Earthquake is severe thrilling of earth surface due to the passage of waves. This vibration in earth causes severe destruction if the waves are severe and strong. Earthquakes may be man made as well as natural. Earthquakes bring many changes with in and on the crustal surface of earth. Land masses may uplift as well as sit down. Deep trenches and gorges are formed in the result of earthquakes. High cliffs and ridges are also formed as a result of earthquakes. Whether the earthquake is man-made or a natural disaster, its magnanimity is not controllable. There are basically Three types of waves in an earthquake. Some of them are Compressional waves (P-waves) which move faster than any other type of wave. While some are transverse waves which moves slower than P-waves. These waves cause an up and down motion in the surface of Earth. These are less destructive as compared to P-waves.
Today many preventive and precautionary measures are being taken in order the minimize the destruction of an earthquake but before that one must know how an earthquake is caused. The main causes of an earthquake are as under;
01. Seismic Waves:
This is one and foremost reason for an earthquake. There are several types of earthquake waves including primary waves (P-waves), secondary waves (S-waves) and Love waves (L-waves/ Q-waves). However, Surface waves consist of several major types and are known as long waves. When these waves travel through earth mass cause severe disturbance and shake and thrill in the hard crust of earth. This type of disturbance is actually the earthquake. Most of the earthquakes in world’s history are the result of Seismic Waves. These waves are created by a sudden release of a stressed mass. Clarifying this phenomenon through and experiment is : Take two puffs of foam. Put these two puff along each other in way that their walls are touching each other. Then move the two puffs in opposite directions. For few seconds the walls of the puff will keep sticky with each other with a strain. But when the strain reaches to its ultimate end, the foams will suddenly move in transform position. This movement will cause sever vibration in both the puffs of foam. The same principle is with the land masses and tectonic plates. The sudden release of the strained bodies creates intense vibration. This vibration results earthquakes. If this earth movement is under the sea water, it causes Tsunami.
02. Compression in the earth’s crust:
The rupture in the million tons of water would have hastened the earth’s shaking. No geological process can actually come up with such a huge concentration of mass in such a small area except for a volcano. It is history which has proved of how large reservoirs of water created by dams have caused earthquakes. Examples include from Zambia to Greece and Canada to China. The 2008 Sichuan, China earthquake which killed nearly 70,000 people. It is believed that it was triggered by the construction of the Zipping Dam nearby.
There have been many more examples of Earthquakes in Australia which are believed to be caused by the movements along faults. This could be a result of the compression in the Earth’s crust. You can determine the size or magnitude of earthquakes by measuring the actual amplitude of the seismic waves which gets recorded on a seismograph.
03. Groundwater extraction:
When the ground water is extracted from the Earth it causes the water table to drop thus destabilizing an existing fault. This can a valid reason for an Earthquake. For example, 2011 Lorca earthquake. This 2011 earthquake in Lorca, Spain caused a huge amount of destruction for its 5.1 magnitude as was recorded in the Richter scale. The destruction may be much more severe as the epicenter of the Earthquake is neither so deeper nor away the population.
04. Geothermal drilling causes earthquakes:
Salton Sea Geothermal Field and The Geysers Geothermal Field are the examples of earthquakes caused by geothermal power plants. Seismic activity had increased around the Salton Sea as geothermal field operations around the area had ramped up. While these earthquakes in themselves may not be the main cause of damage but the other interaction with bigger faults like San Andreas could be one. Earthquake swarms include bursts of dozens of small quakes prevailing below magnitude 6 or so—happen regularly along the Salton Sea. Example of such an earthquake include: – Salton Sea Geothermal Field and The Geysers Geothermal Field.
05. Tracking and injection wells:
The process of hydraulic fracturing, or fracking is the only way to extract oil fluid from the earth. The fluid caused due to the extraction of liquids can seep out and also lubricate faults. This can cause them to slip more easily. For example:- 2011 Oklahoma earthquake- A study had pointed out that Seismic activity in Oklahoma has shot up along with the rise of fracking. Earthquake swarms have become a regular occurrence in the region. The number of earthquakes had shot up from a dozen in 2008 to over 1,000 in 2010.
06. Weight of Big and massive buildings:
Big skyscrapers and buildings can put immense pressure on the earth’s surface. It can cause the rudimentary rocks to even crack. As a study points put, that Taipei 101’s especially huge mass of 770,000 tons is presently putting too much pressure on the soft sedimentary rock below. The pressure is further is increased when massive steel and stone is used in the construction of buildings. These massive buildings create an imbalance in the isostatic equilibrium among different parts of earth surface. Moreover these buildings cause cracks and breaks in the rocks. The breaking of these rocks cause earthquakes. But generally this type of Earthquakes is very rare and of low magnitude.
07. Tectonic movements of the earth:
The crust or the outermost shell of the Earth is cracked. The main cause for this crack is the movement of molten mantel which is just beneath the hard crustal shell. Each consolidated part of cracked crust is called Tectonic plate. There are many Tectonic plates namely, Indian Plate, Eurasian Plate, African plate, Antarctic plate, Eurasian plate, Indo-Australian plate, North American plate, Pacific plate and South American plate. Tectonic Earthquakes are caused when the crust becomes subjected to strain, and eventually starts moving. This movement causes Earthquakes. These plates are either moving apart from one another or moving toward one another, or this movement may be transformed. In each case the boundaries posses stress. After severe stress these plates breaks the stress and starts moving. Thus causing an effect of vibration and thrilling resulting earthquakes.
Example: – Due to tectonic movements, San Francisco has noticed many small shakes.
08. Volcanic eruptions:
Volcanic eruption is also a major cause of Earthquakes. Volcanic earthquakes are very less likely than Tectonic ones. Earthquake is triggered whenever there is an explosion of volcanic eruption. The volcanic eruption is quite similar to a powerful bomb blast. This explosion cause vibration in the surface of Earth. The vibration travels all through the Earth depending on its intensity, causing an earthquake.
09. Disturbance on the surface of Earth:
Basically all earthquakes are majorly are the result of disturbance in outer crust on the ephemeral surface of the earth. Anything which will tend to destroy the perfect equilibrium or the balance of the globe will likely cause an earthquake. Each side and every part must necessarily carry the same weight and the state of isostasy must be maintained. Whenever there is a imbalance between two interconnected masses, a movement in the masses may occur. This movement will create disturbance within the surface of Earth, which create vibration and thrilling in the crust, which is known as earthquake.
10. Havoc of a Powerful Bomb Blast:
When ever there is a powerful bomb like thermonuclear bomb detonated, waves of high magnitude are released through the Earth mass. These waves are composed of P-waves, S-wave and L-waves. Although such types of earthquakes are not much destructive, however it can harm weak buildings.
Mainly all types of earthquakes are the result of Elastic Rebound Theory. In each cause of an Earthquake mentioned above the Elastic Rebound Theory is involved. The elastic rebound theory is an explanation for how energy is spread during earthquakes. As rocks on opposite sides of a fault are subjected to force and shift, they accumulate energy and slowly deform until their internal strength is exceeded.
As we know the Earth crust is cracked and broken into pieces like plates and these plates are called Plate Tectonics. Each plate has a boundary with the other. As due to the internal convectional movement of the molten mantel these plates move very slightly. Some plates move in convergence and wrap each other in a way that one plate slides beneath the other. While some plates move apart from each other creating a space between the boundaries of the two divergent plates. This space is again filled by the uprising mantel material. There are also some plates which move transvergetly. This the final type of movement among the plates. The final type of boundary is one where the two plates slide against each other in a sideways motion. These boundaries between plates is referred to as transform boundaries. As two plates slide past one another, in a transform boundary, neither plate is added to at the boundary, nor destroyed. In each type of motion of the plates the chances of Earthquakes are likely. When these boundaries of these plates are so close to each other that movement stop stops for sometime. But the due to the continuous convectional force these plates slips a part all of sudden and a cause intense thrilling. This thrilling creates seismic waves which is actually called and Earthquake. Earthquakes occur all the time all over the world, both along plate edges and along faults.
Most earthquakes occur along the edge of the oceanic and continental plates. The earth’s crust (the outer layer of the planet) is made up of several pieces, called plates. The plates under the oceans are called oceanic plates and the rest are continental plates. The plates are moved around by the motion of a deeper part of the earth (the mantle) that lies underneath the crust. These plates are always bumping into each other, pulling away from each other, or past each other. The plates usually move at about the same speed that your fingernails grow. Earthquakes usually occur where two plates are running into each other or sliding past each other.
AN IMAGE OF THE WORLD’S PLATES AND THEIR BOUNDARIES. NOTICE THAT MANY PLATE BOUNDARIES DO NOT COINCIDE WITH COASTLINES.
A fault is a fracture along which the blocks of crust on either side have moved relative to one another parallel to the fracture. Strike-slip, normal, and reversefaults. A reverse fault with a small dip angle is called a thrust fault.
Earthquakes can also occur far from the edges of plates, along faults. Faults are cracks in the earth where sections of a plate (or two plates) are moving in different directions. Faults are caused by all that bumping and sliding the plates do. They are more common near the edges of the plates.
A normal fault occurs when the crust is extended. Alternatively, such a fault can be called an extensional fault. The hanging wall moves downward, relative to the footwall. A downthrown block between two normal faults dipping towards each other is called a graben.
Normal faults are the cracks where one block of rock is sliding downward and away from another block of rock. These faults usually occur in areas where a plate is very slowly splitting apart or where two plates are pulling away from each other. A normal fault is defined by the hanging wall moving down relative to the footwall, which is moving up.
A NORMAL FAULT. THE ‘FOOTWALL’ IS ON THE ‘UPTHROWN’ SIDE OF THE FAULT, MOVING UPWARDS. THE ‘HANGING WALL’ IS ON THE ‘DOWNTHROWN’ SIDE OF THE FAULT, MOVING DOWNWARDS.
Reverse faults are cracks formed where one plate is pushing into another plate. They also occur where a plate is folding up because it’s being compressed by another plate pushing against it. At these faults, one block of rock is sliding underneath another block or one block is being pushed up over the other. A reverse fault is defined by the hanging wall moving up relative to the footwall, which is moving down.
A REVERSE FAULT. THIS TIME, THE ‘FOOTWALL’ IS ON THE ‘DOWNTHROWN’ SIDE OF THE FAULT, MOVING DOWNWARDS, AND THE ‘HANGING WALL’ IS ON THE ‘UPTHROWN’ SIDE OF THE FAULT, MOVING UPWARDS. WHEN THE HANGING WALL IS ON THE UPTHROWN SIDE, IT ‘HANGS’ OVER THE FOOTWALL.
Strike-slip faults are the cracks between two plates that are sliding past each other. You can find these kinds of faults in California. The San Andreas fault is a strike-slip fault. It’s the most famous California fault and has caused a lot of powerful earthquakes.
TWO STRIKE-SLIP FAULTS. (LEFT), A LEFT-LATERAL STRIKE-SLIP FAULT. NO MATTER WHICH SIDE OF THE FAULT YOU ARE ON, THE OTHER SIDE IS MOVING TO THE LEFT. (RIGHT), A RIGHT-LATERAL STRIKE-SLIP FAULT. NO MATTER WHICH SIDE OF THE FAULT YOU ARE ON, THE OTHER SIDE IS MOVING TO THE RIGHT.
List of Earthquakes Prone Countries
1o Causes of Earthquakes.