About 1000 deaths, thousands of injuries and extensive destruction along the east coast of the North Island - this will be the result of a tsunami triggered by an earthquake in the Hikurangi subduction zone under a scenario presented by GNS Science.
The scenario, in a report prepared for the purpose of developing a response plan, is considered serious and credible, but comes with the obvious caveat that there is no way of telling what any earthquake or tsunami would look like.
This scenario is based on an Mw 8.9 earthquake in the southern part of the Hikurangi subduction zone, creating a strong slip on the ocean floor in the southern Wairarapa/Cook Strait area.
It hits just after 9am on a winter school day. It sees intense shaking along the whole east coast of the North Island, and initiates a tsunami that rapidly reaches the coast, with wave heights of 7-10 metres, and 20m in some localised places.
In Wellington the shaking is very intense, with destruction in the city's CBD similar to that seen in Christchurch in the 2011 quake.
"A large landslide near Karori has engulfed 20 homes, and one near Days Bay has destroyed 15 houses. Ten cars are trapped on State Highway 2 within a landslide between Wellington and Petone," in the scenario.
Landslides isolate the city from the rest of the country, liquefaction is widespread and fires break out.
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"The first tsunami waves reach the south coast of Wellington after 10 minutes and the inner harbour areas like Petone after about 30 minutes," it said.
The largest waves strike 40-60 minutes after the quake. Waves reach a height of 7-8 metres at the coast. Inundation in Wellington is mitigated by the ground being uplifted 1.5-2 metres, but still the waves inundate 2 kilometres inland of Petone. The worst hit areas are Lyall Bay and Eastbourne, but there is significant inundation in Seatoun, Evans Bay, the CBD, Petone and Seaview.
The southern end of the runway is covered by several centimetres of sand and debris.
People rush to higher ground, but some are inevitably caught in the waves, especially the less mobile. The elderly, the disabled and those living in areas where it arrived most quickly are disproportionately represented among the estimated 500 casualties and 5000 injured.
In the Napier CBD 10 buildings collapse, liquefaction is widespread and there is widespread tilting of buildings on their foundations and roads and bridges are damaged.
The first major wave arrives about 20 minutes after the quake, peaking at 30-50 minutes. A second, more severe, wave hits 140-160 minutes after the quake. The waves cause widespread damage to houses in Westshore, Ahuriri, Clive, Haumoana and Te Awanga.
There is severe damage to the port, with logs and containers exacerbating damage to Westshore and Ahuriri.
Napier is cut off by road, the airport is unusable due to damage and liquefaction.
A large-scale evacuation of the city CBD sees people rush up Bluff Hill, but those in other areas - particularly Westshore and Clive - have trouble evacuating due to liquefaction and the destruction of bridges. About 200 people die and 700 are injured.
In Gisborne 10-20 buildings collapse before the first large wave rises about 10 minutes after the quake. The wave peaks 20-40 minutes after the quake, and is larger again 80-100 minutes after the quake.
The area is cut off from the rest of the country, but the airport remains usable. About 90 people are killed and 500 injured.
In Tauranga there is intense shaking, but minor damage to buildings and minor liquefaction. A small series of tsunami waves follow, but there are no deaths and about 50 injuries.
The rest of the country is also affected, bringing the total number of casualties to about 1000, with about 10,000 injuries.
The report considers four other scenarios, with variations to the type of slip and the location. These result in more or less damage in each city depending on the scenario.
The report writers go to lengths to state that the scenario was created for planning exercises and "must not be used as the basis for assessing the risk to any particular property or person and must not be used as the basis for any site-specific engineering work".
"A striking feature of the scenario is the wide geographical spread of damage that can occur in such a large earthquake, which will present serious challenges for how to restore normal living conditions," the writers said.
Project Leader of East Coast LAB (Life at the Boundary) Kate Boersen said the work was about "planning and preparing as best as we can for a large earthquake and tsunami."
