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An earthquakealso called a quake, tremor, or tembloris the shaking of the
Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
's surface resulting from a sudden release of energy in the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...
that creates
seismic wave A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large ma ...
s. Earthquakes can range in
intensity Intensity may refer to: In colloquial use * Strength (disambiguation) *Amplitude * Level (disambiguation) * Magnitude (disambiguation) In physical sciences Physics *Intensity (physics), power per unit area (W/m2) *Field strength of electric, m ...
, from those so weak they cannot be felt, to those violent enough to propel objects and people into the air, damage critical infrastructure, and wreak destruction across entire cities. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The
seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 194 ...
at a particular location in the Earth is the average rate of seismic energy release per unit volume. In its most general sense, the word ''earthquake'' is used to describe any seismic event that generates seismic waves. Earthquakes can occur naturally or be induced by human activities, such as
mining Mining is the Resource extraction, extraction of valuable geological materials and minerals from the surface of the Earth. Mining is required to obtain most materials that cannot be grown through agriculture, agricultural processes, or feasib ...
,
fracking Fracking (also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of formations in bedrock by a pressurized liquid. The process involves the high-pressure inje ...
, and
nuclear weapons testing Nuclear weapons tests are experiments carried out to determine the performance of nuclear weapons and the effects of Nuclear explosion, their explosion. Nuclear testing is a sensitive political issue. Governments have often performed tests to si ...
. The initial point of rupture is called the
hypocenter A hypocenter or hypocentre (), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its ...
or focus, while the ground level directly above it is the
epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...
. Earthquakes are primarily caused by geological faults, but also by
volcanism Volcanism, vulcanism, volcanicity, or volcanic activity is the phenomenon where solids, liquids, gases, and their mixtures erupt to the surface of a solid-surface astronomical body such as a planet or a moon. It is caused by the presence of a he ...
, landslides, and other seismic events. Significant historical earthquakes include the
1556 Shaanxi earthquake The 1556 Shaanxi earthquake ( Postal romanization: ''Shensi''), known in Chinese colloquially by its regnal year as the Jiajing Great Earthquake "" ('' Jiājìng Dàdìzhèn'') or officially by its epicenter as the Hua County Earthquake "" ('' ...
in China, with over 830,000 fatalities, and the
1960 Valdivia earthquake The 1960 Valdivia earthquake and tsunami () or the Great Chilean earthquake (''Gran terremoto de Chile'') occurred on 22 May 1960. Most studies have placed it at 9.5–9.6 on the moment magnitude scale, while some studies have placed the magnitu ...
in Chile, the largest ever recorded at 9.5 magnitude. Earthquakes result in various effects, such as ground shaking and
soil liquefaction Soil liquefaction occurs when a cohesionless saturated or partially saturated soil substantially loses Shear strength (soil), strength and stiffness in response to an applied Shear stress, stress such as shaking during an earthquake or other s ...
, leading to significant damage and loss of life. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a
tsunami A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, ...
. Earthquakes can trigger
landslide Landslides, also known as landslips, rockslips or rockslides, are several forms of mass wasting that may include a wide range of ground movements, such as rockfalls, mudflows, shallow or deep-seated slope failures and debris flows. Landslides ...
s. Earthquakes' occurrence is influenced by
tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...
movements along faults, including normal, reverse (thrust), and strike-slip faults, with energy release and rupture dynamics governed by the
elastic-rebound theory __NOTOC__ In geology, the elastic-rebound theory is an explanation for how energy is released during an earthquake. As the Earth's crust deforms, the rocks which span the opposing sides of a fault are subjected to shear stress. Slowly they de ...
. Efforts to manage earthquake risks involve prediction, forecasting, and preparedness, including
seismic retrofit Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...
ting and earthquake engineering to design structures that withstand shaking. The cultural impact of earthquakes spans myths, religious beliefs, and modern media, reflecting their profound influence on human societies. Similar seismic phenomena, known as
marsquake A marsquake is a Quake (natural phenomenon), quake which, much like an earthquake, is a shaking of the surface or interior of the planet Mars. Such quakes may occur with a shift in the planet's interior, such as the result of plate tectonics, from ...
s and
moonquakes A quake is the result when the surface of a planet, moon or star begins to shake, usually as the consequence of a sudden release of energy transmitted as seismic waves, and potentially with great violence. The types of quakes include earthquake, ...
, have been observed on other celestial bodies, indicating the universality of such events beyond Earth.


Terminology

An earthquake is the shaking of the surface of
Earth Earth is the third planet from the Sun and the only astronomical object known to Planetary habitability, harbor life. This is enabled by Earth being an ocean world, the only one in the Solar System sustaining liquid surface water. Almost all ...
resulting from a sudden release of energy in the
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...
that creates
seismic wave A seismic wave is a mechanical wave of acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake), volcanic eruption, magma movement, a large landslide and a large ma ...
s. Earthquakes may also be referred to as ''quakes'', ''tremors'', or ''temblors''. The word ''tremor'' is also used for non-earthquake seismic rumbling. In its most general sense, an ''earthquake'' is any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by the rupture of geological faults but also by other events such as volcanic activity, landslides, mine blasts,
fracking Fracking (also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of formations in bedrock by a pressurized liquid. The process involves the high-pressure inje ...
and
nuclear tests Nuclear weapons tests are experiments carried out to determine the performance of nuclear weapons and the effects of Nuclear explosion, their explosion. Nuclear testing is a sensitive political issue. Governments have often performed tests to si ...
. An earthquake's point of initial rupture is called its
hypocenter A hypocenter or hypocentre (), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its ...
or focus. The
epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...
is the point at ground level directly above the hypocenter. The seismic activity of an area is the frequency, type, and size of earthquakes experienced over a particular time. The
seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 194 ...
at a particular location in the Earth is the average rate of seismic energy release per unit volume.


