 earthquakes. They are one of the dangerous events in the environment. See whenever we see earthquakes in the news, what do we see? We see an entire building collapse to the ground, people roaming in the streets in panic, people losing their lives or people hiding under the table, right? But have you ever wondered what causes this massive event or where it gains the strength to collapse an entire building? All the answers to your questions lies in this video. Watch it fully. See in simple words an earthquake is the shaking of the earth. See it is a natural event and caused due to the release of energy which generates waves that travel in all directions. Now you may have a doubt. From where this energy is released and why does the earth shake? See the release of energy occurs along a fault. Here a fault is a sharp break in the crustal rocks. Know that the rocks along the fault tend to move in the opposite directions. But however their tendency to move apart at some point of time overcomes the friction. And as a result of friction these blocks get deformed and eventually they slide past one another abruptly. That is quickly. And this causes a release of energy and the energy waves travel in all directions. See this abrupt or quick slide past event causes the shaking of the earth. Know that the point where the energy is released is called the focus of an earthquake. And it is also called the hypo center. See the energy waves traveling in different directions reach the surface. The point on the surface that is nearest to the focus is called the epicenter. See the epicenter is the first one to experience the energy waves and it is a point directly above the focus. Now talking about the types. See earthquake waves are basically two types. They are body waves and surface waves. Firstly let's see about body waves. See body waves are generated due to the release of energy at the focus and they tend to move in all directions. Know that body waves travel throughout the body of the earth. And then the body waves interact with the surface rocks and they generate new set of waves called the surface waves. Now let's see about the surface waves. See surface waves move along the surface of the earth. Here the velocity of the waves changes as they travel through materials with different densities. So denser the material the higher is the velocity. And also note that the surface waves are the one that are most destructive. They cause displacement of rocks and collapse of structures like buildings houses etc. So this is about the surface waves. See as for us the types of earthquake waves we saw two types. One is body waves and the other one is surface waves. And the body waves it is further classified into two types. One is P waves that is the primary waves and the other one is S waves that is the secondary waves. Firstly let's see about the P waves. See they move faster and they are the first to arrive at the surface and that is exactly why they are called as primary waves. See these P waves they are similar to sound waves. So they travel through gaseous, liquid and solid materials. Now the second type is S waves. See they arrive at the surface with some time lag and these are called as secondary waves. An important fact about S waves is that they can travel only through the solid materials. And this only helped the scientists to understand the structure of interior of the earth. So this is all about the basics of earthquakes and the types of waves. Now finally let's see how earthquakes are measured. See earthquake events are measured using two scales. They are magnitude scale and intensity scale. See the magnitude scale is known as the Richter scale. Here the magnitude relates to the energy released during the earthquake. In Richter scale the magnitude is expressed in absolute numbers that is from 0 to 10 and this is about the magnitude scale. The second one is intensity scale and it is also known as Merkali scale. Here the intensity scale takes into account the visible damage caused by the earthquake event and the range of the intensity scale is from 1 to 12. I hope you all got an idea about what is earthquake, how it is happening, why it is damaging the infrastructure on the surface and how it is measured. So if you want to know more geographic events like this subscribe to Shankar Iyer's Academy's YouTube channel. And if you are an UPSC aspirant and if you want to know more about geography related topics watch daily Hindu news analysis of Shankar Iyer's Academy.