An earthquake is a phenomenon where the land vibrates or moves back and forth. This movement is caused by waves of flexible compression passing through the earth’s crust. Essentially, an earthquake is a disturbance of the earth’s crust that causes the land to move in a back-and-forth motion.
When an event occurs inside the earth, causing a sudden trembling of a part of the earth’s surface, it is known as an earthquake. According to Barchester, “Earthquake is the vibration of the surface which arises in the short-term disturbance of the elastic or gravity equilibrium of the surface or the rocks below it.”
Earthquake waves spread outwards from a center, and their power gradually decreases in all directions. The earthquake consists of several movements, which come to an end gradually. During an earthquake, trees, upper parts of temples, and tall objects are known to move back and forth. In addition to undulating motions, earthquakes can also cause surface subsidence. Thunder-like sounds are also heard from the land and atmosphere during an earthquake.
Major Effects of Earthquake
- Volcanoes: When a volcano erupts, the areas near its mouth can tremble and shake, causing an earthquake. Even in the absence of an eruption, earthquakes can occur in regions near volcanoes due to the force of material trying to escape the earth’s crust and being obstructed by hard rocks above.
- Earth’s Collapse: Many scholars believe that as the earth’s temperature gradually decreases, it causes the earth to shrink, resulting in chaos in its layers and vibrations in various parts of it, which can cause earthquakes.
- Isostasy Theory: According to scientists, isostasy refers to the balance of the earth’s surface rocks that are sinking into geological rocks. As the higher ground erodes and deposits into lower parts, the higher ground rises to maintain equilibrium, and the lower ground gets pushed down. As a result, there is a rise in the area of decreased load and a depression in the area of increased load, which helps to maintain balance.
- Fault Actions: When there is pressure from opposite directions in the upper crust of the earth’s surface, it can bend and crack, causing rocks in the crust to move up or down depending on the extent of the crack. This action generates vibrations in the nearby area, and even after the major shock of the earthquake, short-term shocks continue for some time because the rocks keep moving for a while after breaking.
- The Best Gases of the Earth: When the water reaches the earth’s crust, it reaches hot rocks and immediately turns into steam, which tries to escape. When this action happens quickly, the surface can start shaking and cause a powerful earthquake.
- Artificial Earthquakes: Human actions can cause earthquakes, such as actions that put a lot of pressure on the surface. For example, the detonation of an atomic bomb in Hiroshima, Japan, caused an earthquake. The movement of trains and the shifting of snow and rock blocks can also cause vibrations on the surface and lead to earthquakes.
Type of Earthquake
There are many types of earthquakes, which are classified on different grounds. They are described below
There are many types of earthquakes classified on different grounds, which are described below:
- Based on the cause of origin: Earthquakes can be categorized into two categories based on the cause of origin:
(a) Artificial earthquakes: These include earthquakes whose origin is due to human actions. An earthquake caused by human activities is called an artificial earthquake, such as from a bomb blast or other disturbances caused by humans.
(b) Natural earthquakes: If the disturbance causing the earthquake is due to natural causes, then it is called a natural earthquake. These can be further divided into two parts:
(i) Volcanic earthquakes: These earthquakes occur due to the eruption of the volcano or the intrusive actions of the volcano. Similar earthquakes occur in Japan.
(ii) Tectonic earthquakes: These earthquakes occur due to the movements on the earth’s surface. Earthquakes occurring in India or other mountainous regions are of this type.
- Based on the nature of the origin of movements: Earthquakes are also classified based on the nature of the origin of the movements. There are two classes of earthquakes based on this:
(a) Tectonic earthquakes: These occur due to sudden pushes from the ocean or continuous pushes that generate many wave motions or vibrations one after the other on the adjacent rocks. Geological movements such as ring and rift bursting cause movement in the earth’s surface, leading to tectonic earthquakes.
(b) Volcanic earthquakes: In a volcanic eruption, the geothermal fluid finds a way out. Naturally, there are shocks to the crust immediately before, during, and after the eruption, leading to vibrations on the earth’s surface. These shocks can be very intense and harmful. But it should be remembered that not all volcanic eruptions are earthquake-producing.
Earthquake Belts
Earthquake belts are regions where earthquakes frequently occur, and they are typically found in areas of fold mountains and near the shores of the sea. There are two main earthquake belts:
- The circum-Pacific belt, also known as the Pacific Ring of Fire, surrounds the Pacific Ocean from the southern tip of the Andes to Alaska and from Kamchatka to New Zealand.
- The Middle Atlantic Ocean and Mediterranean Belt, which runs from the Pyrenees to the Himalayas.
Famous scientist Mantissa de Valor discovered that earthquakes occur more frequently in the outer direction of mountains and where the slope is higher. However, volcanoes are also found in the inner seaside of mountains. Earthquakes are related to the standing temporary edges of newly folded mountains. The Bihar earthquake is an exception as it occurred in areas of low slopes.
About 40 percent of earthquakes occur in the first belt, and 54 percent occur in the second belt. Severe earthquakes occur in the circum-Pacific belt due to the combined action of stratification and volcanic eruption.
In the Middle Atlantic Ocean and Mediterranean Belt, many parts are thousands of kilometers away from volcanoes, and one branch of this belt is spread over the mid-oceanic coast. Its most active part is at the equator. The second branch of the belt extends through the Jordan Valley to the rift valley of East Africa, and one of its branches goes to the Indian Ocean via the Aravana peninsula.
Effects of Earthquake
Earthquakes are a natural phenomenon that can have both destructive and constructive effects on the Earth. Unfortunately, the destructive effects on human beings are considered a curse. Here are some of the destructive effects:
- Damage to man-made structures
- Destruction of cities
- Outbreak of floods
- Landslides
- Cracks in different parts of the Earth’s surface
- Uplift and subsidence of land
- Origin of fires or fires caused by broken gas lines or electrical wires
- Generation of water waves, which can cause further destruction
However, earthquakes can also have beneficial effects on the Earth, such as:
- Earthquake-induced landslides can help in weathering and bring fertile soil to previously infertile areas, making them cultivable.
- Sudden folds of rocks and faulting can create new water sources that are beneficial to humans.
- Earthquakes can create new landforms, such as deep oceans or sudden rises in the land, which can be beneficial to humans as natural landscapes.
- Large cracks in the surface can mix minerals, making them more accessible for mining.
- When the terrain becomes particularly bumpy due to an earthquake, scientists can better understand the internal structure of the earth’s crust.