Major examples

One of the most devastating earthquakes in recorded history was the
1556 Shaanxi earthquake The 1556 Shaanxi earthquake ( Postal romanization: ''Shensi''), known in Chinese colloquially by its regnal year as the Jiajing Great Earthquake "" ('' Jiājìng Dàdìzhèn'') or officially by its epicenter as the Hua County Earthquake "" ('' ...
, which occurred on 23 January 1556 in
Shaanxi Shaanxi is a Provinces of China, province in north Northwestern China. It borders the province-level divisions of Inner Mongolia to the north; Shanxi and Henan to the east; Hubei, Chongqing, and Sichuan to the south; and Gansu and Ningxia to t ...
, China. More than 100,000 people died, with the region losing up to 830,000 people afterwards due to emmigration, plague, and famine. Most houses in the area were
yaodong A yaodong (窰 in native Jin Chinese, or 窰洞 ''yáodòng'' in Beijing Mandarin) is a particular form of Earth sheltering, earth shelter dwelling common in the Loess Plateau in China's north. They are generally carved out of a hillside or exc ...
s—dwellings carved out of
loess A loess (, ; from ) is a clastic rock, clastic, predominantly silt-sized sediment that is formed by the accumulation of wind-blown dust. Ten percent of Earth's land area is covered by loesses or similar deposition (geology), deposits. A loess ...
hillsides—and many victims were killed when these structures collapsed. The
1976 Tangshan earthquake The 1976 Tangshan earthquake () was a 7.6 earthquake that hit the region around Tangshan, Hebei, China, at 3:42 a.m. on 28 July 1976. The maximum intensity of the earthquake was XI (''Extreme'') on the Mercalli intensity scale, Mercalli sca ...
, which killed between 240,000 and 655,000 people, was the deadliest of the 20th century. The
1960 Chilean earthquake The 1960 Valdivia earthquake and tsunami () or the Great Chilean earthquake (''Gran terremoto de Chile'') occurred on 22 May 1960. Most studies have placed it at 9.5–9.6 on the moment magnitude scale, while some studies have placed the magnitu ...
is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960. Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday earthquake (27 March 1964), which was centered in
Prince William Sound Prince William Sound ( Sugpiaq: ''Suungaaciq'') is a sound off the Gulf of Alaska on the south coast of the U.S. state of Alaska. It is located on the east side of the Kenai Peninsula. Its largest port is Valdez, at the southern terminus of the ...
, Alaska. The ten largest recorded earthquakes have all been
megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthq ...
s; however, of these ten, only the
2004 Indian Ocean earthquake On 26 December 2004, at 07:58:53 local time (UTC+07:00, UTC+7), a major earthquake with a magnitude of 9.2–9.3 struck with an epicenter, epicentre off the west coast of Aceh in northern Sumatra, Indonesia. The Submarine earthquake, undersea ...
is simultaneously one of the deadliest earthquakes in history. Earthquakes that caused the greatest loss of life, while powerful, were deadly because of their proximity to either heavily populated areas or the ocean, where earthquakes often create
tsunamis A tsunami ( ; from , ) is a series of waves in a water body caused by the displacement of a large volume of water, generally in an ocean or a large lake. Earthquakes, volcanic eruptions and underwater explosions (including detonations, la ...
that can devastate communities thousands of kilometers away. Regions most at risk for great loss of life include those where earthquakes are relatively rare but powerful, and poor regions with lax, unenforced, or nonexistent seismic building codes.


Occurrence

Tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...
earthquakes occur anywhere on the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or
asperities In materials science, asperity, defined as "unevenness of surface, roughness, ruggedness" (from the Latin ''asper''—"rough"), has implications (for example) in physics and seismology. Smooth surfaces, even those polished to a mirror finish, ar ...
along the fault surface that increases the frictional resistance. Most fault surfaces do have such asperities, which leads to a form of stick-slip behavior. Once the fault has locked, continued relative motion between the plates leads to increasing stress and, therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain
seismic waves A seismic wave is a mechanical wave of acoustic wave, acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake (natural phenomenon), quake), types of volcanic eruptions ...
, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the
elastic-rebound theory __NOTOC__ In geology, the elastic-rebound theory is an explanation for how energy is released during an earthquake. As the Earth's crust deforms, the rocks which span the opposing sides of a fault are subjected to shear stress. Slowly they de ...
. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake
fracture Fracture is the appearance of a crack or complete separation of an object or material into two or more pieces under the action of stress (mechanics), stress. The fracture of a solid usually occurs due to the development of certain displacemen ...
growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available
elastic potential energy Elastic energy is the mechanical potential energy stored in the configuration of a material or physical system as it is subjected to elastic deformation by work performed upon it. Elastic energy occurs when objects are impermanently compressed, s ...
and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.


Fault types

There are three main types of fault, all of which may cause an
interplate earthquake An interplate earthquake occurs at the boundary between two tectonic plates. Earthquakes of this type account for more than 90 percent of the total seismic energy released around the world. If one plate is trying to move past the other, they will ...
: normal, reverse (thrust), and strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and where movement on them involves a vertical component. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip. The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending into the hot mantle, are the only parts of our planet that can store elastic energy and release it in fault ruptures. Rocks hotter than about flow in response to stress; they do not rupture in earthquakes. The maximum observed lengths of ruptures and mapped faults (which may break in a single rupture) are approximately . Examples are the earthquakes in Alaska (1957), Chile (1960), and Sumatra (2004), all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the
San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...
(
1857 Events January–March * January 1 – The biggest Estonian newspaper, '' Postimees'', is established by Johann Voldemar Jannsen. * January 7 – The partly French-owned London General Omnibus Company begins operating. * Ja ...
,
1906 Events January–February * January 12 – Persian Constitutional Revolution: A nationalistic coalition of merchants, religious leaders and intellectuals in Persia forces the shah Mozaffar ad-Din Shah Qajar to grant a constitution, ...
), the
North Anatolian Fault The North Anatolian Fault (NAF; ) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian plate and the Anatolian sub-plate. The fault extends westward from a junction with the Ea ...
in Turkey (
1939 This year also marks the start of the World War II, Second World War, the largest and deadliest conflict in human history. Events Events related to World War II have a "WWII" prefix. January * January 1 ** Coming into effect in Nazi Ger ...
), and the
Denali Fault The Denali Fault is a major intracontinental dextral (right lateral) Fault (geology)#Strike-slip faults, strike-slip fault in western North America, extending from northwestern British Columbia, Canada to the central region of the U.S. state of ...
in Alaska (
2002 The effects of the September 11 attacks of the previous year had a significant impact on the affairs of 2002. The war on terror was a major political focus. Without settled international law, several nations engaged in anti-terror operation ...
), are about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.


Normal faults

Normal faults occur mainly in areas where the crust is being extended such as a
divergent boundary In plate tectonics, a divergent boundary or divergent plate boundary (also known as a constructive boundary or an extensional boundary) is a linear feature that exists between two List of tectonic plates, tectonic plates that are moving away fr ...
. Earthquakes associated with normal faults are generally less than magnitude 7. Maximum magnitudes along many normal faults are even more limited because many of them are located along spreading centers, as in Iceland, where the thickness of the brittle layer is only about .


Reverse faults

Reverse faults occur in areas where the crust is being shortened such as at a
convergent boundary A convergent boundary (also known as a destructive boundary) is an area on Earth where two or more lithospheric plates collide. One plate eventually slides beneath the other, a process known as subduction. The subduction zone can be defined by a ...
. Reverse faults, particularly those along convergent boundaries, are associated with the most powerful earthquakes (called
megathrust earthquake Megathrust earthquakes occur at convergent plate boundaries, where one tectonic plate is forced underneath another. The earthquakes are caused by slip along the thrust fault that forms the contact between the two plates. These interplate earthq ...
s) including almost all of those of magnitude 8 or more. Megathrust earthquakes are responsible for about 90% of the total seismic moment released worldwide.


Strike-slip faults

Strike-slip fault In geology, a fault is a planar fracture or discontinuity in a volume of rock across which there has been significant displacement as a result of rock-mass movements. Large faults within Earth's crust result from the action of plate tectonic ...
s are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Strike-slip faults, particularly continental transforms, can produce major earthquakes up to about magnitude 8. Strike-slip faults tend to be oriented near vertically, resulting in an approximate width of within the brittle crust. Thus, earthquakes with magnitudes much larger than 8 are not possible. In addition, there exists a hierarchy of stress levels in the three fault types. Thrust faults are generated by the highest, strike-slip by intermediate, and normal faults by the lowest stress levels. This can easily be understood by considering the direction of the greatest principal stress, the direction of the force that "pushes" the rock mass during the faulting. In the case of normal faults, the rock mass is pushed down in a vertical direction, thus the pushing force (''greatest'' principal stress) equals the weight of the rock mass itself. In the case of thrusting, the rock mass "escapes" in the direction of the least principal stress, namely upward, lifting the rock mass, and thus, the overburden equals the ''least'' principal stress. Strike-slip faulting is intermediate between the other two types described above. This difference in stress regime in the three faulting environments can contribute to differences in stress drop during faulting, which contributes to differences in the radiated energy, regardless of fault dimensions.


