An earthquake occurs when earth releases energy suddenly in the form seismic waves. The tectonic plates in the earth’s crust which are almost hundred kilometers in thickness get dislocated because of seismic waves. An earthquake is a natural phenomenon. But sometimes activities like oil drilling, coal mining, and construction of big dams also add up to the seismic activity. Earthquake intensity is measured with the help of seismometers. It is also known as Richter scale. A magnitude of 3 on Richter scale is indiscernible whereas a magnitude higher than 7 usually causes damage and destruction. One of the worst earthquakes to hit was a magnitude of over 9 in Japan in 2011.
The damage caused due to an earthquake depends on the location of the epicenter of the earthquake. Major destruction occurs near the epicenter of the earthquake because maximum intensity locates at the center. Sometimes because of earthquakes there may be volcanic eruptions and landslides.
Naturally occurring earthquakes
Earth’s tectonic plates are marked by faults or fractures. When the tectonic plates slide past each other or have a collision with each other, an earth quake occurs.
Size and frequency
Almost 500,000 earthquakes occur each year that can be detected with the latest instruments. Among these, around 100,000 can be felt. Minor earthquake prone areas on earth are Italy, Greece, New Zealand, Turkey, Portugal, Pakistan, Iran, Indonesia, Peru, Chile, Guatemala, Mexico, California and Alaska. Majority of earthquakes occur in the course of 40,000 km long circum-Pacific seismic belt which is in the shape of a horseshoe. Himalayan mountain plate is another zone where massive earthquakes may occur. With rapid rise in population in countries like Japan, Mexico and Tehran, because of their presence in seismic zones, major earthquakes may occur. If we list out the top 10 earthquake prone countries, it goes like:
3. United States of America
4. New Zealand
8. Papua New Guinea
10. Solomon Islands
Human induced seismic activity
As there is a lot of development and enhancement in technology, man has exploited the wealth of the nature. The important activities that lead to earthquakes are drilling for oil wells, coal mining, and collecting large volumes of water for construction of a dam. As an example, the 2008 Sichuan earthquake that occurred in China was because of the construction of a dam. In Australia also there was coal mining activity which resulted in an earthquake.
Impact of earthquakes
A number of natural changes occur due to an earthquake.
The ground shakes and ruptures because of which building and other structures get damaged. The severity of destruction depends on how close the area is to the epicenter. Ground rupture means the breakage and displacement of the earth’s surface. It is a major threat to huge structures like bridges, dams and nuclear powerplants.
Another major threat that occurs due to an earthquake are landslides. When the earthquake is accompanied by other major threats like wildfires, volcanic activity or storms, landslides may occur.
Due to the damage of electrical power or gas lines chances of fire eruption are high due to an earthquake.
When water saturated granular material like sand loses its strength due to earthquake it gets modified into a liquid. This process may cause damage to bridges and buildings. There is a chance of these structures getting collapsed to the ground.
When earthquake occurs in the sea bed, the sea waves rise in the sea with long and sudden movements dispensing large volumes of water. Depending on the depth of the water these waves travel at a speed of 600-800 kilometers per hour. These waters are capable enough to drown the structures and building all along the sea coast. Usually tsunamis occur in the seal when the earthquake hit is above 7.5 on the Richter scale. After the tsunami in 2003 that devastated lakhs of people across Indian Ocean, countries all over the world are taking precautions and have invested in tsunami warning systems.
A major earthquake causes lot of destruction and damage to buildings and structures. Because of lack of basic amenities, diseases may spread. It will take lot of time for rehabilitation of people.
Man has been making a steady progress in all fields. There are several discoveries and innovations to his credit. Except for being ready to face any type of natural calamities, there is nothing that man can do in such circumstances. Time and again nature proves that it is mightier than human beings.