You are using an older browser version. Please use a supported version for the best MSN experience.

'Unusual' Taranaki quakes may hold clues

NZ Newswire logoNZ Newswire 1/02/2017
A Victoria University study investigated the earthquakes that occur beneath the line between the volcanoes of Mount Taranaki and Mount Ruapehu. © Rex Images A Victoria University study investigated the earthquakes that occur beneath the line between the volcanoes of Mount Taranaki and Mount Ruapehu.

A cluster of "unusual" earthquakes beneath Taranaki could prove significant in understanding how New Zealand's landmass was created.

A Victoria University study investigated the earthquakes that occur beneath the line between the volcanoes of Mount Taranaki and Mount Ruapehu.

Lead author Dr Jesse Dimech says the quakes are up to 52km deep, where most others in regular continental regions are restricted to the top 20km.

Dr Dimech says they also lie in the Earth's mantle, beneath the crust, defining an east-west boundary, or structure.

This is in contrast to the strong northeast-southwest grain for most geological structures in New Zealand.

The study has been published in the US journal Geology and co-author Professor Tim Stern says the earthquakes are all less than magnitude five and don't represent a significant hazard.

However, they help to explain the rapid rise and fall of the mountain ranges of the western North Island in the last five million years.

Prof Stern says geologists have long puzzled over the fact that much of central and western North Island rose above sea level in the last few million years, whereas south of Whanganui a once high-standing mountain range now lies underwater.

"We know that the tectonic plates have a deeper layer of mantle rock which is actually denser than the overlying crust," he said.

"We think the deep earthquakes beneath Taranaki are being triggered as this dense mantle layer peels off, and sinks into the hotter and less dense regions below."

The authors believe the "peeling off" may have caused the uplift of the western and central North Island from a few kilometres below sea level to average elevations of approximately 500 metres above sea level today.

image beaconimage beaconimage beacon