Energy released

For every unit increase in seismic magnitude, there is a roughly thirty-fold increase in the energy released. For instance, an earthquake of magnitude 6.0 releases approximately 32 times as much energy as an earthquake of magnitude 5.0, and a 7.0 magnitude earthquake releases about 1,000 times as much energy as a 5.0 magnitude earthquake. An 8.6-magnitude earthquake releases the same amount of energy as 10,000 atomic bombs of the size used in
World War II World War II or the Second World War (1 September 1939 – 2 September 1945) was a World war, global conflict between two coalitions: the Allies of World War II, Allies and the Axis powers. World War II by country, Nearly all of the wo ...
. This is so because the energy released in an earthquake, and thus its magnitude, is proportional to the area of the fault that ruptures and the stress drop. Therefore, the greater the length and width of the faulted area, the greater the resulting magnitude. The most important parameter controlling the maximum earthquake magnitude on a fault, however, is not the maximum available length, but the available width because the latter varies by a factor of 20. Along converging plate margins, the dip angle of the rupture plane is very shallow, typically about 10 degrees. Thus, the width of the plane within the top brittle crust of the Earth can reach (such as in Japan, 2011, or in Alaska, 1964), making the most powerful earthquakes possible.


Focus

The majority of tectonic earthquakes originate in the Ring of Fire at depths not exceeding tens of kilometers. Earthquakes occurring at depths less than are classified as "shallow-focus" earthquakes, while those with focal depths between are commonly termed "mid-focus" or "intermediate-depth" earthquakes. In
subduction Subduction is a geological process in which the oceanic lithosphere and some continental lithosphere is recycled into the Earth's mantle at the convergent boundaries between tectonic plates. Where one tectonic plate converges with a second p ...
zones, where older and colder
oceanic crust Oceanic crust is the uppermost layer of the oceanic portion of the tectonic plates. It is composed of the upper oceanic crust, with pillow lavas and a dike complex, and the lower oceanic crust, composed of troctolite, gabbro and ultramaf ...
descends beneath another tectonic plate,
deep-focus earthquake A deep-focus earthquake in seismology (also called a plutonic earthquake) is an earthquake with a hypocenter depth exceeding 300 km. They occur almost exclusively at convergent boundaries in association with subducted oceanic lithosphere. ...
s may occur at much greater depths (ranging from ). These seismically active areas of subduction are known as
Wadati–Benioff zone A Wadati–Benioff zone (also Benioff–Wadati zone or Benioff zone or Benioff seismic zone) is a planar zone of seismicity corresponding with the down-going slab in a subduction zone. Differential motion along the zone produces numerous earth ...
s. Deep-focus earthquakes occur at depths where the subducted
lithosphere A lithosphere () is the rigid, outermost rocky shell of a terrestrial planet or natural satellite. On Earth, it is composed of the crust and the lithospheric mantle, the topmost portion of the upper mantle that behaves elastically on time ...
should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep-focus earthquakes is faulting caused by
olivine The mineral olivine () is a magnesium iron Silicate minerals, silicate with the chemical formula . It is a type of Nesosilicates, nesosilicate or orthosilicate. The primary component of the Earth's upper mantle (Earth), upper mantle, it is a com ...
undergoing a
phase transition In physics, chemistry, and other related fields like biology, a phase transition (or phase change) is the physical process of transition between one state of a medium and another. Commonly the term is used to refer to changes among the basic Sta ...
into a
spinel Spinel () is the magnesium/aluminium member of the larger spinel group of minerals. It has the formula in the cubic crystal system. Its name comes from the Latin word , a diminutive form of ''spine,'' in reference to its pointed crystals. Prop ...
structure.


Volcanic activity

Earthquakes often occur in volcanic regions and are caused there, both by
tectonic Tectonics ( via Latin ) are the processes that result in the structure and properties of the Earth's crust and its evolution through time. The field of ''planetary tectonics'' extends the concept to other planets and moons. These processes ...
faults and the movement of
magma Magma () is the molten or semi-molten natural material from which all igneous rocks are formed. Magma (sometimes colloquially but incorrectly referred to as ''lava'') is found beneath the surface of the Earth, and evidence of magmatism has also ...
in
volcano A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most oft ...
es. Such earthquakes can serve as an early warning of volcanic eruptions, as during the
1980 eruption of Mount St. Helens In March 1980, a series of volcanic explosions and pyroclastic flows began at Mount St. Helens in Skamania County, Washington, United States. A series of Phreatic eruption, phreatic blasts occurred from the summit and escalated until a major ...
. Earthquake swarms can serve as markers for the location of the flowing magma throughout the volcanoes. These swarms can be recorded by
seismometers A seismometer is an instrument that responds to ground displacement and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The outp ...
and
tiltmeter A tiltmeter is a sensitive inclinometer designed to measure very small changes from the vertical level, either on the ground or in structures. Tiltmeters are used extensively for monitoring volcanoes, the response of dams to filling, the small ...
s (a device that measures ground slope) and used as sensors to predict imminent or upcoming eruptions.


Rupture dynamics

A tectonic earthquake begins as an area of initial slip on the fault surface that forms the focus. Once the rupture has been initiated, it begins to propagate away from the focus, spreading out along the fault surface. Lateral propagation will continue until either the rupture reaches a barrier, such as the end of a fault segment, or a region on the fault where there is insufficient stress to allow continued rupture. For larger earthquakes, the depth extent of rupture will be constrained downwards by the brittle-ductile transition zone and upwards by the ground surface. The mechanics of this process are poorly understood because it is difficult either to recreate such rapid movements in a laboratory or to record seismic waves close to a nucleation zone due to strong ground motion. In most cases, the rupture speed approaches, but does not exceed, the
shear wave __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because t ...
(S wave) velocity of the surrounding rock. There are a few exceptions to this:


Supershear earthquakes

Supershear earthquake In seismology, a supershear earthquake is when the propagation of the Earthquake rupture, rupture along the Fault (geology), fault surface occurs at speeds in excess of the seismic S wave, shear wave (S wave) velocity. This causes an effect analo ...
ruptures are known to have propagated at speeds greater than the S wave velocity. These have so far all been observed during large strike-slip events. The unusually wide zone of damage caused by the
2001 Kunlun earthquake 1 (one, unit, unity) is a number, numeral, and glyph. It is the first and smallest positive integer of the infinite sequence of natural numbers. This fundamental property has led to its unique uses in other fields, ranging from science to sp ...
has been attributed to the effects of the
sonic boom A sonic boom is a sound associated with shock waves created when an object travels through the air faster than the speed of sound. Sonic booms generate enormous amounts of sound energy, sounding similar to an explosion or a thunderclap to ...
developed in such earthquakes.


