Key things you should know if you live along the Pegasus Bay or Banks Peninsula coast:

• If tsunami warning sirens sound, or you receive an official warning to evacuate, evacuate the coastal evacuation zones for your district (see below for more detail on where these are).  You will have several hours to evacuate.
• If you feel a moderate long (more than one minute) earthquake, evacuate the coastal evacuation zones for your district.  Do not wait for the sirens, or for an official warning - the earthquake is your tsunami warning.  You will have at least one hour, possibly two or three, to evacuate.
• If you feel very strong ground shaking, in which it is hard to stand up (at least a magnitude 6 earthquake), there is a very small chance that a small tsunami has been generated.  Move immediately away from the coast, estuaries or river mouths at least two blocks inland.  If you cannot quickly move at least two blocks inland (e.g. if you live in Southshore) consider going to the upper storey of a two storey building, or up onto a high sand dune - the highest sand dunes along the Pegasus Bay coast are higher than the expected worst case local source tsunami.  DO NOT WAIT FOR SIRENS, or for an official warning - the earthquake is your tsunami warning.  You may only have 5-30 minutes to evacuate.  
• If you are at all able, evacuate on foot or by bicycle to avoid traffic jams.  You are much more likely to get out if you are on foot or on a bicycle and you will leave more room on the road for those people who must use a car.

Below is more information on the different types of tsunami and what you should know and do.

Local source tsunamis (tsunamis created in Pegasus Bay)

• Local source tsunamis are tsunamis that are generated less than one hour's travel time away from the coast.  For the Pegasus Bay coast and Banks Peninsula that means tsunamis created within Pegasus Bay.
• The chances of a local source tsunami being generated by an earthquake in Pegasus Bay are low and have not changed significantly as a result of the recent earthquakes.
• Scientists have discovered some earthquake faults on the sea floor in Pegasus Bay, but they appear to move very infrequently (once every few thousand or tens of thousands of years). They are not thought to be big enough, and would not produce enough vertical movement, to create a significant tsunami that would flood large amounts of land.

• If one of these faults were to move, the chances of a tsunami being generated is very very small.  In the absolute worst case, tsunami modellers think that the largest tsunami that could be created would be around 1.5 metres at the coast, above normal sea level at the time.  On steep shores, where there are high sand dunes or cliffs-3 metres on land above sea level at the time. If it happened at high tide, that means it could reach 4 metres above mean (average) sea level right at the coast, but would drop away quickly inland.  Scientists have not found any faults in Pegasus Bay that could create a really big tsunami, like they have in other parts of New Zealand.
• If a 1-3 metre tsunami was generated by a fault in Pegasus Bay, the first surge could arrive within about 5 minutes of the earthquake.
• If you are on the beach or within two blocks of the coast, estuary or a river mouth and feel strong ground shaking that makes it hard to stand up, move inland or away from the estuary or river mouth at least two blocks or to higher ground (at least 4 metres high) as quickly as you can, using the safest route that you can.  Within those first two blocks, every step you move inland or uphill makes you safer.
• If you can't quickly and safely get away from the coast, estuary or river mouth within 5 minutes (e.g. if you are in Southshore) then consider moving to the upper storey of a multi-storey building, or to the nearest high dune. You should aim to be at least 4 metres above sea level if you are still within two blocks of the coast.  It is unlikely the water from a tsunami created in Pegasus Bay would go higher than this.
• Stay up or inland for at least 2 hours, unless you are given the all clear to return from Civil Defence, or you can confirm (e.g. through GeoNet) that the earthquake was on land and not out to sea.
• It is YOUR responsibility to determine the best place for you and those with you to move to.
• Walk or cycle if you can, to avoid traffic jams. Only use your car if you have to move elderly people or those who can't move easily.
• You will need to use common sense to work out the best route to use from where you are.
• Be aware that if the ground shaking is strong, there may be unstable cliffs and rockfalls in hillside suburbs. Think about weather conditions.
• There will not be time to give an official warning or to sound any warning sirens for a local source tsunami in Pegasus Bay. Do not wait for an official warning, or for any sirens to sound, to evacuate.  
• There are no local tsunami warning systems in New Zealand, because the time between the tsunami being generated and it hitting the shore is too short to be able to give a warning.  Remember, it takes at least 10 minutes for GeoNet to accurately locate an earthquake, let alone whether it has created a tsunami or not.  A tsunami may have arrived at the coast near the earthquake in that time.  You do not need an official tsunami warning system for a local source tsunami - the earthquake is your tsunami warning.  Japan is the only country in the world that has attempted to have a local source tsunami warning system.  This warning system did not work effectively in the 2011 Japan tsunami - many people who waited for the official warning died, when they could have survived if they had taken the earthquake as their tsunami warning.

Regional source tsunamis

• Regional source tsunamis are tsunamis that are generated one to three hours' travel time away from the coast.  For the Pegasus Bay coast and Banks Peninsula that means tsunamis created from the east and north of the North Island and off the Fiordland coast.
• The most likely regional tsunami source for Pegasus Bay is the Hikurangi subduction zone fault, off the Wairarapa/Hawkes Bay/East Coast coast. Earthquakes are thought to happen here roughly every one or two thousand years but we don't know when the last earthquake happened.

