Earthquakes
Key Messages About Earthquakes
- Everywhere in New Zealand is exposed to earthquake hazard. Large earthquakes can injure and sometimes kill people, and damage or destroy property.
- Earthquakes can also trigger other hazards such as tsunami, landslides, floods and fires.
- You can reduce the impacts of earthquakes by making sure objects that can fall, damage and hurt are either placed somewhere else, or fixed and fastened.
- Make and practise your emergency plan, have a grab bag and emergency supplies.
- Drop, Cover and Hold is the right action to take during an earthquake. It stops you being knocked over, makes you a smaller target for falling and flying objects, and protects your head, neck and vital organs.
- Practise Drop, Cover and Hold at least twice a year. You can do this when the clocks change for daylight savings and take part in New Zealand’s annual ShakeOut
- In a major earthquake, masonry and glass falls off buildings and into the streets. If you are inside, Drop, Cover and Hold – do not run outside or you risk getting hit by falling bricks or concrete and glass.
- If you are outside, move away from buildings, trees, streetlights, and power lines, then Drop, Cover and Hold. Stay there until the shaking stops.
- It is important to recognise the natural warning signs of a tsunami and remember, if an earthquake is Long or Strong, Get Gone.
- Expect aftershocks. Each time you feel one, Drop, Cover and Hold. Aftershocks can occur minutes, days, weeks, months and years following an earthquake.
What Causes Earthquakes?
An earthquake is the shaking of the surface of the Earth, caused by a sudden movement and energy within the Earth’s crust.
Earthquakes are the fracturing and release of energy usually on faults. Faults are fractures that go deep within the Earth’s crust. Tension builds along faults as the tectonic plates move.
Some large earthquakes may be preceded by a foreshock. All large earthquakes will be followed by aftershocks.
New Zealand Earthquakes
New Zealand lies on the boundary of the Pacific and Australian tectonic plates, so earthquakes happen here every day. Most are too small, too deep, or too far offshore to be noticed. However, a strong, damaging earthquake can happen at any time, and can be followed by aftershocks over months or even years.
Every year, GNS Science locates over 15,000 earthquakes in New Zealand. About 100 to 150 earthquakes per year are large enough to be felt.
Earthquakes tend to cluster in space and time. Some decades have few larger earthquakes and other decades have many more. From historic trends and records dating from the 1840s, we know that New Zealand can expect roughly one magnitude 6 earthquake every year, and one magnitude 7 every ten years. Since 1840, we have recorded one earthquake larger than magnitude 8, the M8.2 1855 Wairarapa Earthquake which caused the surface of the earth to be offset by up to 18 metres. The largest New Zealand earthquake in the past decade was the M7.8 Kaikoura earthquake in November 2016.
Clusters of earthquakes around a particular location are known as swarms and can include many quakes of varying size. If there is increased earthquake activity, the probability of a large earthquake occurring increases.
Magnitude measures the energy released by an earthquake at its source, while intensity describes the severity of earthquake shaking experienced at the surface.
While we know the locations of more than 600 large fault lines in New Zealand, there are many other faults that we don’t know about. Everywhere in New Zealand is exposed to earthquake hazard.
Learn more about New Zealand earthquakes
Earthquake Hazards
Large earthquakes can injure and sometimes kill people, and damage or destroy property and lifelines utilities. For example, the magnitude 6.3 Christchurch earthquake on 22 February 2011 caused major damage and disruption to the Canterbury region. 181 people died as a direct result of the earthquake.
Earthquake hazards include ground shaking, land deformation, and liquefaction.
- Ground shaking is the shaking of the ground during an earthquake and is one of the main causes of earthquake damage to buildings and lifeline utilities.
- Land deformation is changes to the ground surface, such as swelling, sinking, or cracking. Land deformation can damage buildings, structures and lifelines utilities, cause landslides and change the risk of flooding as the ground moves.
- Surface fault rupture is the ripping and warping of the ground surface along a fault as the ground on one side moves sideways and/or up relative to ground on the other side. This only happens in moderate to large earthquakes (larger than about magnitude 6.5) where the fault movement is large enough to come all the way up to the ground surface.
- Liquefaction is a process where loose soils below the groundwater level substantially lose strength and stiffness, in response to earthquake shaking. This causes the soil to behave like a pressurised liquid. In some cases, this soil/water mixture is ejected up to the ground surface. Liquefaction caused much damage in the Canterbury Earthquake Sequence, primarily to houses and buildings.
Earthquakes can also trigger other hazards such as tsunami, landslides, floods and fires and gas leaks.
All of these hazards can cause damage to people, the environment, buildings and lifeline utilities including transportation, water, electricity and communications networks.
Earthquakes can also have profound psychological and emotional impacts. Homes and possessions can be damaged or lost, and family life disrupted. However, there are simple fixes you can do to ensure your whare/home is as earthquake-safe as possible, and preparing your whānau/family will help keep you safe in an emergency.
Useful Links on the Get Ready Website
Drop Cover Hold
Shake Out
Grab Bag
Emergency Supplies
Long or Strong, Get Gone
