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Earthquakes occur when tension is released from inside the crust. Plates do not always move smoothly alongside each other and sometimes get stuck. When this happens pressure builds up. When this pressure is eventually released, an earthquake tends to occur.
The effects of an earthquake can be devastating - they can destroy settlements, change landscapes, and cause many deaths.
Earthquake energy is released in seismic waves. These waves spread out from the focus. The waves are felt most strongly at the epicentre, becoming less strong as they travel further away. The most severe damage caused by an earthquake will happen close to the epicentre.
Earthquake energy is released in seismic waves. These waves spread out from the focus. The waves are felt most strongly at the epicentre, becoming less strong as they travel further away.
|Type of wave||longitudinal||transverse|
|What can they travel through?||solids and liquids||solids only|
P-waves are longitudinal waves like sound waves, and s-waves are transverse waves like light waves.
The most severe damage caused by an earthquake will happen close to the epicentre.
Scientists have tried many different ways of predicting earthquakes, but none have been successful. One basic idea behind quake prediction is that faults send out subtle but detectable warnings before they slip. Scientists have looked at a host of potential warning signals, or "precursors," including foreshocks, weird animal behavior, and changes in the water table, stream flow, well levels, and patterns of electrical currents in the ground. However, on any particular fault, scientists know there will be another earthquake sometime in the future, but they have no way of telling when it will happen.
Earthquakes can destroy settlements and kill many people. Effects of earthquakes are often classified as primary and secondary impacts. Primary effects occur as a direct result of the ground shaking, eg buildings collapsing. Secondary effects occur as a result of the primary effects, eg tsunamis or fires due to ruptured gas mains. It is also possible to classify the impacts of an earthquake by taking the following factors into account:
|Social impacts||Economic impacts||Environmental impacts|
|Short-term (immediate) impacts||People may be killed or injured. Homes may be destroyed. Transport and communication links may be disrupted. Water pipes may burst and water supplies may be contaminated.||Shops and business may be destroyed. Looting may take place. The damage to transport and communication links can make trade difficult.||The built landscape may be destroyed. Fires can spread due to gas pipe explosions. Fires can damage areas of woodland. Landslides may occur. Tsunamis may cause flooding in coastal areas.|
|Long-term impacts||Disease may spread. People may have to be re-housed, sometimes in refugee camps.||The cost of rebuilding a settlement is high. Investment in the area may be focused only on repairing the damage caused by the earthquake. Income could be lost.||Important natural and human landmarks may be lost.|
The size of an earthquake is measured on a Richter scale 0-10 of magnitude using an instrument called a "seismograph". Seismographs are basically pens suspended over a paper-covered rotating drum. When the earth trembles the pen makes a larger squiggle on the drum, allowing the size of the shaking to be measured. Each whole number on the Richter scale represents an earthquake 30 times larger than the number below it. Earthquakes that measure less than 3.0 are not usually felt, while one of 5.0 produces the same amount of energy as the Hiroshima atomic bomb. Earthquakes measuring around 7 or 8 on the Richter scale can be devastating. The largest recorded quake happened in Chile in 1960 and measured 9.5.
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BEFORE AN EARTHQUAKE:
DURING AN EARTHQUAKE:
AFTER THE SHAKING STOPS:
Why do earthquakes occur? Learn about them in this activity!
Understand how seismic waves work by playing the following activity!
Play the following game to understand more about seismic waves!
At 4:53 pm on January 12 2010, the worst earthquake to hit the Caribbean in 200 years struck the impoverished nation of Haiti. The epicentre of the 7.0-magnitude earthquake was only 25 kilometres from the country’s capital, Port-au-Prince. The damage was massive and immediate, with the death toll to reach 230,000.
What decisions would you make as an earthquake survivor, aid worker, or journalist in Haiti after the earthquake? Inside the Haiti Earthquake is a first-person simulation based on documentary footage from Haiti and real-life decision scenarios. Try it now below to obtain your first hand experience about the devastating earthquake.