• An earthquake on this fault will be felt in the Christchurch area as a moderate, rolling earthquake that lasts for more than a minute.
• A tsunami from this fault would likely take around 1-3 hours to reach Pegasus Bay. It is unlikely to be large here, but it may flood low lying areas. Sea heights above sea level at the time here would probably be around 1-2 metres, but there may be localised areas where it would be more than that because of the way tsunamis slosh around in Pegasus Bay.
• There may be enough time to sound warning sirens, once they are installed, for a Hikurangi subduction zone tsunami.  This is because we will know within half an hour or so where the earthquake was and GeoNet's tsunami gauges will tell us whether a tsunami has hit the east coast of the North Island.
• However, the most important warning will be the long moderate ground shaking from the earthquake. Do not wait for an official warning, or for the sirens to sound, to move inland or to higher ground.
• Stay up or inland for at least 3 hours, unless you are given the all clear to return from Civil Defence, or you can confirm (e.g. through GeoNet) that the earthquake was on land and not out to sea.
• Environment Canterbury is planning to undertake more detailed investigations into the effects of a Hikurangi subduction zone tsunami on the whole Canterbury coastline (including Kaikoura) within the next three years.

Distant source tsunamis

• Distant source tsunamis are tsunamis that are generated more than three hours' travel time away from the coast. For the Canterbury coast this means tsunamis from across the Pacific Ocean, most likely South or Central America.
• This is Pegasus Bay and Banks Peninsulas largest and most likely tsunami threat. The four largest recorded tsunamis to hit Christchurch, Pegasus Bay and Banks Peninsula – 1868, 1877, 1960 and 2010 – were all distant source tsunamis from South America.

• Distant source tsunamis take 12-15 hours to reach New Zealand, so there is time to issue warnings and evacuate people if necessary.  New Zealand receives tsunami advisories and warnings from the Pacific Tsunami Warning Center in Hawaii. Information from the PTWC is interpreted by tsunami experts in Wellington and national warnings are issued if there is a threat to New Zealand.
• You may not need to evacuate in a distant source tsunami – you may just need to stay out of the water and off the beach because of strong currents.
• If it is thought that a distant source tsunami could flood coastal land the Police and the Fire Service will evacuate coastal evacuation areas, and tsunami sirens will sound, where they are installed. 
• Information on coastal evacuation zones for Christchurch city are on the Christchurch City Council website.  These zones are currently being reviewed based on distant source tsunami modelling undertaken since the February 2011, as land has dropped in some areas.
• Coastal evacuation zones are currently being developed for Waimakariri District. Residents in Waimakariri and Hurunui districts should check with Waimakariri and Hurunui district councils to see whether they are in a coastal evacuation area.  Communities that would be evacuated include Amberley Beach, Leithfield Beach, Waikuku Beach, Woodend Beach and Pines Beach/Kairaki.  There is more information for Waimakariri District on the Waimakariri District Council website.
• Tsunami sirens will be sounded for a distant source tsunami, once they are installed.  If you hear the sirens, you must evacuate the tsunami evacuation zones for your district.  You will have several hours to evacuate. 

Where should I evacuate to?

If you live near the coast think about possible evacuation routes for local, regional and distant source tsunamis.   Practice these with your family or friends, and write them on your Household Emergency Plan. Find out if there are vulnerable people nearby who may need your help.

The best route to take will depend on where you are and the type of tsunami. If it is a distant source tsunami, where there is time for official warnings to be given, evacuation routes for Christchurch are given in the Evacuation information for coastal Christchurch brochure. Evacuation routes for beach settlements in Waimakariri and Hurunui Districts are the main roads out of the settlements. 

If you feel strong ground shaking and need to evacuate quickly, you may use the same route as for a distant source tsunami, or you may need to determine a faster route inland, to higher ground, or an upper storey of a building. It is your responsibility to work out the best route for you and those with you if you feel strong ground shaking or long moderate ground shaking.

What about the Kaikoura Canyon?

If a tsunami happens in the Kaikoura Canyon, just south of Kaikoura, it would affect the coastline immediately south of Kaikoura (South Bay, Goose Bay and Oaro), but it would be too small by the time it got to Pegasus Bay to do any damage. This is because this tsunami comes from one point (an undersea landslide), rather than an offshore earthquake fault line, so the waves created decrease very quickly from the source.

Why didn’t the September 2010 or the February, June or December 2011 earthquakes cause tsunamis?

The September 2010, February 2011 and June 2011 earthquakes did not cause tsunamis because they happened on land and did not displace the sea floor. The December 2011 earthquakes were out to sea, but the faults that moved were too small to get all the way to the surface and cut the sea floor and create a tsunami. The aftershocks from these earthquakes are also too small to cause a tsunami. An earthquake at sea usually needs to be greater than magnitude 6.5-7 for the fault to cut all the way up through the rocks to the sea floor to cause even a small tsunami.

What about a Japanese tsunami? Could we get a tsunami that big in Pegasus Bay or Banks Peninsula?

No.  The Japanese tsunami was created by a big earthquake fault just offshore of Japan called a subduction zone fault, where one tectonic plate is being pushed under another tectonic plate.  These subdution zone faults can cause very big earthquakes (magnitude 8+) and very big tsunamis, like the 2011 Japanese tsunami or the 2004 Indian Ocean tsunami.  There is a subduction zone fault off the east coast of the North Island, which could create a big tsunami there, but there is no subduction zone fault off the Canterbury coast that could create such a big tsunami here. 

Are the tsunami warning sirens for Christchurch still coming?

Christchurch City Council has confirmed a budget for tsunami warning sirens and is currently working through the process of installing them.  They should be installed by the end of June 2012.  When installed these sirens will not be used for a local tsunami because there will not be time to sound the sirens.

Sirens will only be used in the event of a distant source tsunami from across the Pacific Ocean, and possibly for a regional source tsunami from the Hikurangi subduction zone if there is time. There will not be time to sound the warning sirens if there is a local source tsunami in Pegasus Bay – earthquake shaking will be your ONLY warning.