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Published Wednesday, December 6, 2017
North Island of New Zealand was struck with 3 earthquakes this morning, with magnitudes of 4.6 and 4.7. No damage reported at this moment.
The natural threat posed by New Zealand's largest fault, the Hikurangi Subduction Zone, has again been in the NZ Herald headlines. Although the system is capable of generating earthquakes larger than 8.0 - and perhaps 9.0 - GNS Science earthquake geologist Dr Ursula Cochran says we shouldn't feel frightened. Instead, we should be prepared.
The Hikurangi Subduction Zone is New Zealand's largest fault because of the area that could move in a large earthquake.
Geological and geophysical evidence shows that the zone can produce magnitude 8.0 and larger earthquakes.
It is possible it could produce magnitude 9 earthquakes but we don't yet have strong evidence for this.
Geological evidence suggests the last magnitude 8 earthquake happened about 500 years ago and there were two magnitude 7+ earthquakes offshore of Gisborne in 1947.
One of main hazards of a large Hikurangi subduction zone earthquake is the tsunami it would trigger.
Modelling shows that parts of the East Coast close to the subduction zone - like eastern Wairarapa - could receive the tsunami about seven minutes after the earthquake.
Most locations will have longer gaps between the earthquake and the tsunami.
However, these short arrival times illustrate why it is so important to evacuate without waiting for an official warning — there will be no time to give one.
If you feel shaking that is long or strong, move away from the coast.
Don't be scared, be prepared, said Science earthquake geologist Dr Ursula Cochran for NZ Herald.
Scientists are keeping a closer eye on a large North Island fault zone that appears to be "locked" and bottling up stress that could one day cause it to snap, resulting in a huge earthquake.
The plate boundary fault, Hikurangi subduction zone, underlies the North Island and northern South Island, and continues offshore of the North Island's east coast.
GNS Science geophysicists have been watching it for many years, with highly sensitive GPS measurements of land movement in the North Island.
These measurements suggest that the fault beneath the lower North Island is currently "stuck".
When the fault region does finally become un-stuck, scientists expect to see a massive amount of pent-up energy suddenly released.
In 2011, the same process unfolded with catastrophic consequences when built-up stress on a subduction zone off the coast of Japan unleashed a 9.0 megathrust earthquake and tsunami that killed nearly 16,000 people.