Slow earthquakes

Slow earthquake A slow earthquake, also known as a silent earthquake, is a discontinuous, earthquake-like event that releases energy over a period of hours to months, rather than the seconds to minutes characteristic of a typical earthquake. First detected using ...
ruptures travel at unusually low velocities. A particularly dangerous form of slow earthquake is the
tsunami earthquake In seismology, a tsunami earthquake is an earthquake which triggers a tsunami of significantly greater Seismic magnitude scales, magnitude, as measured by shorter-period seismic waves. The term was introduced by Japanese seismologist Hiroo Kanam ...
, observed where the relatively low felt intensities, caused by the slow propagation speed of some great earthquakes, fail to alert the population of the neighboring coast, as in the
1896 Sanriku earthquake The was one of the most destructive seismic events in Japanese history. The 8.5 magnitude earthquake occurred at 19:32 (local time) on June 15, 1896, approximately off the coast of Iwate Prefecture, Honshu. It resulted in two tsunami waves whic ...
.


Co-seismic overpressuring and effect of pore pressure

During an earthquake, high temperatures can develop at the fault plane, increasing pore pressure and consequently vaporization of the groundwater already contained within the rock. In the coseismic phase, such an increase can significantly affect slip evolution and speed, in the post-seismic phase it can control the
Aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in Epicenter, the same area of the Mainshock, main shock, caused as the displaced Crust (geology), crust adjusts to the effects of the main shock. Large earthq ...
sequence because, after the main event, pore pressure increase slowly propagates into the surrounding fracture network. From the point of view of the Mohr-Coulomb strength theory, an increase in fluid pressure reduces the normal stress acting on the fault plane that holds it in place, and fluids can exert a lubricating effect. As thermal overpressurization may provide positive feedback between slip and strength fall at the fault plane, a common opinion is that it may enhance the faulting process instability. After the mainshock, the pressure gradient between the fault plane and the neighboring rock causes a fluid flow that increases pore pressure in the surrounding fracture networks; such an increase may trigger new faulting processes by reactivating adjacent faults, giving rise to aftershocks. Analogously, artificial pore pressure increase, by fluid injection in Earth's crust, may induce seismicity.


Tidal forces

Tides Tides are the rise and fall of sea levels caused by the combined effects of the gravitational forces exerted by the Moon (and to a much lesser extent, the Sun) and are also caused by the Earth and Moon orbiting one another. Tide tables ...
may trigger some
seismicity Seismicity is a measure encompassing earthquake occurrences, mechanisms, and magnitude at a given geographical location. As such, it summarizes a region's seismic activity. The term was coined by Beno Gutenberg and Charles Francis Richter in 194 ...
.


Clusters

Most earthquakes form part of a sequence, related to each other in terms of location and time. Most earthquake clusters consist of small tremors that cause little to no damage, but there is a theory that earthquakes can recur in a regular pattern. Earthquake clustering has been observed, for example, in Parkfield, California where a long-term research study is being conducted around the
Parkfield earthquake Parkfield earthquake is a name given to various large earthquakes that occurred in the vicinity of the town of Parkfield, California, United States. The San Andreas fault runs through this town, and six successive magnitude 6 earthquakes occurre ...
cluster.


Aftershocks

An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. Rapid changes of stress between rocks, and the stress from the original earthquake are the main causes of these aftershocks, along with the crust around the ruptured fault plane as it adjusts to the effects of the mainshock. An aftershock is in the same region as the main shock but always of a smaller magnitude, however, they can still be powerful enough to cause even more damage to buildings that were already previously damaged from the mainshock. If an aftershock is larger than the mainshock, the aftershock is redesignated as the mainshock and the original main shock is redesignated as a
foreshock A foreshock is an earthquake that occurs before a larger seismic eventthe mainshockand is related to it in both time and space. The designation of an earthquake as ''foreshock'', ''mainshock'' or aftershock is only possible after the full sequenc ...
. Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the mainshock.


Swarms

Earthquake swarms are sequences of earthquakes striking in a specific area within a short period. They are different from earthquakes followed by a series of
aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in Epicenter, the same area of the Mainshock, main shock, caused as the displaced Crust (geology), crust adjusts to the effects of the main shock. Large earthq ...
s by the fact that no single earthquake in the sequence is the main shock, so none has a notably higher magnitude than another. An example of an earthquake swarm is the 2004 activity at
Yellowstone National Park Yellowstone National Park is a List of national parks of the United States, national park of the United States located in the northwest corner of Wyoming, with small portions extending into Montana and Idaho. It was established by the 42nd U ...
. In August 2012, a swarm of earthquakes shook
Southern California Southern California (commonly shortened to SoCal) is a geographic and Cultural area, cultural List of regions of California, region that generally comprises the southern portion of the U.S. state of California. Its densely populated coastal reg ...
's
Imperial Valley The Imperial Valley ( or ''Valle Imperial'') of Southern California lies in Imperial and Riverside counties, with an urban area centered on the city of El Centro. The Valley is bordered by the Colorado River to the east and, in part, the S ...
, showing the most recorded activity in the area since the 1970s. Sometimes a series of earthquakes occur in what has been called an ''earthquake storm'', where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to
aftershock In seismology, an aftershock is a smaller earthquake that follows a larger earthquake, in Epicenter, the same area of the Mainshock, main shock, caused as the displaced Crust (geology), crust adjusts to the effects of the main shock. Large earthq ...
s but on adjacent segments of fault, these storms occur over the course of years, with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the
North Anatolian Fault The North Anatolian Fault (NAF; ) is an active right-lateral strike-slip fault in northern Anatolia, and is the transform boundary between the Eurasian plate and the Anatolian sub-plate. The fault extends westward from a junction with the Ea ...
in Turkey in the 20th century and has been inferred for older anomalous clusters of large earthquakes in the Middle East.


Frequency

It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt. Minor earthquakes occur very frequently around the world in places like California and Alaska in the U.S., as well as in El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia, the Philippines, Iran, Pakistan, the
Azores The Azores ( , , ; , ), officially the Autonomous Region of the Azores (), is one of the two autonomous regions of Portugal (along with Madeira). It is an archipelago composed of nine volcanic islands in the Macaronesia region of the North Atl ...
in Portugal, Turkey, New Zealand, Greece, Italy, India, Nepal, and Japan. Larger earthquakes occur less frequently, the relationship being
exponential Exponential may refer to any of several mathematical topics related to exponentiation, including: * Exponential function, also: **Matrix exponential, the matrix analogue to the above *Exponential decay, decrease at a rate proportional to value * Ex ...
; for example, roughly ten times as many earthquakes larger than magnitude 4 occur than earthquakes larger than magnitude 5. In the (low seismicity) United Kingdom, for example, it has been calculated that the average recurrences are: an earthquake of 3.7–4.6 every year, an earthquake of 4.7–5.5 every 10 years, and an earthquake of 5.6 or larger every 100 years. This is an example of the
Gutenberg–Richter law In seismology, the Gutenberg–Richter law (GR law) expresses the relationship between the Richter magnitude scale, magnitude and total number of earthquakes in any given region and time period of ''at least'' that magnitude. : \log_ N = a - b M ...
. The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, many more earthquakes are reported than in the past, but this is because of the vast improvement in instrumentation, rather than an increase in the number of earthquakes. The
United States Geological Survey The United States Geological Survey (USGS), founded as the Geological Survey, is an agency of the U.S. Department of the Interior whose work spans the disciplines of biology, geography, geology, and hydrology. The agency was founded on Mar ...
(USGS) estimates that, since 1900, there have been an average of 18 major earthquakes (magnitude 7.0–7.9) and one great earthquake (magnitude 8.0 or greater) per year, and that this average has been relatively stable. In recent years, the number of major earthquakes per year has decreased, though this is probably a statistical fluctuation rather than a systematic trend. More detailed statistics on the size and frequency of earthquakes is available from the United States Geological Survey. A recent increase in the number of major earthquakes has been noted, which could be explained by a cyclical pattern of periods of intense tectonic activity, interspersed with longer periods of low intensity. However, accurate recordings of earthquakes only began in the early 1900s, so it is too early to categorically state that this is the case. Most of the world's earthquakes (90%, and 81% of the largest) take place in the , horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific
Ring of Fire The Ring of Fire (also known as the Pacific Ring of Fire, the Rim of Fire, the Girdle of Fire or the Circum-Pacific belt) is a tectonic belt of volcanoes and earthquakes. It is about long and up to about wide, and surrounds most of the Pa ...
, which for the most part bounds the Pacific plate. Massive earthquakes tend to occur along other plate boundaries too, such as along the
Himalayan Mountains The Himalayas, or Himalaya ( ), is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has some of the Earth's highest peaks, including the highest, Mount Everest. More than 100 peak ...
. With the rapid growth of mega-cities such as Mexico City, Tokyo, and Tehran in areas of high
seismic risk Seismic risk or earthquake risk is the potential impact on the built environment and on people's well-being due to future earthquakes. Seismic risk has been defined, for most management purposes, as the potential economic, social and environment ...
, some seismologists are warning that a single earthquake may claim the lives of up to three million people.


