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Earth's structure

The earth has four layers – the crust, the mantle, the outer and the inner cores.

Tectonic plates

Tectonic plates are very thick and as far as scientists know they do not break.

Our plate boundary

New Zealand lies on the boundary of the Pacific and Australian plate boundary and how these two places meet and interact changes. For example, off the East Coast of the North Island lies the Hikurangi Subduction Zone. Here the Pacific Plate is subducting and slowly moving under the Australian Plate. Through most of the South Island, the two plates grind past and into each other along the Alpine Fault. At the southern end of the South Island, the Australian Plate subducts under the Pacific Plate at the Puysegur Trench.

Tectonic plates move because they are floating on top of hot liquid rock (called the mantle) under the earth’s crust. Big swirls of moving liquid rock jostle the tectonic plates on top and make them move.

Yes. New Zealand is intersected by two tectonic plates – the Pacific and the Australian plates. As these plates continue to move past and into each other, New Zealand’s landscape will continue to change.

A trench is created where one tectonic plate subducts under another tectonic plate. A fault line is a crack in the upper layer of the Earth’s crust. This fault is caused by stress caused by the tectonic plate movements

Hikurangi subduction zone

Not sure! Perhaps in respect of our maunga Hikurangi

The Hikurangi Trench was created by the Pacific tectonic plate subducting under the Australian tectonic plate. The ocean plate (the Pacific Plate) is being pushed (converged) under the thicker Australian continent plate and as it is forced underneath it creates a big gully called a trench. Because it is near land, this gully fills up with rubble (sand and silt – called sediment) and is quite shallow.

 

It depends where you travel from, in some places the trench is close to shore and in other places it is further away.

The Hikurangi Trench is 2.5 – 4 kms deep. It runs from Kaikoura in the South to Tonga in the North.

Tectonic plates are quite a new idea (first ‘discovered’ in the 1960s). There is a lot that scientists would like to know about how they move and work. As well it is good to have a lot of information about hazards (like earthquakes and tsunami) so we can be prepared. Scientists think that some earthquakes at tectonic boundaries can be “mega-quakes” so the more we know about the Hikurangi Trench the better prepared we are for a big earthquake and possible tsunami.

 

Earthquakes

Earthquakes are caused by faults or tectonic plate boundaries moving.

There is an estimated 50-80 earthquakes every day in New Zealand. Most cannot be felt.

Around 20,000 every year. Most of the time, they cannot be felt by us.

Earthquakes usually last 10 – 30 seconds. However, during the very largest earthquakes, the rupture can continue for up to 5 minutes. For these earthquakes very high levels of aftershocks mean that continuous ground shaking can be felt for hours.

No. Earthquakes are only felt on the ground.

Animals are a lot more sensitive to the earth and the movements of it than humans.

The shaking of the ground will move objects within the house. A strong quake can knock TVs and cabinets over, open drawers and cupboards. The movement of the ground makes building sway and shake and if they are not built properly, will break and fall.

Not from the earthquake itself – it’s more from falling objects, buildings, landslides etc

Dam’s usually are engineered to withstand a certain amount of shaking and so it is likely something like that would have to go through a thorough risk review process to access the levels of risk

There is no evidence to suggest large amounts of water cause earthquakes. However, large amounts of water immediately before or after a large earthquake, for example a weather event, could increase the likelihood of secondary hazards, such as landslides and flooding.

 

The waves travel at different speeds. P waves travel at about 20,000 km an hour -this is 20 times faster than a jet aircraft. They usually cause very little damage. S waves travel at about 10,000km an hour and cause the main rolling and side to side motion. These waves cause the most damage to buildings

Tsunami

Evacuate. This can mean a tsunami is coming.

If the tsunami is coming from Hikurangi the only warning will be a strong earthquake (hard to stand up in), a long earthquake (a minute or more), you see the ocean recede or you hear very loud noises coming from the sea. If the tsunami is coming from Chile there will be plenty of warning and you will be evacuated by Civil Defence.

