Leading New Zealand scientists have designed a credible scenario for an
earthquake and tsunami on the Hikurangi Subduction Zone. The scenario, further
developed by GNS Science experts, helps emergency responders to plan and prepare
for a magnitude 8.9 earthquake and tsunami on the Hikurangi Subduction Zone
which is off the east coast of the North Island.
The scenario shows impacts from the earthquake and tsunami for the most effected areas
across the North Island's East Coast in New Zealand. It is one of many possible
scenarios and does not predict the future. It is unlikely that a Hikurangi
Subduction Zone earthquake and tsunami will happen exactly like this.
This scenario is based on a magnitude 8.9 earthquake and shows the potential
levels of ground shaking. The earthquake's rupture begins 70 kilometres off the coast
Porangahau, Hawke's Bay at a shallow depth of nine kilometres.
An earthquake like this would release around 45 times more energy than the
2016 magnitude 7.8 Kaikoura Hurunui earthquake.
The scenario is run at double the actual speed and the scale bar shows the level of shaking.
White shows extreme shaking and red shows strong to severe shaking.
The earthquake rupture continues north and south creating long and strong shaking
along the east coast of the North Island. Gisborne would experience particularly
strong and long shaking in this scenario due to the different rock types in the area
that increase the shaking's intensity and duration. Wellington would
feel ground shaking 90 seconds after the initial earthquake rupture. Areas further
away from the earthquake rupture would experience strong shaking. For example
Auckland though a good distance away would experience around 30 seconds of
severe shaking. As well as the shaking the earthquake would potentially cause
liquefaction, landslides and fires in some areas.
The sudden movement of the sea floor during the earthquake causes
a lot of water to move creating a tsunami.
The scenario is now showing the tsunami created by this large earthquake.
Within the first few minutes there are rapid changes in sea level along the east coast of the North Island.
The tsunami moves in all directions.
After the earthquake rupture some parts of the coast may see a rise in sea level
shown in red. In others such as Hawke's Bay in this scenario
the sea-level would rapidly decrease, pulling away from the coast and
returning with enormous speed and force when the tsunami waves arrive. This is
shown in blue. This is because the ocean first draws down and sucks water away
from the coastlines to later return. Close to the shore along the East Coast
waves could reach about ten metres above normal sea level in some places.
In a few locations where the tsunami is funneled into steep valleys on shore
It might reach even higher, possibly up to 20 metres above sea level. In some other
earthquake scenarios run-up heights could be even greater than 20 metres at some locations.
Tsunami evacuation zones account for multiple possible earthquake scenarios.
In this scenario the speed the tsunami waves travel means
there would not be enough time for an official evacuation warning.
The long or strong earthquake is your signal to self evacuate all tsunami evacuation zones.
Check your tsunami evacuation zones on your local civil defense group website.
Make sure that you and your family and others who rely on you know your
evacuation route to higher ground or inland whether you're at home, at work, at
school or out and about. In this scenario around 13 minutes after shaking begins
in Wellington large tsunami waves arrive at the harbour entrance and extend into
the tsunami evacuation zones. It's important to evacuate all tsunami
evacuation zones in a long or strong earthquake. The scenario is sped up to
show how the tsunami moves in the first two hours of the earthquake. The tsunami
would reach cities as far away as Auckland, Christchurch and even the West
Coast of the North Island. While this and other science-based scenarios do not
predict the future and a single scenario cannot provide all the answers on its
own, they help emergency managers to plan and prepare for events like a Hikurangi
subduction zone earthquake and tsunami. To get prepared visit getready.govt nz
To check your tsunami evacuation zones visit your local civil defense emergency management website.