminar at Canterbury University on Thursday outlining new research on subduction zone quakes.

Recent megathrust earthquakes include:

Japan, March 2011, magnitude 9.0.

Sumatra, Boxing Day 2004, magnitude 9.1.

Alaska, Good Friday 1964, magnitude 9.2.

Chile, 1960, magnitude 9.5 (the largest quake known).

Furlong told The Press detailed scientific understanding of subduction quakes was still in its infancy.

Plate tectonics had only developed since the mid-1960s as a theory to explain processes and events such as quakes and vulcanism.

"Before plate tectonics really got developed, the last big [megathrust] one was the 1964 Alaskan quake," Furlong said.

"But then there was a 40-year window between then and the Boxing Day 2004, Sumatran, quake."

Each megathrust quake had left scientists scratching their heads when it failed to behave as their modelling, based on such a small number of events, had predicted, Furlong said.

"It was clear we didn't really have a very complete picture of how big subduction quakes happen."

The Hikurangi Trench was one of the world's big seismic unknowns, he said. It could be as hazardous to New Zealand, especially the eastern North Island, as a similar zone that caused Japan's devastating magnitude-9.0 quake and tsunami in March 2011.

Researchers participating in the international GeoPRISMS programme would research the trough, with plans to drill into the subduction zone. "This subduction zone will have its own nuances, like they all do, so we have to look at which of those matter and which don't," Furlong said.

The Press