One of the most horrible natural disasters is earthquake which has not only ability of eradicating even entire cities but also they can be a cause of tsunamis and devastation on huge scale.
So far human science has only been able to predict the fault line (danger zone) but still it is unable to guess the exact time and magnitude of the quakes. The main cause of earth quakes is the tectonic plate movements. The upper layer of earth is divided into many parts called tectonic plates; these plates are continuous movement and cause faults. There are three types of movements of plates. Firstly when these plates move away from each other they form normal faults and create ridges and rift valleys in ocean. Secondly plates move towards each other which create a reverse or thrust fault these plates either collide to form mountains or slide below the other. Thirdly there is the transform plate boundary of plates in which the two parallel plates sliding past each other to create a strike-slip fault.
The knowledge of fault line can only alert about the danger areas. Thus the people adapt their lifestyle specially their infrastructure according to the risk. Though secondary effects of an earthquake, for example, avalanches and fire flame from burst gas lines can be deadly, the fundamental driver of death and pulverization amid quakes is generally the collapse of buildings. Thus, in many rich countries structures near the fault lines are made to withstand the violent shock waves, but unfortunately when a quake hit the poorer country devastation is usually at a larger scale
How earthquake is caused:
Earthquake is caused by the build up of pressure that is made when tectonic plates collide. In the end the plates slip past each other and an immense measure of energy is discharged, sending seismic waves through the ground. The time when the break happens is frequently a few kilometres underground and is known as the focus or hypocentre. The point straightforwardly above it is the epicenter, and this is the place where greater part of the harm is caused. Earthquakes have diverse characteristics depending on their type of fault line, but when they occur underwater, they can sometimes trigger enormous destructive waves called tsunamis.
How Earthquake occur:
Friction causes pressure:
As the tectonic plates are pushed past or into each other, friction keeps them from moving and causes a generation of enormous pressure.
Energy is discharged:
At the point when the pressure overcomes the friction, the plates all of a sudden crack and slip past each other, discharging energy and causing seismic waves.
The process starts again:
Once the energy has been discharged, the plates will expect their new position and the process will start once more.
Types of Seismic Waves:
P (Primary) waves go forward and backward through the Earth crust, moving the ground in accordance with the direction of wave. Primary waves the fastest moving seismic wave going at around 6-11km/s (3.7-6.8mi/s), thus regularly arrive first with a sudden crash.
S (Secondary) waves travel up and down, perpendicular to the direction of the wave, causing a rolling motion in the Earth crust. They are slower than Primary waves, going at around 3.4-7.2km/s (2.1-4.5mi/s), and can just travel through strong material, not liquid.
Unlike P and S waves, surface waves just move along the surface of the Earth and are much slower. Love waves, named after the British seismologist AEH Love, are the quicker of the two types and shake the ground side to side perpendicular to direction of the wave.
Earthquakes are measured utilizing an instrument called a seismograph, which creates a visual record of tremors in the Earth crust. The smaller however, quicker P waves appear first, trailed by the bigger yet slower S waves and surface waves. The measure of time between the entry of the P and S waves indicates how far away the quake was, enabling researchers to work out the correct area of the epicenter. The size of the waves allows scientist to determine the magnitude or size of the earthquake, by using the instrument called Richter scale.
As of now, earthquakes can’t be anticipated sufficiently far ahead of time to give people much notice, yet there are some early warning frameworks set up to give people few seconds or minutes to get ready before the earthquake hit. At the point when seismometers recognize the underlying P waves, which more often than does not cause much harm, they can gauge the epicenter and greatness of the quake and alarm the neighborhood populace before the more dangerous S waves arrive.