"There is a careful balance between informing people of our earthquake and tsunami risk so they have a realistic expectations of what an event of this size will look like and avoiding overwhelming people, as we know this can lead to fatalism," she said.
"We focus on the simple things we can all do to plan and prepare such as practicing your drop cover hold or tsunami evacuation route".
Jeremy Holmes, Regional Manager at the Wellington Region Emergency Management Office (WREMO) said the likelihood of a large earthquake and tsunami was low, but the potential impact could be significant.
"A major rupture of the Hikurangi Subduction Zone is likely to be a national level emergency, similar to the Christchurch Earthquake in 2011," Holmes said.
Its affect was likely to be far larger than what was experienced in Wellington in 2016, during the Kaikōura Earthquake - the effects of which were still being felt three years later.
WREMO and councils had been working with communities and businesses to encourage them to be better prepared, he said.
That included the development and distribution of the Earthquake Planning Guide into all households in the Wellington region, its translation into 16 languages, holding free continuity workshops for businesses to help improve their level of preparedness for such large-scale events, and working with key providers to make infrastructure more resilient.
"in 2018 we released the Wellington Region's Earthquake Response Plan, which sets out the way in which the region's official response agencies and organisations will respond to such a large scale event," Holmes said.
The Minister of Civil Defence, Peeni Henare, said preparing for emergencies such as tsunami could seem overwhelming "but it's easier than you think".
"Make a plan, find out where the safe tsunami locations are and decide where you'll meet," he said.
A tsunami hīkoi had been added to the yearly ShakeOut exercise to make preparedness an every day part of living.
PRELIMINARY IMPACTS SCENARIO:
WELLINGTON:- Very intense shaking, particularly damaging to vulnerable buildings (eg un-reinforced masonry buildings).
- Impact on CBD area comparable to that in Christchurch CBD following February, 2011, earthquake.
- Almost all buildings are damaged. About 50 buildings have collapsed partially or completely.
- Severe landslides across region will take weeks to clear. City is isolated from rest of country.
- Liquefaction occurs around Petone, the CBD, Evans Bay and Kilbirnie. Roads, pipes and cable network damaged.
- First tsunami reaches south coast after 10 minutes. Larger waves strike after 40 minutes and 60 minutes. Maximum height of 7-8 metres.
- Inundation extends up to 2km inland of Petone and about 4km up the Hutt River.
- Worst hit areas are Lyall Bay and Eastbourne, though there is also significant inundation in Seatoun, Evans Bay, the CBD, Petone and Seaview.
- The southern end of the runway is inundated and covered in several centimetres of sand and floating debris.
- In Seaview small boats from the marina have been floated onshore.
- Fires break out. Debris and lack of water make them difficult to fight and contain.
- The intense shaking leads to widespread self-evacuation but some people are caught in the tsunami. Casualties are disproportionately distributed among the less-mobile such as the elderly and disabled and those living in areas where waves struck most quickly, and those trapped by rubble or injured by falling glass.
- Electricity, gas, water and wastewater are all cut off. It will take 7-10 days to repair electricity infrastructure. Water supply will take months to fully restore.
- Total casualties = 500 fatalities and 5000 injuries. Further casualties due to secondary consequences such as fire and disease will depend on emergency response.
NAPIER:
- Intense shaking in and around Napier. Ten buildings in the city collapse with minor to moderate damage to most others.
- Liquefaction is widespread, with very high levels in CBD and Meeanee and to north around the airport.
- Marshland near airport subsides causing strong currents to start flowing from the Ahuriri lagoon.
- First major wave hits coast after about 20 minutes, reaching its peak at around 30-50 minutes, causing widespread flooding north and south of Napier. Second, more severe, wave peaks 140-160 minutes after quake.
- Waves cause severe damage to houses in Westshore, Ahuriri, Clive, Haumoana and Te Awanga.
- Napier is cut-off by road. Rail line will take weeks to repair. Airport is unusable die to tsunami damage, liquefaction and subsidence. The port is severely damaged.
