Causes, Effects and Geographical Distribution of Earthquakes
Causes of Earthquakes
Earthquakes are caused by disturbances in the interior of the earth and other causes.
- Tectonic Movements: The disturbances inside the earth are called tectonic movements. These forces bring about changes on the earth surface and physical features like mountains, plateaus and rift valleys are formed. Most disastrous earthquakes are caused by tectonic forces. Tectonic forces create tension and pressure and the stress begins to build up inside the earth. When the stress tends to be more than what the rocks of the earth can bear, the rocks are broken and displaced from their state of equilibrium. It is known as faulting. The energy accumulated during faulting is released. This release of energy gives rise to mighty waves. These waves originate from a point called Focus in the interior of the earth and then spread out in all directions. On the surface whatever comes into their contact begins to vibrate. The chief cause of earthquakes felt often in California in the USA is often the San Andreas Fault found there.
- Volcanic Eruptions: The volcanic eruptions are often very violent and cause vibrations in the earth crust. Sometimes the vent of a volcano is blocked temporarily and explosive eruption takes place suddenly causing tremors in the earth crust. The Krakatoa that erupted in 1883 became the cause of a violent earthquake there.
- Other Reasons: The roofs of underground caves sometimes give way and release great force to cause minor tremors in the earth crust. Nuclear explosions also release massive energy to cause tremors in the earth crust.
Effects of Earthquakes
Earthquakes are less advantageous and more harmful to man. Damage done is chiefly in following respects:
- Loss of Property: Severe earthquakes reduce to rubble human structures ranging from huts to palaces and single storey to multi storey buildings. Even pipelines laid under the ground and railway lines are damaged or displaced. The best example of this type of damage is Koyana earthquake in 1970.
- Loss of Life: Earthquake tremors of a few seconds takes the lives of thousands of people. Many people have been rendered homeless or suffered injuries in various ways.
- Changes in the course of rivers: On account of the impact of earthquakes, sometimes rivers also change their course. Consequently, when floods come they play havoc with people's lives.
- Tsunamis: The earthquakes in the sea generate massive waves called Tsunami in Japanese language. It sometimes rises to the height of 20-25 metres. It causes great damage to life and property of people living in coastal areas as well as to tourists. Tsunami caused by an earthquake in the sea near Sumatra on 26th Dec, 2004 hit southeast Asian countries including India and Sri Lanka. There was heavy damage in these countries. More than 3 lakh people died.
- Mud Fountains: On account of earthquakes of high intensity, warm water and mud fountains also burst.
- Cracks in Earth Crust: Earthquake cause cracks in earth's crust anywhere in fields, roads, parks and even hills. They are thus rendered useless. The San Andreas fault in California, U.S.A. was created in a similar manner.
Did You Know?
About 90% of the world's earthquakes and 81% of the world's largest earthquakes occur along the Ring of Fire.
Geographical Distribution of Earthquakes
It is true that the earthquakes can happen in any part of the world. But in the areas of faulting and folding or of crustal weakness, the frequency of earthquakes is more than anywhere else. The earthquakes are concentrated in two main belts.
- Circum-Pacific Earthquake Belt: This belt includes all the coastal areas around the vast pacific ocean. This belt extends as an isostatically sensitive zone through the coasts of Alaska, Aleutian Islands, Japan, Philippines, New Zealand, North and South America. This zone accounts for 68% of all earthquakes on the surface of the earth. The most talked about earthquake areas in this zone include Japan, Chile, California and Mexico.
- Mediterranean-Asia Earthquake Belt: This belt begins from Alps mountain range and passes through Turkey, Caucasus Range, Iran, Iraq, Himalayan mountains and Tibet to China. One of its branches passes through Mongolia and Lake Baikal and another branch extends to Myanmar. About 31% of world's earthquakes are located in this region.
- Other Areas: These include Northern Africa and Rift Valley areas of the Red Sea and the Dead Sea. In addition to these, the ocean ridges are also active earthquake zones.