Earthquakes

EARTHQUAKES
  • A sudden movement of Earth’s crust (or) a motion of the ground surface is known as earthquake.
  • Earth’s crust has many tectonic plates of solid rock which slowly move along their boundaries.
  • Hypocenter is a point of sudden energy release.
  • Epicenter is the place on the ground surface (fault lines or planes of weakness) recording seismic waves (first movement) for the first time.
  • The intensity of energy released by an earthquake is measured by the Richter scale devised by Charles F. Richter.
  • Sesimometer is an instrument used to measure seismic waves.

Earthquake

Severity of an earthquake

S.No

Richter Scale

Severity of Earth quake

1.

Less than 4

Insignificant

2.

4-4.9

Minor

3.

5-5.9

Damaging

4.

6-6.9

Destructive

5.

7-7.9

Major

6.

More than 8.9

Great

Tusnamis-(High Sea waves) (Japanese word)

  • Severe earthquakes under sea water generate high sea waves and these are referred to as tsunami in Japanese language. They travel at a speed up to 1000mk/hr or more. They rise from 15 meters to 65 meters in height at sea shore, causing vast devastation in coastal areas.
  • The first Tsunami hit India in 1945, when Indians were engaged in the war of Independence. At that time, people did not worry about Tsunami much. Even now there is a danger of Tsunami in the Arabian sea. People are not aware of this danger. But the animals are capable of learning the tsunami strike in advance with the help of their ultrasonic radiation. Thus, they often escape from the danger. Therefore, it is better to train sea animals as done in China, in order to caution the human beings about tsunami in advance. A tsunami-warning instrument is to be fixed in the Bay of Bengal to track tsunami in advance.
  • Generally tsunami strikes during the beginning or towards the end of a month. For example, tsunamis struck on 27th August 1883, 25th November 1945 and 26th December 2004. In some countries, tsunami struck in the beginning of the month.

Case studies

  • Earthquake on 26-12-04 with 9 Richer scaler occurred under sea near Sumatra in Indonesia and it created tsunami waves to a height of 10m in India (Tamil Nadu), Malaysia, Thailand and Andaman island. About 2.5 lakhs of people died due to tsunami waves.
  • In TamilNadu , tsunami caused death and destruction in the low-lying areas near sea shore from Chennai to Kanyakumari.
  • In China, 8,30,000 people in the year 1556 and 50,000 people in the year 1976 died of tsunami.

Causes

  • Natural factors: Friction due to moving of tectonic plates creates stress which leads to fractures and causes earthquakes.
  • Human factors:
    • Underground nuclear testing causes earth tremor.
    • Collection of huge amount of water behind a dam also causes earthquake.
    • Pouring liquid wastes into deeper wells creates tremor.

Effects

  • Earthquake causes damage to buildings, roads, factories, dams and bridges.
  • Water supply and electricity supply and Telecommunication are completely disrupted.
  • In hilly areas, land slides occur damaging dams and causing floods

Mitigation of earthquakes

  • By constructing earthquake resistant buildings or by making pads or floats beneath the buildings we can reduce the impact of earthquake.
  • By making wooden houses in seismic zones, the effects of earthquake can be mitigated.  
Last modified: Thursday, 4 August 2011, 9:20 AM