Ten metre tsunami could hit Hawke's Bay with 'no warning' after Hikurangi quake

Scientists told an audience in Napier that they are unlikely to get an official warning when the Hikurangi subduction zone just offshore eventually triggers a large earthquake and subsequent tsunami.

At an event on Wednesday last week, scientists from GNS science and NIWA, as well as local government officials, hosted a talk at the Napier Conference Centre outlining the threat posed to Hawke's Bay communities from the fault.

The Hikurangi subduction zone lies just east of the North Island, and is the area where the Pacific tectonic plate is sliding under the Australasian Plate.

Dr Kate Clark of GNS Science said about $60 million of international funding has been secured to study the zone within the next two years, and also outlined timeframes around plate movements.

"The Hikurangi subduction zone is the largest local source of tsunami hazard," Dr Clark said.

"The subduction zone is very close - so the timing between when the earthquake occurs and when waves start arriving is likely to be too short for the issuing of official warnings - so that's why there is a lot of emphasis on self evacuation ... the key message here is 'long or strong, get gone'.

"If you feel a long earthquake - about a minute of shaking - or a very strong earthquake, so something where it's very hard to stand up - self evacuate.

"Don't linger around and wait for an official warning."

Dr Clark said data shows large subduction earthquakes have occurred along the fault in the past, and those quakes are likely to produce significant coastal movement and tsunami.

Sampling and research has shown that about eight major subduction earthquakes have taken place along the zone over the past 7000 years, recurring on average every 800-900 years, but some have had intervals as short as 200 years.

The last major subduction quake was between 500-600 years ago.

Hawke's Bay Civil Defence emergency management adviser Jim Tetlow said in the "worst-case scenario", a tsunami of up to 10m in height could be generated by the next quake, and it could reach as far as 6km inland.

An interactive map was recently created to illustrate the different areas of Hawke's Bay which would likely be affected by a large tsunami, and to what degree.

Evacuation zones include the majority of Napier, Wairora and Gisborne.

Dr Clark said Napier's deadly 1931 earthquake was not actualyl a "subduction" type of earthquake, but an "upper plate" event.

In February and March next year, GNS Science will carry out a series of controlled underground explosions as part of the organisation's SHIRE project in order to take seismic energy measurements.

They previously carried out similar experiments near Wellington in 2009.