Induced seismicity

While most earthquakes are caused by the movement of the Earth's
tectonic plate Plate tectonics (, ) is the scientific theory that the Earth's lithosphere comprises a number of large tectonic plates, which have been slowly moving since 3–4 billion years ago. The model builds on the concept of , an idea developed durin ...
s, human activity can also produce earthquakes. Activities both above ground and below may change the stresses and strains on the crust, including building reservoirs, extracting resources such as coal or oil, and injecting fluids underground for waste disposal or
fracking Fracking (also known as hydraulic fracturing, fracing, hydrofracturing, or hydrofracking) is a well stimulation technique involving the fracturing of formations in bedrock by a pressurized liquid. The process involves the high-pressure inje ...
. Most of these earthquakes have small magnitudes. The 5.7 magnitude
2011 Oklahoma earthquake The 2011 Oklahoma earthquake was a 5.7 Moment magnitude scale, magnitude intraplate earthquake which occurred near Prague, Oklahoma on November 5 at 10:53 p.m. CDT (03:53 UTC November 6) in the U.S. state of Oklahoma. ...
is thought to have been caused by disposing wastewater from oil production into
injection wells An injection well is a device that places fluid deep underground into porous rock formations, such as sandstone or limestone, or into or below the shallow soil layer. The fluid may be water, wastewater, brine (salt water), or water mixed with ind ...
, and studies point to the state's oil industry as the cause of other earthquakes in the past century. A
Columbia University Columbia University in the City of New York, commonly referred to as Columbia University, is a Private university, private Ivy League research university in New York City. Established in 1754 as King's College on the grounds of Trinity Churc ...
paper suggested that the 8.0 magnitude
2008 Sichuan earthquake An earthquake occurred in the province of Sichuan, China at 14:28:01 China Standard Time on May 12, 2008. Measuring at 8.0 (7.9–8.3 ), the earthquake's epicenter was located boxing the compass, west-northwest of Chengdu, the provincial ...
was induced by loading from the
Zipingpu Dam Zipingpu Dam (紫坪铺水利枢纽) is an embankment dam on the Min River near the city of Dujiangyan, Sichuan Province in southwest China. It consists of four generators with a total generating capacity of 760 MW. Construction began in 2001 ...
, though the link has not been conclusively proved.


Measurement and location

The instrumental scales used to describe the size of an earthquake began with the
Richter scale The Richter scale (), also called the Richter magnitude scale, Richter's magnitude scale, and the Gutenberg–Richter scale, is a measure of the strength of earthquakes, developed by Charles Richter in collaboration with Beno Gutenberg, and pr ...
in the 1930s. It is a relatively simple measurement of an event's amplitude, and its use has become minimal in the 21st century.
Seismic waves A seismic wave is a mechanical wave of acoustic wave, acoustic energy that travels through the Earth or another planetary body. It can result from an earthquake (or generally, a quake (natural phenomenon), quake), types of volcanic eruptions ...
travel through the
Earth's interior The internal structure of Earth are the layers of the Earth, excluding its atmosphere and hydrosphere. The structure consists of an outer silicate solid crust, a highly viscous asthenosphere, and solid mantle, a liquid outer core whose flow ge ...
and can be recorded by
seismometer A seismometer is an instrument that responds to ground displacement and shaking such as caused by quakes, volcanic eruptions, and explosions. They are usually combined with a timing device and a recording device to form a seismograph. The out ...
s at great distances. The
surface-wave magnitude The surface wave magnitude (M_s) scale is one of the magnitude scales used in seismology to describe the size of an earthquake. It is based on measurements of Rayleigh surface waves that travel along the uppermost layers of the Earth. This mag ...
was developed in the 1950s as a means to measure remote earthquakes and to improve the accuracy for larger events. The
moment magnitude scale The moment magnitude scale (MMS; denoted explicitly with or Mwg, and generally implied with use of a single M for magnitude) is a measure of an earthquake's magnitude ("size" or strength) based on its seismic moment. was defined in a 1979 paper ...
not only measures the amplitude of the shock but also takes into account the
seismic moment Seismic moment is a quantity used by seismologists to measure the size of an earthquake. The scalar seismic moment M_0 is defined by the equation M_0=\mu AD, where *\mu is the shear modulus of the rocks involved in the earthquake (in pascal (unit) ...
(total rupture area, average slip of the fault, and rigidity of the rock). The
Japan Meteorological Agency seismic intensity scale The Japan Meteorological Agency (JMA) Seismic Intensity Scale (known in Japan as the Shindo seismic scale) is a seismic intensity scale used in Japan to categorize the intensity of local ground shaking caused by earthquakes. The JMA intensit ...
, the
Medvedev–Sponheuer–Karnik scale The Medvedev–Sponheuer–Karnik scale, also known as the MSK or MSK-64, is a macroseismic intensity scale used to evaluate the severity of ground shaking on the basis of observed effects in an area where an earthquake transpires. The scale was f ...
, and the
Mercalli intensity scale The Modified Mercalli intensity scale (MM, MMI, or MCS) measures the effects of an earthquake at a given location. This is in contrast with the seismic magnitude usually reported for an earthquake. Magnitude scales measure the inherent force or ...
are based on the observed effects and are related to the intensity of shaking.


