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• There are a number of hazards caused by plate tectonics including earthquakes and tsunamis.
• Earthquakes have both primary effects (such as the destruction of buildings) and secondary effects (such as fires, water contamination, or spread of diseases) .
• There are ways of reducing the effects of earthquakes by, for example, planning, predicting and preparing.

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An earthquake is a sudden, violent shaking of the ground. An earthquake occurs when two tectonic plates push together. The pressure of these colliding plates builds up inside the Earth’s crust. The point in the crust where the pressure is released is called the focus. The point on the Earth's surface above the focus is called the epicentre. When the pressure is too much it is suddenly released and waves of energy, called seismic waves, occur. These seismic waves travel through the earth causing it to shake.

Find out more about tectonic plates.

The shaking of the ground caused by an earthquake can cause a variety of effects. These can be classed as primary or secondary effects. Primary effects are caused by the earthquake itself, whereas the secondary effects are caused by the primary effects.

• Buildings may collapse due to the shaking of the ground.
• People may die if they are inside a building when it collapses.
• Roads may be blocked, gas and water pipes could be broken and electricity could be cut off.

• The cost of rebuilding may be high.
• Trade will decrease, especially if the infrastructure (roads, airports etc) have been damaged.
• Spread of diseases may rise. If dead bodies are left in the open for a long period of time they can cause a risk of infectious diseases, such as tuberculosis and hepatitis B.
• Poor sanitation may occur if water pipes were broken during the earthquake.

Earthquakes at sea cause water to be displaced, creating a fast-moving wave that spreads out in all directions. In the deep ocean, tsunami waves can reach speeds of up to 800 kilometres per hour. As the wave approaches shallower waters near to the shore, its speed will decrease but the waves will become higher.

These waves cause flooding and the majority of the deaths associated from tsunamis are caused by drowning. The flooding can contaminate water supplies and cause the destruction of homes.

The flooding can also lead to secondary effects such as causing illnesses in the area. These illnesses are due to poor sanitation and lack of clean water because of contaminated water supplies due to flooding. Flooding washes into clean water supplies carrying debris and sewage.

• A sudden shift in plate movement causes water displacement at the epicentre.
• Large waves move along the seabed away from the epicentre.
• As the waves move from deep water to shallow water near the coastal area, they increase in height and break.

After an earthquake the affected country must respond. Some responses will happen very quickly (immediate responses) and some may go on for months or years (long-term responses).

Immediate:

• People are rescued from destroyed buildings.
• People are evacuated.
• Emergency shelters are put in place.

Long-term:

• Reconstruction of destroyed buildings will take place.
• Infrastructure such as roads repaired.
• Temporary housing is provided.

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Countries can try to reduce the risk of damage from earthquakes by attempting to predict when they might occur, protecting their buildings to make them earthquake proof and preparing their population for what to do in the event of an earthquake.

Prediction

It is impossible to predict with certainty when an earthquake will happen but scientists can try in a number of ways. Using historical records GPS and seismographs to measure small tremors scientists can predict where they believe earthquakes will occur. There has been some evidence that monitoring changes in animal behaviour could be a way to predict imminent earthquakes and seismologists in China have monitoring stations in zoos for this reason.

Protection

The most effective way to reduce risks is earthquake protection. Buildings can be constructed to resist the shaking associated with earthquakes. This can be done with counterweights that correct the movement of the building and cross-bracing to reinforce the structure, as shown in the image below.

Preparation

By training people what to do in the event of an earthquake, countries can increase the chances of survival in the event of an earthquake. This can be in the form of earthquake drills in schools or training emergency services on how to respond.

Natural hazards, such as earthquakes, can cause more damage in low incomes countries (LICs) than in high income countries (HICs).

HICs may have invested money and training into preparing the citizens of a country in evacuation methods, as well as increasing the stability of buildings and being able to invest in earthquake precautions when constructing new buildings.

However, LICs are less likely to have the money and resources to prepare for these natural hazards. Therefore when the hazard strikes, they are greatly affected. An example of this is the 2010 Haiti Earthquake that killed over 200,000 people, largely due to weak buildings collapsing.