After recently when India’s northern parts, Bikaner, and Hyderabad were shaken up by the tremors caused by an earthquake, it has been deduced by the Government of India that 59% of India is prone to earthquakes. Moreover, the country’s 11% area falls under the most seismically active zones. These data are indeed worrisome and makes it all the more important to know the hows and whys related to an earthquake. In this article, we are going to crack down on the most important aspects related to an earthquake.
How to explain an earthquake?
- Well, in simple words an earthquake can be explained as a phenomenon when two flat sides of the earth surface glide away from each other.
- The surface where the gliding occurs is called the fault plane normally called the fault.
- Below the fault plane, there is a region where the earthquake starts called the hypocenter.
- A very commonly heard term while learning about an earthquake is the epicentre and is just above the hypocenter on the surface of the earth.
- An earthquake has its phases, these phases are known as foreshocks, mainshocks and aftershocks.
- A foreshock can be explained as a smaller earthquake that precedes the larger and the main earthquake and occurs at the same place.
- Aftershocks occur after the mainshock, these are also smaller earthquakes but based on the intensity of the mainshock it can go on for weeks, months and even years.
- So far the largest aftershock recorded is of the Sumatra Earthquake of 26th December 2004.
How is an earthquake caused?
Under the above heading, we learnt what causes an earthquake. Now, let’s learn what leads to the gliding of the earth surface and eventually an earthquake.
- There are four layers to the earth, from the inside to the outside these are the inner core, outer core, mantle and crust.
- Out of these layers, the crust and the outer layer of the mantle make up the skin of the earth.
- Unlike ours, the earth’s skin is not all in one piece, it is made of many pieces called tectonic plates that keep moving, sometimes sliding, and striking each other.
- The edges of the tectonic plates, technically called the plate boundaries, are said to be rough due to which they collide and get stuck while the rest of the plates keep moving.
- When the plates have moved far enough the edges get unstuck and this causes an earthquake.
Why does an earthquake shake the Earth?
- When the edges of the tectonic plates are stuck with one another, the energy that causes the plates to glide away from each other is being stocked.
- Now, when the plates have moved far enough and the edges unstuck the energy is released and it gets radiated towards the outside in all directions.
- The discharged energy comes out in the form of waves called seismic waves.
- These seismic waves shake the earth wherever it runs.
How is an earthquake recorded & measured?
- The size of an earthquake or its magnitude is based on the size of the fault and sliding on the fault, present on the plate boundaries, around which most of the earthquakes occur in the world.
- To measure the magnitude, scientists use an instrument called the seismograph and the recordings are called seismograms.
- A seismograph has a base that is set on the ground with an above-hanging hanging weight.
- When the ground shakes due to an earthquake the base of the seismograph shakes too but the weight hanging doesn’t.
- Now, scientists measure the difference between the shaking part and the motionless part.
- The seismogram shows wiggly lines, if the lines are less wiggly then it means a small earthquake and if the lines are much wiggly then it is a large earthquake.
- According to scientists, the length of the wiggly line depends on the length of the fault and the size of the wiggle depends on the amount of sliding.
Who monitors earthquakes in India & how?
- National Center for Seismology (NCS) under the Ministry of Earth Sciences, Government of India is responsible for monitoring the earthquakes along with, National Disaster Management Authority (NDMA) which looks after the preparedness against earthquakes.
- The study of earthquakes in India happens through seismic zone mapping given by the Bureau of Indian Standards (BIS).
- According to the seismic zone maps, India has four seismic zones.
- The most active seismic zone is zone V and the least is zone II.
- According to the head of the concerned ministry, 11% of the country falls in seismic zone V, 18% in zone IV, 30% in zone III and the remaining in zone II.
With this, the crackdown on earthquakes comes to an end. We hope we could touch upon all the aspects related to an earthquake and could cater to some of your queries. For more informative content, stay tuned.