Intensity and magnitude

The shaking of the earth is a common phenomenon that has been experienced by humans from the earliest of times. Before the development of strong-motion accelerometers, the intensity of a seismic event was estimated based on the observed effects. Magnitude and intensity are not directly related and calculated using different methods. The magnitude of an earthquake is a single value that describes the size of the earthquake at its source. Intensity is the measure of shaking at different locations around the earthquake. Intensity values vary from place to place, depending on the distance from the earthquake and the underlying rock or soil makeup. The first scale for measuring earthquake magnitudes was developed by
Charles Francis Richter Charles Francis Richter (; April 26, 1900September 30, 1985) was an American seismologist and physicist. He is the namesake and one of the creators of the Richter scale, which, until the development of the moment magnitude scale in 1979, was w ...
in 1935. Subsequent scales (
seismic magnitude scales Seismic magnitude scales are used to describe the overall strength or "size" of an earthquake. These are distinguished from seismic intensity scales that categorize the intensity or severity of ground shaking (quaking) caused by an earthquake at ...
) have retained a key feature, where each unit represents a ten-fold difference in the amplitude of the ground shaking and a 32-fold difference in energy. Subsequent scales are also adjusted to have approximately the same numeric value within the limits of the scale. Although the mass media commonly reports earthquake magnitudes as "Richter magnitude" or "Richter scale", standard practice by most seismological authorities is to express an earthquake's strength on the moment magnitude scale, which is based on the actual energy released by an earthquake, the static seismic moment.


Seismic waves

Every earthquake produces different types of seismic waves, which travel through rock with different velocities: * Longitudinal P waves (shock- or pressure waves) * Transverse
S waves __NOTOC__ In seismology and other areas involving elastic waves, S waves, secondary waves, or shear waves (sometimes called elastic S waves) are a type of elastic wave and are one of the two main types of elastic body waves, so named because t ...
(both body waves) *
Surface wave In physics, a surface wave is a mechanical wave that propagates along the Interface (chemistry), interface between differing media. A common example is gravity waves along the surface of liquids, such as ocean waves. Gravity waves can also occu ...
s – (
Rayleigh Rayleigh may refer to: Science *Rayleigh scattering *Rayleigh–Jeans law *Rayleigh waves *Rayleigh (unit), a unit of photon flux named after the 4th Baron Rayleigh *Rayl, rayl or Rayleigh, two units of specific acoustic impedance and characte ...
and
Love wave In elastodynamics, Love waves, named after Augustus Edward Hough Love, are horizontally polarized surface waves. The Love wave is a result of the interference of many shear waves ( S-waves) guided by an elastic layer, which is ''welded'' to a ...
s)


Speed of seismic waves

Propagation velocity The phase velocity of a wave is the rate at which the wave propagates in any medium. This is the velocity at which the phase of any one frequency component of the wave travels. For such a component, any given phase of the wave (for example, t ...
of the seismic waves through solid rock ranges from approx. up to , depending on the
density Density (volumetric mass density or specific mass) is the ratio of a substance's mass to its volume. The symbol most often used for density is ''ρ'' (the lower case Greek letter rho), although the Latin letter ''D'' (or ''d'') can also be u ...
and elasticity of the medium. In the Earth's interior, the shock- or P waves travel much faster than the S waves (approx. relation 1.7:1). The differences in travel time from the
epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...
to the observatory are a measure of the distance and can be used to image both sources of earthquakes and structures within the Earth. Also, the depth of the
hypocenter A hypocenter or hypocentre (), also called ground zero or surface zero, is the point on the Earth's surface directly below a nuclear explosion, meteor air burst, or other mid-air explosion. In seismology, the hypocenter of an earthquake is its ...
can be computed roughly. P wave speed * Upper crust soils and unconsolidated sediments: per second * Upper crust solid rock: per second * Lower crust: per second * Deep mantle: per second. S waves speed * Light sediments: per second * Earths crust: per second * Deep mantle: per second


Seismic wave arrival

As a consequence, the first waves of a distant earthquake arrive at an observatory via the Earth's mantle. On average, the kilometer distance to the earthquake is the number of seconds between the P- and S wave arrival times, multiplied by 8. Slight deviations are caused by inhomogeneities of subsurface structure. By such analysis of seismograms, the Earth's core was located in 1913 by
Beno Gutenberg Beno Gutenberg (; June 4, 1889 – January 25, 1960) was a German-American seismologist who made several important contributions to the science. He was a colleague and mentor of Charles Francis Richter at the California Institute of Technolo ...
. S waves and later arriving surface waves do most of the damage compared to P waves. P waves squeeze and expand the material in the same direction they are traveling, whereas S waves shake the ground up and down and back and forth.


Location and reporting

Earthquakes are not only categorized by their magnitude but also by the place where they occur. The world is divided into 754
Flinn–Engdahl regions The Flinn-Engdahl regions (or F-E regions) comprise a set of contiguous seismic zones which cover the Earth's surface. In seismology, they are the standard for localizing earthquakes. The scheme was proposed in 1965 by Edward A. Flinn and E. R. E ...
(F-E regions), which are based on political and geographical boundaries as well as seismic activity. More active zones are divided into smaller F-E regions whereas less active zones belong to larger F-E regions. Standard reporting of earthquakes includes its
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
, date and time of occurrence,
geographic coordinates A geographic coordinate system (GCS) is a spherical or geodetic coordinate system for measuring and communicating positions directly on Earth as latitude and longitude. It is the simplest, oldest, and most widely used type of the various ...
of its
epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...
, depth of the epicenter, geographical region, distances to population centers, location uncertainty, several parameters that are included in USGS earthquake reports (number of stations reporting, number of observations, etc.), and a unique event ID. Although relatively slow seismic waves have traditionally been used to detect earthquakes, scientists realized in 2016 that gravitational measurement could provide instantaneous detection of earthquakes, and confirmed this by analyzing gravitational records associated with the 2011 Tohoku-Oki ("Fukushima") earthquake.


Effects

The effects of earthquakes include, but are not limited to, the following:


Shaking and ground rupture

Shaking and ground rupture are the main effects created by earthquakes, principally resulting in more or less severe damage to buildings and other rigid structures. The severity of the local effects depends on the complex combination of the earthquake
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
, the distance from the
epicenter The epicenter (), epicentre, or epicentrum in seismology is the point on the Earth's surface directly above a hypocenter or focus, the point where an earthquake or an underground explosion originates. Determination The primary purpose of a ...
, and the local geological and geomorphological conditions, which may amplify or reduce
wave propagation In physics, mathematics, engineering, and related fields, a wave is a propagating dynamic disturbance (change from equilibrium) of one or more quantities. '' Periodic waves'' oscillate repeatedly about an equilibrium (resting) value at some f ...
. The ground-shaking is measured by
ground acceleration Peak ground acceleration (PGA) is equal to the maximum ground acceleration that occurred during earthquake shaking at a location. PGA is equal to the amplitude of the largest absolute acceleration recorded on an wikt:accelerogram, accelerogram at a ...
. Specific local geological, geomorphological, and geostructural features can induce high levels of shaking on the ground surface even from low-intensity earthquakes. This effect is called site or local amplification. It is principally due to the transfer of the
seismic Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...
motion from hard deep soils to soft superficial soils and the effects of seismic energy focalization owing to the typical geometrical setting of such deposits. Ground rupture is a visible breaking and displacement of the Earth's surface along the trace of the fault, which may be of the order of several meters in the case of major earthquakes. Ground rupture is a major risk for large engineering structures such as
dams A dam is a barrier that stops or restricts the flow of surface water or underground streams. Reservoirs created by dams not only suppress floods but also provide water for activities such as irrigation, human consumption, industrial use, ...
, bridges, and
nuclear power stations A nuclear power plant (NPP), also known as a nuclear power station (NPS), nuclear generating station (NGS) or atomic power station (APS) is a thermal power station in which the heat source is a nuclear reactor. As is typical of thermal power st ...
and requires careful mapping of existing faults to identify any that are likely to break the ground surface within the life of the structure.


