An Earthquake is shaking of surface of Earth resulting from sudden release of energy in the earth's Lithosphere that creates seismic waves. Earthquakes on the Earth can occur naturally or by the human beings.
Earthquake occurring naturally
1. Interplate
Occur due to movement of two tectonic plate due to convergence movement, Divergent movement and Transform movement. Due to convergence movement, all three types of earthquake can occur which are shallow focus, medium focus and Deep focus earthquake. Due to Divergent movement mostly shallow focus type of earthquake occur and very rarely medium focus occur. Due to Transform movement also mostly shallow focus occur and very rarely medium focus occur.
- Shallow focused Earthquake: This originates from the shallowest point of interaction between the two plates.
- Medium focus Earthquake: Point of interaction is below shallow focus point.
- Deep focus Earthquake: Originates from the point deep below at the subducting plate. When the subducting plate reaches the magma, it breaks there and causes an earthquake.
2. Intraplate
These earthquake occur within the interior of tectonic plate. It occur because of minor fault lines. Due to compression of tension, energy might be released causing a earthquake. It the earthquake in the region that makes us realize the existence of such fault lines, which might earlier were un-noticed.
Shallow focus Earthquake are more destructive as they are closer to earth's surface. Deep focus earthquake needs to emit a substantial amount of energy to be destructive because some energy get dissipated while traveling towards surface.
Ways to measure Earthquake
Measured on basis of Intensity and Magnitude. Older scale on basis of Intensity is Mercalli scale. Scale of intensity ranges from 1 to 12, where 1 is not felt and 12 is complete destruction. On the basis of magnitude older scale is Richter scale. This scale ranges from 0 to 8. Every 1 unit is 10 times more shakier from previous unit. Richter scale cannot measure earthquake greater than 8 units, for measuring earthquake of magnitude more than 8, Moment earthquake scale is used. Moment earthquake scale is used in the same way as the Richter scale is used,but for magnitude more than 8 units. The moment earthquake scale gives a more accurate reading than Richter scale.
Man-Induced Earthquake
1. Reservoir induced Seismicity:
Dams creating reservoirs store huge amount of water which over a period put ample pressure on the ground which can lead to earthquake. Ex. Three gorges Dam, in China.
2.Waste water Injection:
Industries many time injects waste water back into the ground, depending on how much water it pumped into the ground, pressure which builds up leads to an earthquake.
3.Mining related Earthquake:
Fossil fuels extraction causes instability leading to sudden collapses which may trigger earthquake.
4.Geo-Thermal Energy based:
Traditional geothermal drilling bores into hot rock such as sandstone that has water or steam trapped in its pore spaces and natural fractures. The drilling itself does not cause earthquakes, but the steam removal and water return can do so, by producing new instability along fault or fracture lines.
Earthquake prone region
- Circum-pacific belt
- Himalayan region
- Mid Atlantic Ridge
- African Rift Valley Region
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