Mr Green said the plan would outline the roles and responsibilities of everyone involved to reduce risk and prepare for, respond and recover from emergencies.
“Cyclone events are severe weather events whereas a Hikurangi magnitude 9 earthquake and tsunami presents a catastrophic scenario based on the level of damage and impact across multiple regions.
“The plan provides the basis for the coordination of all agencies who are part of the initial stage of response both at national and regional levels.
“This means actions can be undertaken immediately, given we have a plan.
“In short, the emergency response planning will make sure we all know what to do.”
Mr Green said this week’s planning hui followed the Hikurangi M9 workshops last year, where scientists and tsunami experts visited the region to share information about the Hikurangi faultline science and disaster response planning.
In 2021, GNS Science released an updated risk advisory that highlighted a 25 percent chance of a significant event in the Hikurangi subduction zone in the next 25 years.
“These are considerable odds.”
National Emergency Management Agency (NEMA) also held planning workshops at Parliament last year where a draft national CATPLAN plan was developed.
“NEMA has shared this with us as we develop our regional plan.
“We will let our community know the outcome of this three-day event,” Mr Green said.
“Part of being ready for any emergency is making sure our community is aware of what to do, where to go and be reassured that those who will help them have a plan.
“The ability to be able to think on your feet during these catastrophic events to reduce the loss of life is part of what makes someone a first responder.
“Being able to bring together first responders and community partners to plan brings huge benefits for our community.”
The scenario envisioned by scientists imagines a huge “megathrust” earthquake that would batter Gisborne with multiple tsunami and high-magnitude aftershocks.
The Hikurangi subduction zone runs the length of the North Island’s East Coast, passing as close as 40km offshore from Gisborne.
The scenario
Just after 9am on a school day in winter, a magnitude 8.9 earthquake occurs on the Hikurangi plate boundary, sparking intense shaking along the whole east coast of the North Island between Wellington and East Cape.
Between Mahia and East Cape, the duration of intense shaking is very long, with a severe ground shaking of more than 60 seconds. The shaking sets off many landslides, exacerbated by typically wet winter conditions.
This would be felt as a long or strong earthquake and official emergency management advice for such an event is for people to evacuate immediately to high ground or inland, on foot or bicycle.
The worst affected regions are Wellington and the East Cape, where the landslides are comparable to those in Marlborough after the 2016 Kaikoura earthquake.
The earthquake has also changed the landscape, creating a deformation offshore 50-100km wide and 600km long, two to three metres offshore. This creates a tsunami, which spreads to the coast.
The scenario envisages run-up heights along the east coast frequently in the 7m to 10m range, and in some localised places, as high as 20 metres.
Tsunami waves continue to batter the coast for several hours (and persist as a marine threat for over a day). At the same time, a series of large aftershocks begin that will continue for several weeks (and will include several events over magnitude 7, which in turn prompt further tsunami warnings and evacuations).
In Gisborne, the strength of shaking causes 10 to 20 buildings to collapse, both commercial and residential, with parapet damage a particular problem.
The earthquake has caused fatalities, and injuries. The tsunami causes more, disproportionately distributed among people with reduced mobility.
Hospitals and medical centres just about manage to cope but about 1000 people are permanently displaced, mostly due to tsunami damage.
