How are earthquakes caused?
The lithosphere or the crust literally floats on the mantle. The earth's surface is broken up into a number of plates called tectonic plates. Earthquakes, volcanic activity and mountain formation on land and in oceans, occur along the boundaries of these tectonic plates. The places where the tectonic plates meet are called fault lines. Earthquakes occur along these fault lines. Convection currents in the hot, molten magma below the crust make tectonic plates move constantly. Some plates slide past one another. When two plates slide past each other it produces strains on the rocks on both the sides. An earthquake results when the strain builds up and causes the rocks to break and shift. Earthquakes are the natural means of releasing stress built up in the mantle.
The earth crust works in the same way. As the plates move, they put stress on themselves and each other. When the force is large enough, the crust breaks. When the crust breaks, the stress is released. The energy moves through the earth in the form of waves called seismic waves. They move from the centre and spread outwards just like waves of water.
Earthquakes also occur where there are active volcanoes. A volcano is a mountain or hill formed by the accumulation of magma or molten rocks. Volcanoes are created when magma, which is less dense than the solid rock, pushes its way up through the earth's crust.
When earthquakes happen under the sea, they can cause a series of huge waves called tsunamis. They can cause great damage to life and property.
The earth crust works in the same way. As the plates move, they put stress on themselves and each other. When the force is large enough, the crust breaks. When the crust breaks, the stress is released. The energy moves through the earth in the form of waves called seismic waves. They move from the centre and spread outwards just like waves of water.
Earthquakes also occur where there are active volcanoes. A volcano is a mountain or hill formed by the accumulation of magma or molten rocks. Volcanoes are created when magma, which is less dense than the solid rock, pushes its way up through the earth's crust.
When earthquakes happen under the sea, they can cause a series of huge waves called tsunamis. They can cause great damage to life and property.
Detection Of Earthquakes
Seismologists, or earthquake scientists, measure the strength of an earthquake by estimating the amount of energy released at the focus. The focus is the point of origin of an earthquake. Seismic waves are detected, recorded and measured by sensitive instruments called seismographs. The movement is recorded on a seismogram. The epicentre is the point on the earth's surface directly over the focus.
Human Activities Also Cause Earthquakes
Earthquakes also occur due to man's activities like conducting underground nuclear tests, mining, building of dams and filling reservoirs behind dams.
What You Should Do During Earthquakes
If you live in a high-risk area, you must always have an emergency kit ready. It should contain a torch with extra batteries, first-aid material, food, water and money.
During an earthquakes, stay away from windows. If you are outside a building, stand in an open area away from buildings and trees, which may fall. If you are not in a position to get out into the open, take shelter under a table, if possible. This will protect you from falling objects on you. If you are in a car, stop the car and stay inside it. After the earthquake is over, be careful about entering a building and watch out for falling objects. Put out any fire and help in removing the injured for first-aid. Listen to the radio for any instructions that might follow after the earthquake.
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