- Large numbers of people evacuate to Bluff Hill. Residents at Westshore, Clive and Haumoana face difficult evacuation due to high levels of liquefaction. Most casualties occur in Westshore and Clive areas where damage to roads and bridges makes emergency access difficult.
- About 200 people die, and about 700 are injured.
- About 2000 people cannot return to their homes. Hastings does not suffer as much damage and many Napier residents relocate to Hastings once the roads are cleared to avoid repeated tsunami evacuations caused by aftershocks.
- Three days after the earthquake a gastroenteritis outbreak occurs due to unsanitary conditions and the lack of water mains for many people.
GISBORNE:
- Very intense shaking in Gisborne causes 10-20 buildings to collapse.
- Series of tsunami waves follow the earthquake. First wave starts to rise after about 10 minutes, and peaks 20-40 minutes after the earthquake. Waves cause widespread damage to commercial and residential areas south of the CBD.
- The SH35 bridge in the central city is destroyed.
- Farmland and marshland south of city is inundated.
- Port very badly damaged and requires lengthy and extensive repairs.
- Airport remains usable but lacks fuel and communications.
- Water and wastewater networks badly damaged and will takes weeks to repair.
- City is cut-off from the rest of the country by large landslides on all highways. They will take weeks to repair. Several small communities are completely isolated and lacking all utilities.
- About 90 people die and 500 are injured.
TAURANGA:
- Quake is fairly intense and enough to cause minor structural damage to some buildings.
- Light liquefaction around Mt Maunganui and Papamoa.
- A small series of tsunami waves arrive about an hour after the quake, but do not go far inland.
- Small boats in marinas are damages, there is minor damage to the port and railway bridges. The airport is unaffected.
- No deaths and about 50 injuries.
REST OF COUNTRY:
- In Auckland there is damage to some buildings, with about 200 people injured.
- Power is cut for about three hours in Auckland and most of the North Island.
- Ports and airports in Auckland, Tauranga, Palmerston North and Christchurch must cope with additional flights and ships that can no longer land or dock at their original destinations.
- Ferry services between the North and South Islands have been suspended due to damage to port in Wellington.
- SH1 in Marlborough closes due to slips.
- Helicopter operators are very busy ferrying vulnerable people and helping restore infrastructure. Many people struggle to re-unite with family members and wish to enter tsunami zones to look for pets.
Ministry of Civil Defence & Emergency Management Tsunami Warnings:
Long or Strong, Get Gone: If you're near the coast and experience any of the following:
* Feel a strong earthquake that makes it hard to stand up, or a weak rolling earthquake that lasts a minute or more
* See a sudden rise or fall in sea level
* Hear loud and unusual noises from the sea
Don't wait for an official warning: move immediately to the nearest high ground, out of all tsunami evacuation zones, or as far inland as possible.
You'll need to self-evacuate: In a local source tsunami, there won't be time for emergency services to go door to door to coordinate evacuations. You must be prepared to self-evacuate.
Know your evacuation route: Check out your local Civil Defence Emergency Management Group's website for your tsunami evacuation zone maps. Links to CDEM Groups tsunami evacuation zone maps can be found here. Practise your route.
Staying safe means staying informed: Know where to get information. Listen to the radio for updates. Warnings and evacuation maps will be issued via Emergency Mobile Alerts, the Civil Defence website, news media, and @NZCivilDefence Twitter.
Plan ahead if self-evacuation is a problem: If you have a disability or special requirements, make arrangements with your support network to alert you of any warnings and to help you evacuate.
Hīkoi not convoy: If possible, run, walk or cycle when evacuating from a tsunami. You don't want to get stuck in traffic in a tsunami zone.
Have a grab bag ready: Have a grab bag ready with food, water, warm clothes, a battery powered radio, and anything else you might need.
Don't forget animals: If you have pets, domestic animals or livestock, include them in your evacuation planning.
