Why Earthquake Happens?
The reason for the earthquake in India and Nepal is understood well. The northern parts of India and Nepal are more prone to earthquakes because two of the tectonic plates have a strong joint. One is the Indian plate, and other is the Eurasian plate. It can be understood like this; when the forehead of the human body is hit on the hard surface, the hard lump is visible. This is caused due to the blow or impact rupturing underlying blood vessels. In the same way, the lumps or Himalayan mountains were formed when Indian plate moved with high pressure and got collided with Eurasian Plate. It probably caused great earthquakes at the time but still the plate moving with 2-4 cm/year. This causes the increase in the height of the mountain range. As an example, the height of Mount Everest is increasing by the rate of around 4mm/year.
Motion of tectonics and earthquake waves.
The motion of the plates results in the rocks to collide under the surface of the earth. When the two rocks hit the surface, it makes us feel the vibration. The other reason is the passage of convection from the magma to the surface of the earth. These conditions create different types of waves which acts as vibrations. The waves are named as P wave or Primary wave; they are longitudinal waves coming first to the seismograph, the S wave or secondary wave, they move transverse to the surface after the P wave have its impact, the last being the surface wave which is the mechanical waves slower than P and S waves. The mechanical waves can be felt more on large earthquakes.
How to detect and Predict?
These waves can be recorded on the device called as the seismograph, but the condition is as simple. “Just like police says, I will investigate only after crime scene, Seismograph says to the earth, create an earthquake after that only I will detect it” This metaphoric statement is similar in such a way that police come for investigation just after the crime scene. The impact of collision or convection here is like a crime scene, and investigation of police is recording in seismograph.
On the above metaphor let crime scene be the breaking of the bones causing death. On investigation, the first work of the expert is apparent to observe the bones by X-ray. With these rays, the fractures or fault and the damage to the bone can be easily identified. The non-damaged bones are also visible. With X-ray, the bones can be seen due to the ability of bones to absorb it due to their material property, but in case of looking in through the earth surface, it is not possible because of the different material properties of internal rocks. Now for satisfaction, just above X-Rays we have gamma rays but it may not be possible. Another argument is that; just before earthquake there is Emission of Radon gas or even Methane but still it cannot be predicted..