40 minutes to get to safety if quake hits

: A new evacuation map is set to be released incorporating information from this map, which shows the areas that are likely to be affected by a 14m tsunami. Photo/Supplied

Miserable and wet, but alive - this is the latest prediction of what will happen if people react quickly to the threat of a worst-case tsunami hitting Papamoa and Mount Maunganui.

Data based on a enormous magnitude 9 earthquake along the Kermadec Trench running north-east from the Bay of Plenty is being translated into an evacuation map for Tauranga's vulnerable low-lying suburbs.

And while details of the map were still being refined, the council's emergency management spokesman, Paul Baunton, said it showed people could survive a 14-metre tsunami provided they responded quickly to the warning signs.

"It is hopeful, it will give people heart."

Although the tsunami would top the dunes and slosh inland via the Kaituna River and harbour entrance, most people would only get their feet wet if they started heading for the hills as soon as they were rocked by an earthquake lasting over a minute.

Mr Baunton said the map to be published in August would highlight the tsunami flowpaths, safe areas and how far back from the coast people needed to reach to avoid being swept away.

The biggest threat to Tauranga was from an enormous vertical rupture along the Kermadec Trench where the Pacific Plate was sliding under the Australian Plate.

He said lessons had been learned from the rupture of a similar fault line off the Japanese coast in 2011 when a magnitude 9.1 earthquake unleashed a tsunami that killed 18,000 people.

By calculating the strength of the surge with topographical and other landscape details, emergency managers were now well down the track to understanding exactly where people needed to be to have a really good chance of survival when the tsunami arrived in 50 minutes.

Mr Baunton said they were allowing 40 minutes for people to get to safety once they had gathered their wits after the big shake and grabbed evacuation kits.

If Papamoa people set off inland at a strolling pace of 2.5km/h, then the worst they would get was wet. Each feature of land led to the tsunami losing energy and height, with the Wairakei Stream basin soaking up a lot of the energy - the area behind the stream was low risk.

"Once people have crossed that barrier, the likelihood is that they will just get wet, with a high survival rate."

The evacuation area map would have a 1.5m freeboard margin of error because they were dealing with a phenomenon not as well known as storm flooding. "The mechanisms of tsunamis are a lot less known."

The 40-minute maximum period to reach safety was also based on people using roads to get inland. "Most people will take a direct route and not care about whose properties they walked over to save their lives.".

Mr Baunton stressed that if people relied on authorities telling them when to evacuate, the tsunami would have arrived. The lesson from the Japan tsunami was that everyone should be self-reliant.

The map would show the safe places that people needed to reach within 40 minutes and the best routes to get there.

Planning would include an order of priority to evacuate people that were not able-bodied.