Causes of Earthquake

Earthquake:

        Earthquake is the sudden and rapid shaking or rolling of the Earth’s surface caused by the release of stress stored in rocks. It is an incidence of tremors / lateral movement or ground displacement caused by pressure dynamics within and below the earth's crust or due to volcanic activity. It is the tremors which are produced by the passage of vibratory waves through the rocks of the earth. The vibration or shaking of the earth’s crust proceeds in the form of waves from the centre of the disturbance.

        

         The surface where they slip is called the fault or fault plane. The location below the earth’s surface where the earthquake starts is called the hypocenter, and the location directly above it on the surface of the earth is called the epicenter.

Taking the earth as a whole earthquakes of one kind or another take place almost every minute, but the great majority of them are so feeble that their occurrence is not felt by man except through highly sensitive instruments.

       

        Sometimes an earthquake has foreshocks. These are smaller earthquakes that happen in the same place as the larger earthquake that follows. Scientists can’t tell that an earthquake is a foreshock until the larger earthquake happens. The largest, main earthquake is called the main shock. Main shocks always have aftershocks that follow. These are smaller earthquakes that occur afterwards in the same place as the main shock. Depending on the size of the main shock, aftershocks can continue for weeks, months, and even years after the main shock!

      Aristotle was the first man who for the first time related the phenomena of earthquake to physical factors. In a very general sense all earthquakes have the same cause. They are caused by the release of stress in the earth's crust. the higher the stress the more potential for movement.

       There are four different types of earthquakes: Tectonic, volcanic, collapse and explosion.

1.Tectonic Earthquakes:

       A tectonic earthquake is one that occurs when the earth's crust breaks due to geological forces on rocks and adjoining plates that cause physical and chemical changes. The earth’s crust is composed of loose, cracked fragments of lands referred to as tectonic plates. The plates are floating on the mantle and are moving slowly and gradually. The movement of these plates occurs in different forms; towards each other, away from each other, sliding past each other or colliding with each other. When 2 moving tectonic plates slide over one another then a huge tremor is occurs. This type of earthquake is known as tectonic earthquake. This type of earthquake is the most prevalent kinds of earthquakes in the world. Its magnitude may be small or large. Tectonic earthquakes have caused most of the planet’s mass destruction. Tremors triggered by tectonic earthquakes are always severe, and if their magnitude is high, they are capable of bringing down an entire city in seconds.

        The earthquake which took place near the cost of Portugal due to tectonic cause

2.Volcanic Earthquakes:

A volcanic earthquake is any earthquake that results from tectonic forces which occur in conjunction with volcanic activity. Compared to tectonic earthquakes, volcanic earthquakes are less prevalent. This type of earthquake is typically take place before or after an eruption. Volcanic earthquakes come in two forms-

 Long-period volcanic earthquakes.

 Volcano-tectonic earthquakes.

Volcano-tectonic earthquakes usually happen after a volcanic eruption. During an earthquake, magma erupts from inside the earth’s crust leaving a space behind. The space left after magma eruption must be filled. To fill it, rocks move towards the space resulting in severe earthquakes. It is noticed that, numerous occasions, magma blocks the vents during a volcanic activity. This means that the high pressure fails to be released. The buildup of pressure becomes unbearable and releases itself with a massive explosion. The massive explosion results in a ruthless earthquake.

3.Explosion Earthquakes:

An explosion earthquake is an earthquake that is the result of the detonation of a nuclear and/or chemical device. These are caused by nuclear explosions. They are, essentially, man triggered kind of earthquakes and represent the biggest impact of modern day nuclear war. During the 1930s nuclear tests conducted by the United Sates, numerous small towns and villages were devastated as a result of this grave act.

4.Collapse Earthquakes:

A collapse earthquake is small earthquakes in underground caverns and mines that are caused by seismic waves produced from the explosion of rock on the surface. They are sometimes referred to as mine bursts. Collapse earthquakes are instigated by the pressure generated within the rocks. This kind of earthquake leads to the collapse of the roof of the mine instigating more tremors. Collapse earthquakes are prevalent in small towns where underground mines are located.

The Tectonic and volcanic earthquakes are natural earthquakes, which we cannot stop and the explosive and collapse earthquakes are the manmade earthquakes, which can be stopped.