4. An Earthquake is a sudden shake of the Earth's crust.The vibrations may vary in magnitude.The magnitude of an earthquake is measured on the richter scale. The underground point of origin of the earthquake is called the " focus ". The point directly above the focus on the surface is called the" epicentre ". Siesmologists are earthquake scientists,measure the strength of an earthquake by estimating the amount of energy released at the focus. Earthquakes by themselves rarely kill people or wildlife. It is usually the secondary events that they trigger, such as building collapse, fires, tsunamis (seismic sea waves) and volcanoes, that are actually the human disaster. As many of these could be avoided by better construction, safety systems, early warning and evaluation planning. Seismic waves are detected, recorded and measured by seismographs . Earthquakes are caused by the discharge of accumulated along geologic faults. EARTHQUAKE
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