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Views: 205 Description: Recent earthquake in Afghanistan of 7.5 magnitudes was a huge one. This comes a few months after another one in Nepal which devastated the pristine Himalayan country causing enormous loss of life and property. Scientists are working tirelessly to figure out how to predict them, as any advance warning even of a few minutes can save a lot of lives. But the success has eluded them. However years of research have given them lots of insight into the science of earthquakes. In this series we will try to go deeper into this science.
The first thing that comes to my mind is why do these happen? Are they an act of God?
For this we will have to look at brief history of earth creation.
Long time back lots of material fused together to form the earth This fusion generated a lot of heat and slowly as the earth cooled down denser material sank towards the center and lighter material rose to the top.
So we can divide the earth in 4 parts, very thin crust, mantle, hard inner core and outer core. The inner core is solid however the mantle is liquid and can flow.
Due to this large difference temperature and pressure, convection currents develop in the mantle and the mantle material flows( this sounds better- whose material flows from inside to outside) similar to convection currents that we can see while heating water.
The moving mantle causes the crust sitting on top of core to move or slide.
Earth crust slides in big pieces and these huge pieces of crust that slide are called Tectonic plates. There are 7 of them. These plates constitute the whole of earth's crust but they slide in different directions at different speeds. On an average these plates move few centimeters a year.
It is this extremely slow differential movement of plates that causes earthquakes. Let's see how.
Consider a rubber band. You can keep stretching the rubber till it hits a limit and snaps. At that time all the energy stored in the rubber releases. When we have seen this when we try to hit our friends with slings.
Now earth tectonic plates are made of elastic and brittle rocky material which also keeps sliding (very very slowly) against each other. The line where these plates meet is called the fault. The plates keep sliding and storing energy till the plates cannot slide anymore and snap back.
This sudden slip at the fault releases the stored elastic energy and causes earthquake. And the energy released is enormous. 2001 Bhuj earthquake in India released energy equivalent to 400 times the Hiroshima nuclear bomb.
The released energy is spread by the seismic waves which travel along the earth surface. These waves cause the shake the ground violently and cause huge devastation far and wide.
Once the energy is released and earthquake is over the movement of plates and process of energy storing at the fault starts again almost like waiting to snap and cause the next one.
Most of the earthquakes happen at fault line or places where plates meet. However some earthquakes also happen away from fault like the 1993 Latur earthquake in India. At these places the plates break causing rise to new fault lines.
So we saw that this devastating natural process is earths due to convective currents in molten earth which causes earth’s crust to slide and snap almost like a rubber band.
In the next video we shall dig deeper into seismic waves to see how the ground shakes during the earthquake.
This work is supported by IUCAA (www.iucaa.in) and TATA Trust (www.tata.com/aboutus/sub_index/Tata-trusts)
Credits:,Ashok Rupner, Manish Jain, Pradnya Pujari, Shivaji Mane, Jyoti Hiremath, Arvind Gupta, Vidula Mhaiskar TATA Trust: Education is one of the key focus areas for Tata Trusts, aiming towards enabling access of quality education to the underprivileged population in India. To facilitate quality in teaching and learning of Science education through workshops, capacity building and resource creation, Tata Trusts have been supporting Muktangan Vigyan Shodhika (MVS), IUCAA's Children’s Science Centre, since inception. To know more about other initiatives of Tata Trusts, please visit www.tatatrusts.org....