Soil liquefaction

Soil liquefaction occurs when, because of the shaking, water-saturated
granular Granularity (also called graininess) is the degree to which a material or system is composed of distinction (philosophy), distinguishable pieces, granular material, "granules" or grain, "grains" (metaphorically). It can either refer to the exten ...
material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. For example, in the
1964 Alaska earthquake The 1964 Alaska earthquake, also known as the Great Alaska earthquake and Good Friday earthquake, occurred at 5:36 PM Alaska Standard Time, AKST on Good Friday, March 27, 1964.
, soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.


Human impacts

Physical damage from an earthquake will vary depending on the intensity of shaking in a given area and the type of population. Underserved and developing communities frequently experience more severe impacts (and longer lasting) from a seismic event compared to well-developed communities. Impacts may include: * Injuries and loss of life * Damage to critical infrastructure (short and long-term) ** Roads, bridges, and public transportation networks ** Water, power, sewer and gas interruption ** Communication systems * Loss of critical community services including hospitals, police, and fire * General
property damage Property damage (sometimes called damage to property) is the damage or destruction of real or tangible personal property, caused by negligence, willful destruction, or an act of nature. Destruction of property (sometimes called property de ...
* Collapse or destabilization (potentially leading to future collapse) of buildings With these impacts and others, the aftermath may bring disease, a lack of basic necessities, mental consequences such as panic attacks and depression to survivors, and higher insurance premiums. Recovery times will vary based on the level of damage and the socioeconomic status of the impacted community.


Landslides

China stood out in several categories in a study group of 162 earthquakes (from 1772 to 2021) that included landslide fatalities. Due to the
2008 Sichuan earthquake An earthquake occurred in the province of Sichuan, China at 14:28:01 China Standard Time on May 12, 2008. Measuring at 8.0 (7.9–8.3 ), the earthquake's epicenter was located boxing the compass, west-northwest of Chengdu, the provincial ...
, it had 42% of all landslide fatalities within the study (total event deaths were higher). They were followed by Peru (22%) from the
1970 Ancash earthquake The 1970 Ancash earthquake (also known as the Great Peruvian earthquake) occurred on 31 May off the coast of Peru in the Pacific Ocean at . Combined with 1970 Huascarán debris avalanche, a resultant landslide, it is the most catastrophic natura ...
, and Pakistan (21%) from the
2005 Kashmir earthquake An earthquake occurred at on 8 October 2005 in Azad Jammu and Kashmir, a territory under Pakistan. Its epicenter was 19 km northeast of the city of Muzaffarabad, and 90 km north north-east of Islamabad, the capital city of Pakistan, ...
. China was also on top with the highest area affected by landslides with more than 80,000 km2, followed by Canada with 66,000 km2 ( 1988 Saguenay and 1946 Vancouver Island). Strike-slip (61 events) was the dominant fault type listed, followed closely by thrust/reverse (57), and normal (33).


Fires

Earthquakes can cause fires by damaging
electrical power Electric power is the rate of transfer of electrical energy within a electric circuit, circuit. Its SI unit is the watt, the general unit of power (physics), power, defined as one joule per second. Standard prefixes apply to watts as with oth ...
or gas lines. In the event of water mains rupturing and a loss of pressure, it may also become difficult to stop the spread of a fire once it has started. For example, more deaths in the
1906 San Francisco earthquake At 05:12 AM Pacific Time Zone, Pacific Standard Time on Wednesday, April 18, 1906, the coast of Northern California was struck by a major earthquake with an estimated Moment magnitude scale, moment magnitude of 7.9 and a maximum Mercalli inte ...
were caused by fire than by the earthquake itself.


Tsunami

Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water—including when an earthquake occurs at sea. In the open ocean, the distance between wave crests can surpass , and the wave periods can vary from five minutes to one hour. Such tsunamis travel 600–800 kilometers per hour (373–497 miles per hour), depending on water depth. Large waves produced by an earthquake or a submarine landslide can overrun nearby coastal areas in a matter of minutes. Tsunamis can also travel thousands of kilometers across open ocean and wreak destruction on far shores hours after the earthquake that generated them. Ordinarily, subduction earthquakes under magnitude 7.5 do not cause tsunamis, although some instances of this have been recorded. Most destructive tsunamis are caused by earthquakes of magnitude 7.5 or more.


Floods

Floods may be secondary effects of earthquakes if dams are damaged. Earthquakes may cause landslips to dam rivers, which collapse and cause floods. The terrain below the
Sarez Lake Sarez Lake ( ) is a lake in Rushon District of Gorno-Badakhshan province, Tajikistan. Its length is about , its depth about a few hundred meters, its water surface elevation about above sea level, and volume of water over . The mountains around ...
in Tajikistan is in danger of catastrophic flooding if the
landslide dam A landslide dam or barrier lake is the natural damming of a river by some kind of landslide, such as a debris flow, rock avalanche or volcanic eruption. If the damming landslide is caused by an earthquake, it may also be called a quake lake. Some ...
formed by the earthquake, known as the
Usoi Dam The Usoi Dam is a natural landslide dam along the Murghab River (Tajikistan), Murghab River in Tajikistan. At high, it is the tallest dam in the world, either natural or man-made. The dam was created on 18 February 1911, when the 7.4-Surface wav ...
, were to fail during a future earthquake. Impact projections suggest the flood could affect roughly five million people.


Management


Prediction

Earthquake prediction Earthquake prediction is a branch of the science of geophysics, primarily seismology, concerned with the specification of the time, location, and magnitude of future earthquakes within stated limits, and particularly "the determination of par ...
is a branch of the science of
seismology Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...
concerned with the specification of the time, location, and
magnitude Magnitude may refer to: Mathematics *Euclidean vector, a quantity defined by both its magnitude and its direction *Magnitude (mathematics), the relative size of an object *Norm (mathematics), a term for the size or length of a vector *Order of ...
of future earthquakes within stated limits. Many methods have been developed for predicting the time and place in which earthquakes will occur. Despite considerable research efforts by
seismologist Seismology (; from Ancient Greek σεισμός (''seismós'') meaning "earthquake" and -λογία (''-logía'') meaning "study of") is the scientific study of earthquakes (or generally, quakes) and the generation and propagation of elastic ...
s, scientifically reproducible predictions cannot yet be made to a specific day or month.Earthquake Prediction
. Ruth Ludwin, U.S. Geological Survey.
Popular belief holds earthquakes are preceded by earthquake weather, in the early morning.


