Monday, February 06, 2017

Cause of Earthquake

Cause of Earthquake

1.Natural disturbances

2. Artificial disturbances

 1. Natural disturbance which  cause earthquake are:

 a) Volcanic cause
                            Volcanic earthquake is one that occurs in conjunction with volcanic activity. Volcanic cause sudden out burst or explosion. It produce vibration in nearby area. Volcanic eruption don't produce earthquake. Eruptions and earthquakes both result from tectonic forces in the rocks, they need not occur together.

b) Tectonic cause
                              It occur inside earth. According to theory, crust (outer layer) is made of rock & divide into many plates. plate are in motion in different direction and with different speed. These rock or plate have strain energy store in them. Sudden slip at fault result in release of strain energy in form of seismic wave which cause shaking of earth.
                              Earthquake which occur due to sudden release of strain energy as a result of sudden slip of fault is called Tectonic earthquake. Magnitude of earthquake depend on amount of energy release. 90% of earthquake is due to tectonic reason.

c) Landslide
                               Earthquake are also sometime produce by massive landsliding. For example landslide on April 25, 1974 along Mantaro river, Peru, produced seismic waves equivalent to a small to moderate earthquake. Part of the gravitational energy lost in the rapid downward movement of the soil and rock was converted to seismic waves.

d) Impact earthquake:
                              Meteorite strikes are such powerful that results in seismic waves. Example massive 1908 meteorite impact in Siberia.

2.Artificial disturbances

  a) Collapse earthquake:
                                   They occur in regions of underground caverns and mines. The immediate cause of ground shaking is the collapse of the roof of the mine or cave. When the induced stress around the underground workings causes large masses of rock to fly off the mine face explosively, it produces seismic waves.

b) Explosion earthquake:
                                     Ground shaking produced by the detonation of chemicals or nuclear devices. When a nuclear device is detonated in a bore hole underground, enormous nuclear energy is released. The pressure jumps to thousands of times the pressure of the Earth's atmosphere and temperature locally increases by millions of degrees. The surrounding rock is vaporized, creating a spherical cavity many meters in diameter. The cavity grows outward as boiling rock vaporizes from its surface, and the rock around it is minutely fractured by the shock of the explosion.
                                   The compression of the rock in the fractured region produces seismic waves that travel outward in all the directions. When the first compressive seismic wave reaches the surface, and if the wave energy is sufficient, it will blast the soil and rock away, throwing fragments of rock into the air.