Why and How of the earthquake - Indian fault line

"The reason is the regular movement of the fault line that runs along Nepal’s southern border, where the Indian subcontinent collided with the Eurasia plate 40 million to 50 million years ago."

But why? To know continue reading...

As the plates push against each other, friction generates stress and energy that builds until the crust ruptures. In the case of a quake, the plate jumped forward about 2 meters, or 6.5 feet. Such quakes tend to cause more damage and more aftershocks than those that occur deeper below the earth’s surface. After an earthquake, the plates resume moving and the clock resets. 

Earthquakes dissipate energy, like lifting the lid off a pot of boiling water, but it builds back up after you put the lid back on.

Nepal is prone to destructive earthquakes, not only because of the massive forces involved in the tectonic collision, but also because of the type of fault line the country sits on. Normal faults create space when the ground cracks and separates. Nepal lies on a so-called thrust fault, where one tectonic plate forces itself on top of another.

The most visible result of this is the Himalayan mountain range. The fault runs along the 1,400-mile range, and the constant collision of the India and Eurasia plates pushes up the height of the peaks by about a centimeter each year.

Despite the seeming regularity of severe earthquakes in Nepal, it isn’t possible to predict when one will happen. Historic records and modern measurements of tectonic plate movement show that if the pressure builds in the region in a way that is “generally consistent and homogeneous,” the region should expect a severe earthquake every four to five decades.

The earth’s tectonics plates are constantly in motion. Some faults release built-up stress in the form of earthquakes. Others release that energy quietly.

All we need to know:

What is an earthquake and what causes them to happen?

An earthquake is caused by a sudden slip on a fault. Stresses in the earth's outer layer push the sides of the fault together. Stress builds up and the rocks slips suddenly, releasing energy in waves that travel through the earth's crust and cause the shaking that we feel during an earthquake. An earthquake occurs when plates grind and scrape against each other.

What is a fault?

Faults are fractures in Earth's crust where rocks on either side of the crack have slid past each other. Sometimes the cracks are tiny, as thin as hair, with barely noticeable movement between the rock layers. But faults can also be hundreds of miles long.

At what depth do earthquakes occur?

Earthquakes occur in the crust or upper mantle, which ranges from the earth's surface to about 800 kilometers deep (about 500 miles).

What is "surface rupture" in an earthquake?

Surface rupture occurs when movement on a fault deep within the earth breaks through to the surface. Not all earthquakes result in surface rupture.

How are earthquakes measured?

The familiar Richter scale (which is not a physical device but rather a mathematical formula) is no longer widely used by scientists to report an earthquake's size. Today, an earthquake's size is typically reported simply by its magnitude, which is a measure of the size of the earthquake's source, where the ground began shaking. 

While there are many modern scales used to calculate the magnitude, the most common is the moment magnitude, which allows for more precise measurements of large earthquakes than the Richter scale. 

A network of geological monitoring stations, each with instruments that measure how much the ground shakes over time called seismographs allow scientists to calculate an earthquake's time, location and magnitude. 

Seismographs record a zigzag trace that shows how the ground shakes beneath the instrument. Sensitive seismographs, which greatly magnify these ground motions, can detect strong earthquakes from sources anywhere in the world.

How are quakes classified?

Based on their magnitude, quakes are assigned to a class. An increase in one number, say from 5.5 to 6.5, means that a quake's magnitude is 10 times as great. The classes are as follows:

Great: Magnitude is greater than or equal to 8.0. A magnitude-8.0 earthquake is capable of tremendous damage.
Major: Magnitude in the rage of 7.0 to 7.9. A magnitude-7.0 earthquake is a major earthquake that is capable of widespread, heavy damage.
Strong: Magnitude in the rage of 6.0 to 6.9. A magnitude-6.0 quake can cause severe damage.
Moderate: Magnitude in the rage of 5.0 to 5.9. A magnitude-5.0 quake can cause considerable damage.
Light: Magnitude in the rage of 4.0 to 4.9. A magnitude-4.0 quake is capable of moderate damage.
Minor: Magnitude in the rage of 3.0 to 3.9.
Micro: Magnitude less than-3.0. Quakes between 2.5 and 3.0 are the smallest generally felt by people.

What are the seismic zones of India?

The Geological Survey of India (GSI.) first published the seismic zoning map of the country in the year 1935. With numerous modifications made afterwards, this map was initially based on the amount of damage suffered by the different regions of India because of earthquakes. Color coded in different shades of the color red, this map shows the four distinct seismic zones of India. Following are the varied seismic zones of the nation, which are prominently shown in the map:
Zone - II: This is said to be the least active seismic zone
Zone - III: It is included in the moderate seismic zone
Zone - IV: This is considered to be the high seismic zone
Zone - V: It is the highest seismic zone

Designing a Safe house in an Earthquake prone area:

Government has already provided the guidelines to construct houses in accordance with the seismic zones of India. Please go through the below link:

How to cope with an Earthquake: