How do earthquakes happen? Earthquakes happen when two parts of the surface of the earth suddenly move due to relation with each other along a fault line and due to tectonic forces. Earthquake is basically an unexpected movement of the surface of the earth. Earthquakes are called tectonic earthquakes, when a great amount of energy is released in the form of vibrations and tremors.
What is an earthquake?
An earthquake is defined as the shaking of the earth’s surface which is due to a sudden release of energy in the lithosphere of the earth creating seismic waves. Earthquakes have a different size because some earthquakes are so weak that we cannot feel them and some are violent enough which propell objects and people into the air, and this violence causes destruction across entire cities.
How do earthquakes happen at the surface of the earth? At the surface of the earth, earthquakes occur by shaking and disrupting the ground. A tsunami occurred when the epicenter of a large earthquake is located offshore and the seabed may be displaced sufficiently. Landslides and volcanic activity can also be triggered by earthquakes.
Naturally occurring earthquakes
When there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane in the earth, tectonic earthquakes occur. If there are no irregularities along the fault surface that increase the frictional resistance, the sides of the fault move past each other seismically and smoothly. Most fault surfaces lead to a form of stick-slip behavior. When the fault has locked, the relative motion between the plates continued which leads to increasing stress and stored strain energy in the volume around the fault surface.
The whole process continues until the stress has risen sufficiently to break through the asperity which suddenly allows sliding over the locked portion of the fault and releases the stored energy. This energy is released as a combination of frictional heating of the fault surface, radiated elastic strain seismic waves, and cracking of the rock, that is the reason of how do earthquakes happen. It is estimated that only 10 percent or less of a total energy of earthquake is radiated as seismic energy. Most of the energy of the earthquake is used to convert into heat generated by friction or to power the earthquake fracture growth. Therefore, earthquakes lower the available elastic potential energy of the earth and raise its temperature, though these changes are not noticeable as compared to the conductive and convective flow of heat out from the deep interior of the earth.
Earthquakes and volcanic activity
Most of the earthquakes occur in volcanic regions and are caused there, both by tectonic faults and the magma’s movement in volcanoes. These earthquakes may cause volcanic eruptions, as during the 1980 eruption of Mount St. Helens. Earthquake swarms can serve as markers for the location of the flowing magma throughout the volcanoes. These swarms can be recorded by seismometers and tiltmeters. Seismometers and tiltmeters are the devices that measures ground slope and are used as sensors to predict upcoming eruptions.
What is earthquake explain?
In the explanation of earthquake, I would explain that how do earthquakes happen. Basically, earthquakes happen when two blocks of the earth suddenly slip past one another. The surface where the two blocks slip is called the fault. The hypocenter is the location below the surface of the earth where the earthquake starts, and the epicenter is the location directly above it on the surface of the earth.
An earthquake has sometimes foreshocks. The foreshocks are smaller earthquakes that have the same place to happen as the larger earthquake that follows. The main largest earthquake is called the mainshock. Mainshocks always have aftershocks that follow. Aftershocks are considered as a smaller earthquake that occur afterwards in the same place as the mainshock. Aftershocks can continue for weeks, months, and even years after the mainshock, depending on the size of mainshocks.
Why does the earth shake when there is an earthquake?
While the faults’ edges are stuck together, and the other block is moving, the energy which cause the blocks to slide past one another is being stored up. The stored energy is released in the process of overcoming the friction of the jagged edges by the force of moving blocks. The energy is released from the fault in all sides in the form of seismic waves like ripples on a pond. When they move through it, the seismic waves shake the earth. When the waves reach the surface of the earth, they shake anything on it, like the persons living on it and their houses.
How are earthquakes recorded?
The instruments which record the Earthquakes are called seismographs. The recording that is made by seismographs is called a seismogram. The base of the seismograph and the heavy weight that hangs free is firmly set in the ground. When the ground is shake by earthquake, it causes the base of the seismograph to shake. Instead, the string that it is hanging from absorbs all the movement. The position difference between the shaking part of the seismograph and the immovable part is what is recorded.
Richter scale of earthquake magnitude
| magnitude level | category | effects | |
|---|---|---|---|
| less than 1 to 3 | micro | generally not felt by people, though recorded on local instruments | |
| 3 – 4 | minor | felt by many people; no damage | |
| 4 – 5 | light | felt by all; minor breakage of objects | |
| 5 – 6 | moderate | some damage to weak structures | |
| 6 – 7 | strong | moderate damage in populated areas | |
| 7 – 8 | major | serious damage over large areas; loss of life | |
| 8 and higher | great | severe destruction and loss of life over large areas |
Earthquake causes
Many of the people don’t know the exact reason of how do earthquakes happen. The earthquakes occur on earth mainly in belts which coincide with the margins of tectonic plates. This has long been reflected in the catalogs of the earthquake, and is easily seen on modern seismicity maps, which show epicenters determined by instruments. Circum-Pacific Belt is the most important belt of the earthquake, which covers most of the densely populated coastal areas of the Pacific Ocean, for example, those in New Zealand, New Guinea, Japan, the Aleutian Islands, Alaska, and the western parts of North and South America.
It is estimated that 80 percent of the energy released by earthquakes now comes from those with epicenters in this belt. The seismic activity is not same throughout the belt, and there are many branches in different points. Because in many places the Circum-Pacific Belt is associated with a volcano, it has been dubbed the “Pacific Ring of Fire.”
The Alpide Belt, passes through the eastern Mediterranean region through Asia and joins the Circum-Pacific Belt in the East Indies. Earthquake energy in this belt is about 15 percent of the world’s total. There are also striking connected belts for seismic activity, particularly along the oceanic ridges, which include those in the Arctic Ocean, the Atlantic Ocean, and the western Indian Ocean as well as the rift valleys of East Africa. This distribution of seismicity around the world is better understood in terms of its tectonic plate arrangement.
Earthquake effects
Following is mentioned some effects of earthquake which include ground shaking, surface faulting, ground failure, and less commonly, tsunamis.
Ground Shaking
It is a term which is mainly used to explain how do earthquakes happen. Ground shaking is caused by body waves and surface waves. As a general practice, the severity of the ground shaking increases as the size increases and decreases as the distance from the causative fault increases. Although the physics of seismic waves are complex, ground shaking can be defined in terms of body waves, compression, or P, and shear, or S, and surface waves, Rayleigh and Love.
P waves propagate on Earth at a speed of about 15,000 miles per hour and are the first waves which could be the cause of earthquake. S waves come next and cause the structure to vibrate from one side to the other. They are the most damaging waves, for buildings are more easily damaged by horizontal movement than by vertical movement. P and S waves cause the high frequency vibrations; meanwhile, Rayleigh’s waves and Love’s waves, cause low-frequency vibrations. The waves of the body and face cause the earth, and as a result the building, it vibrates in a complex way. The purpose of an earthquake-resistant structure is to build a structure that can withstand the ground shaking caused by body waves and surface waves.
In land use zoning and resistant design of earthquake, amplitude information, frequency formation, and ground shaking time are required. These issues can be determined by visual (empirical) data linking the magnitude and distribution of the Modified Mercalli earthquake intensity, the distance from the building from the causative fault, and the physical properties of the soil and rock underlying the building. The numerical value of the Modified Mercalli Intensity Scale indicates the Ground shaking’s effect on a person, on buildings and on the surface of the earth.
When a fault erupts, seismic waves are spread in all directions, causing the earth to vibrate at frequencies ranging from 0.1 to 30 Hertz. Buildings vibrate due to ground shaking; damage occurs if the structure cannot withstand this movement. Compressional waves and shear waves in particular cause high frequency vibrations (greater than 1 Hertz) which are more efficient than low frequency waves causing low-level vibrations. Rayleigh’s and love waves cause low-frequency vibrations that work much better than high-frequency waves causing tall buildings to vibrate. Because low-frequency vibration amplitudes decompose faster than high-frequency vibration as the distance from fault increases, tall buildings located at a great distance (60 miles) from fault will sometimes be damaged.
Surface Faulting
It is the differential movement of the different sides of a fracture at the surface of the earth and can be strike-slip, normal, and reverse. combinations of the strike-slip type and the other two kinds of faulting can be found. Despite the fact that displacement of these types can result from landslides and other shallow cycles, surface faulting applies to differential movements brought about by deep-seated forces in the Earth, sedimentary deposit’s slow movement toward the Gulf of Mexico, and faulting related with salt domes.
Injuries and death caused by surface faulting are impossible, yet casualties can happen through fault damage to structures. Surface faulting, on account of a strike-slip fault, generally influences a long narrow zone whose total area is little compared with the complete area influenced by ground shaking. In any case, the damage to structures situated in the fault zone can be high, particularly where the land use is intensive. A variety of structures have been damaged by surface faulting, including apartments, houses, commercial buildings, nursing homes, railways, highways, burrows, bridges, channels, storm drains, water wells, and water, gas, and sewer lines. Damage to these types of structures has gone from minor to exceptionally severe. An illustration of extreme damage happened in 1952 when three railroad tunnels were so severely harmed by faulting that traffic on a significant rail connecting northern and southern California was stopped for 25 days despite an around-the-clock repair schedule.
The lengths, displacements and widths of surface faulting ruptures show a wide range. Fault displacements in the United States have ranged from a small portion of an inch to in excess of 20 feet of differential movement. The severity of potential harm increments as the size of the displacement increases. The lengths of the surface fault rupture on land have ranged from under 1 mile to more than 200 miles. Most of the fault displacements is limited to a narrow zone going from 6 to 1,000 feet in width, yet separate subsidiary fault ruptures may happen 2 to 3 miles from the primary fault. The territory subject to disruption by surface faulting changes with the length and width of the rupture zone.
Ground Failure
Liquefaction isn’t a kind of ground failure; it is a physical process that happens during certain earthquakes that may prompt ground failure. As a result of liquefaction, clay free soil deposits, fundamentally sands and sediments, temporarily lose strength and carry on as viscous fluids instead of as solids. Liquefaction happens when seismic shear waves go through an immersed granular soil layer, distort its granular structure, and cause a portion of the void spaces to collapse. Disruptions to the soil created by these collapses cause transfer of the ground-shaking load from grain-to-grain contacts in the soil layer to the pore water. This exchange of load increases pressure in the pore water, either making drainage to happen or, if drainage is confined, an abrupt development of pore-water pressure. At the point when the pore-water pressure ascends to about the pressure brought about by the weight of the column of soil, the granular soil layer carries on like a liquid instead of like a solid for a brief period. In this condition, deformation can happen without any problem.
Liquefaction is confined to certain geologic and hydrologic conditions, especially areas where sands and residues were deposited over the most recent 10,000 years and where ground water is inside 30 feet of the surface. For the most part, the younger and looser the residue and the higher the water table, the more susceptible a soil is to liquefaction.
Liquefaction causes three kinds of ground failure: lateral spreads, flow failures, and loss of bearing strength. Moreover, liquefaction improves ground settlement and sometimes creates sand boils. Sand boils can cause flooding and the deposition of silt.
Lateral Spreads include the lateral movement of large blocks of soil because of liquefaction in a subsurface layer. Movement happens in light of the ground shaking produced by an earthquake. Lateral spreads create on gentle inclines, most generally on those somewhere in the range of 0.3 and 3 degrees. Horizontal movements on lateral spreads generally are just about as much as 10 to 15 feet, but, where slopes are especially favorable and the term of ground shaking is long, lateral movement might be pretty much as much as 100 to 150 feet. Lateral spreads typically separate inside, shaping various fissures and scarps.
Damage brought about by lateral spreads is sometimes cataclysmic, however it is generally troublesome. For instance, during the 1964 Prince William Sound, Alaska, tremor, in excess of 200 bridges were damaged by parallel spreading of flood-plain deposits toward stream channels. These spreading deposits compressed bridges over the channels, clasped decks, push sedimentary beds over abutments, and tilted and shifted piers and abutments.
Lateral spreads are ruinous especially to pipelines. In 1906, various significant pipeline breaks happened in the city of San Francisco during the earthquake as a result of lateral spreading. Breaks of water mains hampered endeavors to fight the fire that lighted during the earthquake. In this way, maybe unnoticeable ground-failure displacements of less over 7 feet were to a great extent responsible for the destruction to San Francisco in 1906.
Tsunamis
Tsunami are water waves that are produced by the abrupt vertical movement of the large area of a sea floor during an undersea earthquake. Tidal waves are frequently called tsunamis; however, this term is a misnomer. Dissimilar to regular ocean tides, tsunamis are not brought about by the tidal action of the Moon and Sun. The tsunami’s height in the deep ocean is around 1 foot, yet the distance between wave crests can be extremely long, in excess of 60 miles. The speed at which the tsunami voyages decline as water depth diminishes. In the mid-Pacific, where the water depths reach 3 miles, tsunami speeds can be in excess of 430 miles each hour. As tsunami arrive at shallow water around islands or on a continental shelf; the height of the waves increases commonly, sometimes coming to as much as 80 feet. The significant distance between wave crests keeps waves from disseminating energy as a breaking surf; all things being equal, tsunami cause water levels to rise quickly along coast lines.
Earthquakes and tsunami ground shaking vary in their destructive characteristics. Ground shaking causes destruction chiefly in the vicinity of the causative fault, yet tsunamis cause obliteration both locally and at exceptionally far off areas from the area of tsunami generation.
Frequently Asked Questions
Following is mentioned some frequently asked questions related to how do earthquakes happen, which are answered briefly:
1. Do humans cause earthquakes?
Yes, some minor earthquakes caused by the activity of humans. Induced seismicity refers to typically minor earthquakes and tremors that are caused by human activity that alters the strains and stresses on the crust of the earth.
2. What are the 4 types of earthquakes?
There are four different types of earthquakes:
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Tectonic
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Volcanic
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Collapse
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A tectonic earthquake occurs when the crust of the earth breaks due to geological forces on rocks and adjoining plates that cause chemical and physical changes.
3. Can you feel a 1.0 earthquake?
Normally, we cannot feel a 1.0 earthquake. A minor earthquake far away will probably not be felt at all, but if someone it, it will be a subtle gentle shake or two that can be easily felt if you’re in a still position and sitting down.
4. Can we prevent earthquake?
We can significantly mitigate their effects by identifying hazards, building safer structures, and providing education on earthquake safety but it is not in a human control to prevent natural earthquakes at all. We can also reduce the risk from human induced earthquakes by preparing for natural earthquakes.
5. How far away can you feel a 9.0 earthquake?
In a place with complex geology, each rock contact disperses and assimilates seismic energy, so that distant you’d most likely feel it however not see casualties or damage. In the U.S. Midcontinent, with layer-cake geology that makes proficient wave guides, a 9.0 event would most likely produce apparent damage 565 miles away.
6. What is the most dangerous type of earthquake?
Love waves are the most dangerous of all kinds of seismic waves are the Love waves. Love waves are faster than Rayleigh waves and these waves are even larger in amplitude.
7. How can we prevent earthquake damage at home?
Following are the ways which could help you to prevent earthquake damage at home:
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Shelter in place
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Cover your head
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Crawl under sturdy furniture such as a heavy desk or table, or against an inside wall
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Stay away from where glass could shatter around windows, mirrors, pictures, or where heavy bookcases or other heavy furniture could fall over.
8. Can we predict earthquakes?
Yes, we it can be possible to predict earthquakes. Most scientists are pessimistic and believe that prediction might be possible and some maintain that earthquake prediction is inherently impossible.
9. Where are there no earthquakes?
There is no any place in the world that doesn’t have earthquakes. Florida and North Dakota are those states that have fewest earthquakes. Antarctica has the least earthquakes of any continent, but small earthquakes can occur anywhere in the World.
10. What are the 5 largest earthquakes ever recorded?
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Valdivia, Chile, 22 May 1960 (9.5)
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Prince William Sound, Alaska, 28 March 1964 (9.2)
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Sumatra, Indonesia, 26 December 2004 (9.1)
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Sendai, Japan, 11 March 2011 (9.0)
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Kamchatka, Russia, 4 November 1952 (9.0)
Conclusion 
This article tells the complete information about how do earthquakes happen. Earthquakes usually happen when rock under the earth suddenly breaks along a fault. The energy releases during this process causes the seismic waves that make the ground shake.
