Geography Notes: Causes of Earthquake
Geography Notes on Earthquake for SSC CGL 2018. These notes will also be useful for other competitive exams like banking PO, SSC CGL, MTS, CPO, CHSL, Railway etc.
▣ The study of seismic activity gives valuable information about the interior structure of the Earth.
▣ Earthquake is a natural event and involves shaking of the ground.
▣ A thorough study and observations of this phenomenon has helped in understanding of innermost parts where this occurs.
▣ An Earthquake is the shaking or vibration/tremors in the Crust, caused as a result of internal forces and volcanism in the Earth.
Types of Earthquakes
- Tectonic earthquakes: These are produced due to sliding of rocks along a fault plane.
- Volcanic earthquake: These are confined to areas of active volcanoes.
- Collapse earthquake: The roofs of underground mines collapse causing minor tremors in the areas of intense mining activity.
- Explosion earthquakes: These occur due to the explosion of chemical or nuclear devices.
- Reservoir induced earthquakes: These occur in the areas of large reservoirs.
Measurement of Earthquakes
All earthquakes are different in their intensity and magnitude. The instrument for measurement of the vibrations is known as Seismograph.
- Magnitude scale: Richter scale. Energy released during a quake is expressed in absolute numbers of 0-10.
- Intensity scale: Mercalli scale. It measures the visible damage caused due o the quake. It is expressed in the range of 1-12.
1. Volcanic Eruptions
- Such type of earthquakes occurs in areas, with frequent volcanic activities.
- When boiling lava tries to break through the surface of the earth, with the increased pressure of gases, certain movements are caused in earth’s crust.
- Movement of lava beneath the surface of the earth can also cause certain disruptions.
- This sends shockwaves through the earth, causing damage.
- These earthquakes are mild.
- Their range is also limited.
2. Tectonic Movements
- The surface of the earth consists of some plates, comprising of the upper mantle.
- These plates are always moving, thus effecting earth’s crust.
- When two Constructive plates move away from each other, they correspond to mild earthquakes.
- Earthquakes of this type have varying intensities.
3. Geological Faults
- A geological fault is known as the displacement of plates of their original plane.
- The plane can be horizontal or vertical.
- These planes are not formed suddenly but slowly develop over a long period.
- The movement of rocks along these planes brings about tectonic earthquakes.
- These faults occur due to the impact of geological forces.
- The displacement of plates creates the fracturing of rocks, which releases a lot of energy.
- This type of earthquake can be disastrous.
4. Man Made
- The interference of man with nature can also become a cause of the earthquake.
- The disturbance of crustal balance due to heavy clubbing of water in dams can cause earthquakes.
- Nuclear bombing can send specific type of shockwaves throughout the surface of the earth, which can disturb the natural alignment of tectonic plates.
- Mining can also cause disturbance due to the extensive removal of rocks from different areas.
5. Minor Causes
- Some minor causes such as landslides, avalanches, the collapse of heavy rocks, etc. can also cause minor shockwaves.
- The gases beneath the surface of earth contract and expand, giving rise to movements in plates beneath the crust.
- The plutonic earthquake occurs because of adjustments in rock beds in the interior of earth’s crust.
- All these factors, correspond to minor earthquakes but sometimes these can also vary to moderate earthquakes.