Below are revision notes for earthquakes. If you require more detailed information take a look at the earthquakes geotopic.
Earthquakes are caused by sudden movements of the earth's crust releasing seismic waves. The focus of an earthquake is the point where an earthquake occurs underground. Shock waves move out from the focus. The point on the earth's surface directly above the focus is known as the epicentre.
The Richter Scale and Mercalli scale are used to measure the effects of earthquakes. The Richter Scale measures the strength of an earthquake on a 1-10 scale. The scale is logarithmic, the strength of an earthquake increases by 10 every point you go up the scale. For example an earthquake measuring 6 is 10 times stronger than one that measures 5. The Mercalli scale measures the physical effects of an earthquake on a scale of 1-12.
Earthquakes in LEDCs usually result in a greater loss of life than those of similar strength in MEDCs. This is due to poorer quality buildings and less efficient emergency services. The economic cost of earthquakes is usually higher in MEDCs.
Factors that affect the impact of earthquakes include the proximity of the epicentre to urban areas, the time of day, the strength of the earthquake, the level of economic development of an area, the population density and the time of year.
A range of attempts to reduce the impact of earthquakes has been attempted. These range from more accurate earthquake prediction, improved early warning systems, building solutions (e.g. use of seismic isolators under buildings in Japan) and improved evacuation procedures.
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