Tsunamis are caused by sudden movement under the ocean. These can be from an underwater volcanic eruption, and underwater landslide or an underwater earthquake.

‘Tsunami’ is the Japanese word for ‘Harbour Wave’ and Japan has had many tsunamis in its history.

We may feel a long or strong earthquake.

A tsunami travels up to 1000km/hr an hour at deep sea, but slows to 30 km/hr as it hits land. But with the force of the wave traveling 1000km/hour behind it! The sea becoming shallower and the force of the water behind is why a tsunami wave gets higher as it approaches land, and in a really big tsunami can become like a wall of water.

A tsunami is a series of waves, so you could get several waves coming minutes or hours apart from each other.

In deep water the wave is only a metre or so high, but most of the energy from the wave is underwater, so there can be strong currents.

Tsunami travel away from the source of the tsunami in all directions. However when they hit the East Coast, they are coming from the east – most likely from either the Hikurangi Trench, the Kermadec Trench, or Chile.

The largest recorded tsunami was in 1958 in Alaska. An earthquake generated an enormous landslide which crashed into the ocean creating a wave that destroyed vegetation over 500 metres above sea level.

In New Zealand, the 1931 Hawke’s Bay earthquake triggered a landslip at Waikare which in turn caused a localised 15.3 metre tsunami. At Napier there was a tsunami of about 3 metres. Otherwise the largest recorded tsunami in NZ was in Gisborne in 1947 and it was 10 metres.

A tsunami will stop when it runs out of energy.

Strong swimmers like sea lions, fish and dolphins often respond quickly to a tsunami and swim safely to deeper water. Birds can be very vulnerable in a tsunami, especially if they are nesting near the coast. The ecosystem after a tsunami can be altered due to soil being deposited into the sea as the waves recede, and saltwater being deposited onto the land as the waves come inland. Sometimes this is bad for the animals, but sometimes it is good – dead and decaying material in the sea leads to a growth in plankton, which increases fish species, which in turn increases the dolphin population. Nature has a way of adapting and surviving natural events, but some ecosystems and animals may need extra care from people to help them recover.

When they are in deep water yes – but if they are close to land and it is a large tsunami, they will probably be swept on to land with the force of the water.

No. The best thing we can do is to be prepared and well educated on what we can do to look after ourselves and our families.

It’s really the other way round – tsunamis are created by the displacement of large amounts of water due to underwater landslides and earthquakes. When a tsunami reaches land, the speed and force of the water can dislodge large amounts of soil, therefore creating landslides.

Volcanoes

New Zealand is part of, what is known as, the Ring of Fire. This is where 90% of all the world’s earthquakes occur, 75% of all the world’s volcanic eruptions occur and 80% of all tsunami occur.

It’s really unlikely that Lake Taupō will erupt anytime soon

How to prepare

The most important thing would be to

1. Make a plan with family and friends

2. Practice your Drop Cover Hold and if you are near the coast practice your tsunami evacuation hikoi

3. Have food and water supplies (if you personal circumstances allow)

 

Scientists

A scientist is a person who organises what we already know about the world, and then learns more about the world by asking who, what, where, when and why questions. Scientists who study earthquakes and tsunami are called earth scientists. An earth scientist who specifically studies earthquake waves is called a seismologist, while an earth scientist who studies rocks is called a geologist. Geology is the study of rocks and the earth.

Scientist love to learn about things. They are interested in the world and how it works. A smart scientist has a lot of questions and ideas they would like to investigate – some of their ideas can be quite crazy and this can make them great scientist! But really anyone can be a scientist. Science is just pursuing your curiosity.

A student might work as a scientist for free, as part of their study. However, a qualified geologist can earn up to $130 000 a year. There is a shortage of geologists in New Zealand so it is a good field to get into to!

Everything from biology, space, our history, fossils and artefacts, microbiology, engineering, physics and chemistry.

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