Stirred and shaken

Recently, a major earthquake hit Nepal leaving behind destruction and devastation. Why and how did this happen?

Published - June 18, 2015 08:01 pm IST

Nature's Fury: The after effects of an earthquake.

Nature's Fury: The after effects of an earthquake.

Have you seen things rattle on top of the table or falling off shelves? Have you been asked to run out to open spaces? This is how it feels when there is an earthquake. In simple terms, tremors on the earth’s surface when two rocks slide past each other.

To understand earthquakes, you have to study the formation of the earth. The earth is made up of four layers and the top of the mantle and the crust make up a thin sheet on the earth’s surface. This sheet is broken down into several pieces or plates.

Stronger push

We think the earth is stationary but, in actual fact it is constantly moving. The plates move in sync with each other but sometimes they collide. Energy is essential for the movement of the plates. Let’s compare the earth’s plates to a jigsaw where several big and small pieces placed correctly make up the game. But if two uneven pieces get stuck, the force used to get them out will break the pieces.

Similarly, as the earth’s plates move and shift, there is a crack on the surface of the earth called “Fault Line”. Many faults can be noticed along the plate edges. As the plates move, the rough edges are bound to stick together along the fault while the rest of the plate is still in motion. Hence energy is stored up and this creates more pressure. All of a sudden, the stuck plates free themselves. As a result, the pent up energy called seismic waves release through the fault in all directions. These waves vibrate as they travel through the earth and the moment they touch the earth’s surface, they cause destruction.

Recent quakes

The constant bumping of the plates caused the devastating earthquake in Nepal on April 25, 2015. The Indian plate continues to move northward beneath the Eurasian plate at 45mm a year. Nepal stands on the fault called “Thrust Fault” where a sudden release of energy along the fault resulted in one plate jumping on the other. The earthquake measured 7.9 magnitude, with an aftershock of 6.7 magnitude the next day. Aftershocks caused landslides on Mount Everest. Besides, tremors were felt across the Indian states — New Delhi, Bihar, Uttar Pradesh, Assam, West Bengal, Sikkim, Odisha, Uttarakhand and Gujarat including the southern states of Andhra Pradesh, Kerala and Karnataka. Bangladesh, Southwest China and Pakistan felt tremors as well. Another quake of 7.3 magnitude hit Nepal on May 12, 2015 causing more damage. Parts of India felt the aftershocks with Delhi measuring a magnitude of 6.2.

Cause and Effect

Seismic zone classification determines the effects of the quakes in terms of their intensity. India is divided into seismic zones II to V. Zone I, a damage free zone was merged into zone II.

Zone II – Known as the least active seismic zone, earthquakes occur with an intensity of 5 to 6.

Zone III – When a force of 7 leads to moderate damage.

Zone IV – Intensity of 8 leading to major damage.

Zone V – Also called danger zone, a lot of devastation takes place when the intensity goes as high as 9 and up.

To know more : >

Plate collision and mountain ranges

The Himalayas is a perfect example of this. The process of the world’s biggest mountain range started 200 million years ago when only a single supercontinent called “Pangea” existed. Pangea eventually split to form two major continents — Laurasia and Gondwanaland.

While Laurasia split into North America along with Europe and Asia (Eurasia, a landmass on the Eurasian plate); Gondwanaland spilt to Antarctica, Australia and South America. The Indian subcontinent, a landmass on the Indian plate was a part of Gondwanaland. The forces in the earth’s mantle caused the drift. The Indian subcontinent drifted as well, moved northwards, collided with the Eurasian plate to form the Himalayas and closed an entire ocean.

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