The Andaman and Nicobar islands were jolted by an earthquake measuring 6.5 on the Richter scale, on 21st March 2014, but chances of Tsunami are ruled out by the government.

The epicentre of the earthquake was 70 Km East of Indira Point at 7:11 pm.

The earthquake events are scaled either according to the magnitude (i.e. Richter scale) or intensity (i.e. Mercalli scale) of the shockwaves.

**About Richter scale
**

The magnitude scale is known as the Richter scale (invented by Charles. F Richter) and is related to the energy released during the earthquake. The magnitude is expressed in absolute numbers i.e. 0 to 10.

Richter scale is widely used for measuring earthquakes using device called seismographs.

The Richter scale magnitude are based on a logarithmic scale (base 10).

This means that for each whole number one goes up on the Richter scale, the amplitude of the ground motion recorded by seismograph goes up 10 times.

Example – Using this scale, a magnitude 5 earthquake would result 10 times the level of ground shaking than that of a magnitude 4 Earthquake. Also in this case the energy released would be 32 times.

**About Mercalli scale
**

The intensity scale is named after Mercalli, an Italian seismologist (seismologist – is a person who studies earthquake waves propagation through the earth).

The intensity scale takes into account the visible damage caused by the earthquake the range of the intensity scale is from 1 (not felt) – 12 (total destruction). i.e. Mercalli scale measures the *effects* of an earthquake,

**What is Focus?
**

Focus is the point inside the earth’s surface which is due to sharp break in the crustal rocks causing release of energy in all directions producing shock waves.

**What is Epicentre?
**

Epicentre is the nearest tangential point to the focus on the surface, which first experiences the shock waves.

Note: Normally, the earthquake takes place around 5 km below the ground surface. The earthquake tremors can be felt upto 400 km. There are also tremors associated with underground blasts for military or mining purpose. But these are not earthquakes, as blasts occur only at 0.5 km of depth and these tremors also have a very limited reach. |