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earthquakes

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Anilkumar S.S

Register No: 13983004

Social Science Option

KUCTE Nedumangadu

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• The processes that take place in the interior of the earth causes in the storage of energy in some portions in the earth. Earthquakes occur on those instances when these energy is being released. The point of origin of the earthquakes is known as focus and the point just above the focus on the surface of the earth is known as epicenter.

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The energy being released from the focus propagates as waves. These cause tremors on the surface of the earth and cause destruction.

• The instrument used to measure to magnitude of the earthquake is called a seismograph. The intensity of the earthquake is measured based on the Richer Scale

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Richer Scale Effects

1 - 3 We don`t feel the tremors. But recorded in the seismograph

3 - 4 Tremors felt

4 - 5 Small objects fall, doors and windows shake.

5 - 6 Damage to weak buildings

6 - 7 There is strong tremor over vast areas, weak buildings collapse.

7 - 8 Comparatively strong earthquake, there is a lot of destruction over large areas, strong buildings collapse, tsunamis caused.

8 - 9 Severe earthquake, causes destruction in more than 100 kilometre circumference, cause strong tsunamis (like the 2004 tsunami in the Indian Ocean)

9 and above Very intense earthquake, very rare.

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Primary waves move very fast through solids, and very slowly through liquids. These waves reach the epicenter from the focus first. But secondary waves move only through solids. They do not travel through liquids. These reach the epicenter following the primary waves. These two waves travel to interior of the earth . So they are known as body waves. Depending on the density of the material they pass through, there is a difference in their speed. Waves the material traversed is more dense, the speed is more and where the density less, the speed is also less,. According to the density, the direction of the waves change . Surface waves reach the epicenter last. They through the surface of the earth and cause destruction on the earth`s surface.

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