Introduction to Earthquake

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Internal Structure of Earth

Earth consists of many different layers. The innermost layer is the hot solid inner core followed by liquid outer core, mantle and finally the crust. This is the layer on which we live.

Even though it seems to be a single layer, the complete crust is made up of many parts called tectonic plates that are joined together. These plates are not stationary but are continuously moving.

When the plates collide head-on, they push each other up above the surface. This is how mountains are formed. For example, the collision between the Eurasian Plate and the Indian plate resulted in the Himalayas.

What is an Earthquake?

An Earthquake is a sudden shaking or trembling of the earth which lasts for a very short time.

How Does an Earthquake Occur?

An earthquake is the result of the collision or sliding of the earth’s tectonic plates.

 These plates keep moving relative to one another all the time. But because these movements are very mild, very weak waves are produced. Thus we don’t experience earthquakes frequently.

But if the movement of plates is very aggressive, it may lead to strong waves generated from the point where the plates collide or slide past each other. This results in a severe movement or shakes, which we call ‘Earthquakes’.

What is the Focus and Epicentre of an Earthquake?

The point where the quake originates in the earth’s crust is called the Focus. And the point

on the earth’s surface exactly above the focus is called Epicentre.

 What are Seismic Zones?

Earthquakes cannot be predicted. But with Seismology, that is the study of earthquakes, various areas on earth have been identified that are more prone to earthquakes. These are called the Seismic zones or Fault zones.

Seismic zones are situated at the boundaries of the tectonic plates.

For example, in India, the Western and Central Himalayas along with Kashmir, the North eastern region and the north western regions like Rajasthan and the Rann of Kutch come under the seismic zones.

 How is the severity of an earthquake measured?

The intensity or severity of the earthquake is calculated with the help of an instrument called a Seismograph. It is expressed in terms of magnitude on a particular scale called the Richter scale.

An earthquake of intensity close to 7 on the Richter scale is usually considered severe. For example, the earthquake in Bhuj, Gujarat that occurred on January 26, 2001, had a magnitude greater than 7.5.

Summary

Did you know?

The most intense earthquake ever recorded was in Valdivia, Chile, on May 22, 1960. It measured 9.5 on the Richter scale.