- There are two main types of earthquakes: natural and man-made.
- There are many different subtypes of earthquakes: tectonic, volcanic, collapse and explosion. Naturally occurring (tectonic) earthquakes occur along tectonic plate lines (fault lines) while man-made earthquakes are always related to explosions exploded by man.
- Types of earthquakes are as follows:
- Tectonic earthquake
- Volcanic earthquake
- Collapso earthquake
- Explosion earthquake
- Reservoir induced earthquake
1. Tectonic earthquake:
- The earth’s crust consists of loose broken fragments of lands known as the tectonic plates.
- These tectonic plates have the ability to slowly and gradually move.
- Now, these plates can move away from each other, towards each other, can collide or can slide past each other.
- When the two tectonic plates slide over each other a huge tremor takes place, and that’s how a tectonic earthquake occurs.
- Tectonic earthquake are the most common type of earthquake. It may be of small or of extremely high magnitude.
- Most of the mass destruction caused by an earthquake over the history is due to the tectonic earthquake.
- The tremors caused by tectonic earthquake0 are mostly severe and if they are of high magnitude, they can completely destroy a whole city within seconds.
2. Volcanic earthquake:
- Volcanic earthquake are comparatively less common. than the tectonic earthquake and usually occur either before or after a volcanic eruption.
- There are two types of volcanic earthquakes: Volcano tectonic earthquake and Long period volcanic earthquakes.
- The volcanic tectonic earthquake occur usually after a volcanic activity has taken place.
- The magma that erupts during an earthquake leaves a space, to fill the space left by the magma the rocks move towards the space to fill it in, causing severe earthquakes.
- Most of the times after the release of lava, the lava falls on its vent blocking it, and not letting the pressure release.
- The retained pressure does not stay for long; it releases with a huge explosion.
- The explosion causes a severe earthquake, mostly of extremely high magnitude.
3. Collapse earthquake:
- Collapse earthquakes are small earthquakes occurring in regions of underground caverns and mines.
- The immediate cause of ground shaking is the collapse of the roof of the mine or cavern.
- An often- observed variation of this phenomenon is the so called “mine burst”.
- This happens when the induced stress around the mine working because large masses of rock to fly off the mine face explosively, producing seismic waves.
- Collapse earthquakes are also produced by massive land-sliding.
4. Explosion earthquakes:
- The explosion earthquakes are caused due to the nuclear explosions.
- These man induced earthquakes are one of the biggest side effects of the modern nuclear war.
- In the 1930s during the American nuclear tests many small villages and towns suffered through such tremors,many of them were completely destroyed due to this heinous act.
- When a nuclear device is detonated in a borehole underground, enormous nuclear energy is released.
- In millionths of a second, the pressure jumps thousands of times the pressure of the Earth’s atmosphere and the temperature increases by millions of degrees.
- The surrounding rock is vaporised, creating a spherical cavity many metres in diameter.
- Some underground nuclear explosions have been large enough to send seismic waves throughout the Earth’s interior, waves with amplitudes equivalent to moderate sized earthquakes that have been recorded at distant seismographic stations.
- Some explosions have produced waves that have shaken buildings in distant locations.
5. Reservoir induced earthquakes:
- These earthquakes have been subject of study and some controversy.
- Local seismicity increased significantly after the construction of Koyna dam.
- While the effect of weight of the impounded water is likely to be negligible at the depths of the induced seismic activity, an increase in pore water pressure that migrates as a pulse away from the reservoir after filling may have been sufficient to reduce the strength of the rock to the point where rupture could occur.