Forecasting

While
forecasting Forecasting is the process of making predictions based on past and present data. Later these can be compared with what actually happens. For example, a company might Estimation, estimate their revenue in the next year, then compare it against the ...
is usually considered to be a type of
prediction A prediction (Latin ''præ-'', "before," and ''dictum'', "something said") or forecast is a statement about a future event or about future data. Predictions are often, but not always, based upon experience or knowledge of forecasters. There ...
, earthquake forecasting is often differentiated from
earthquake prediction Earthquake prediction is a branch of the science of geophysics, primarily seismology, concerned with the specification of the time, location, and magnitude of future earthquakes within stated limits, and particularly "the determination of par ...
. Earthquake forecasting is concerned with the probabilistic assessment of general earthquake hazards, including the frequency and magnitude of damaging earthquakes in a given area over years or decades. For well-understood faults the probability that a segment may rupture during the next few decades can be estimated.
Earthquake warning system An earthquake early warning (EEW) system is a system of accelerometers, seismometers, communication, computers, and alarms that is devised for rapidly notifying adjoining regions of a substantial earthquake once one begins. This is not the same ...
s have been developed that can provide regional notification of an earthquake in progress, but before the ground surface has begun to move, potentially allowing people within the system's range to seek shelter before the earthquake's impact is felt.


Preparedness

The objective of earthquake engineering is to foresee the impact of earthquakes on buildings, bridges, tunnels, roadways, and other structures, and to design such structures to minimize the risk of damage. Existing structures can be modified by seismic retrofitting to improve their resistance to earthquakes.
Earthquake insurance Earthquake insurance is a form of property insurance that pays the policyholder in the event of an earthquake that causes damage to the property. Most ordinary homeowners insurance policies do not cover earthquake damage. Most earthquake insuran ...
can provide building owners with financial protection against losses resulting from earthquakes.
Emergency management Emergency management (also Disaster management) is a science and a system charged with creating the framework within which communities reduce vulnerability to hazards and cope with disasters. Emergency management, despite its name, does not actu ...
strategies can be employed by a government or organization to mitigate risks and prepare for consequences.
Artificial intelligence Artificial intelligence (AI) is the capability of computer, computational systems to perform tasks typically associated with human intelligence, such as learning, reasoning, problem-solving, perception, and decision-making. It is a field of re ...
may help to assess buildings and plan precautionary operations. The Igor
expert system In artificial intelligence (AI), an expert system is a computer system emulating the decision-making ability of a human expert. Expert systems are designed to solve complex problems by reasoning through bodies of knowledge, represented mainly as ...
is part of a mobile laboratory that supports the procedures leading to the seismic assessment of masonry buildings and the planning of retrofitting operations on them. It has been applied to assess buildings in
Lisbon Lisbon ( ; ) is the capital and largest city of Portugal, with an estimated population of 567,131, as of 2023, within its administrative limits and 3,028,000 within the Lisbon Metropolitan Area, metropolis, as of 2025. Lisbon is mainlan ...
,
Rhodes Rhodes (; ) is the largest of the Dodecanese islands of Greece and is their historical capital; it is the List of islands in the Mediterranean#By area, ninth largest island in the Mediterranean Sea. Administratively, the island forms a separ ...
, and
Naples Naples ( ; ; ) is the Regions of Italy, regional capital of Campania and the third-largest city of Italy, after Rome and Milan, with a population of 908,082 within the city's administrative limits as of 2025, while its Metropolitan City of N ...
. Individuals can also take preparedness steps like securing water heaters and heavy items that could injure someone, locating shutoffs for utilities, and being educated about what to do when the shaking starts. For areas near large bodies of water, earthquake preparedness encompasses the possibility of a tsunami caused by a large earthquake.


In culture

From the lifetime of the Greek philosopher
Anaxagoras Anaxagoras (; , ''Anaxagóras'', 'lord of the assembly'; ) was a Pre-Socratic Greek philosopher. Born in Clazomenae at a time when Asia Minor was under the control of the Persian Empire, Anaxagoras came to Athens. In later life he was charged ...
in the 5th century BCE to the 14th century CE, earthquakes were usually attributed to "air (vapors) in the cavities of the Earth."
Pliny the Elder Gaius Plinius Secundus (AD 23/24 79), known in English as Pliny the Elder ( ), was a Roman Empire, Roman author, Natural history, naturalist, and naval and army commander of the early Roman Empire, and a friend of the Roman emperor, emperor Vesp ...
called earthquakes "underground thunderstorms".
Thales Thales of Miletus ( ; ; ) was an Ancient Greek philosophy, Ancient Greek Pre-Socratic philosophy, pre-Socratic Philosophy, philosopher from Miletus in Ionia, Asia Minor. Thales was one of the Seven Sages of Greece, Seven Sages, founding figure ...
of Miletus (625–547 BCE) was the only documented person who believed that earthquakes were caused by tension between the earth and water. In
Norse mythology Norse, Nordic, or Scandinavian mythology, is the body of myths belonging to the North Germanic peoples, stemming from Old Norse religion and continuing after the Christianization of Scandinavia as the Nordic folklore of the modern period. The ...
, earthquakes were explained as the violent struggle of the god
Loki Loki is a Æsir, god in Norse mythology. He is the son of Fárbauti (a jötunn) and Laufey (mythology), Laufey (a goddess), and the brother of Helblindi and Býleistr. Loki is married to the goddess Sigyn and they have two sons, Narfi (son of Lo ...
being punished for the murder of
Baldr Baldr (Old Norse also Balder, Baldur) is a god in Germanic mythology. In Norse mythology, he is a son of the god Odin and the goddess Frigg, and has numerous brothers, such as Thor and Váli. In wider Germanic mythology, the god was known in ...
, god of beauty and light. In
Greek mythology Greek mythology is the body of myths originally told by the Ancient Greece, ancient Greeks, and a genre of ancient Greek folklore, today absorbed alongside Roman mythology into the broader designation of classical mythology. These stories conc ...
,
Poseidon Poseidon (; ) is one of the twelve Olympians in ancient Greek religion and mythology, presiding over the sea, storms, earthquakes and horses.Burkert 1985pp. 136–139 He was the protector of seafarers and the guardian of many Hellenic cit ...
was the cause and god of earthquakes. In
Japanese mythology Japanese mythology is a collection of traditional stories, folktales, and beliefs that emerged in the islands of the Japanese archipelago. Shinto traditions are the cornerstones of Japanese mythology. The history of thousands of years of contac ...
, Namazu (鯰) is a giant
catfish Catfish (or catfishes; order (biology), order Siluriformes or Nematognathi) are a diverse group of ray-finned fish. Catfish are common name, named for their prominent barbel (anatomy), barbels, which resemble a cat's whiskers, though not ...
who causes earthquakes. In
Taiwan Taiwan, officially the Republic of China (ROC), is a country in East Asia. The main geography of Taiwan, island of Taiwan, also known as ''Formosa'', lies between the East China Sea, East and South China Seas in the northwestern Pacific Ocea ...
ese folklore, the Tē-gû (地牛) is a giant earth buffalo who causes earthquakes. In the
New Testament The New Testament (NT) is the second division of the Christian biblical canon. It discusses the teachings and person of Jesus in Christianity, Jesus, as well as events relating to Christianity in the 1st century, first-century Christianit ...
,
Matthew's Gospel The Gospel of Matthew is the first book of the New Testament of the Bible and one of the three synoptic Gospels. It tells the story of who the author believes is Israel's messiah ( Christ), Jesus, his resurrection, and his mission to the ...
refers to earthquakes occurring both after the
death of Jesus The crucifixion of Jesus was the death of Jesus by being nailed to a cross.The instrument of crucifixion is taken to be an upright wooden beam to which was added a transverse wooden beam, thus forming a "cruciform" or T-shaped structure. ...
( Matthew 27:51, 54) and at his
resurrection Resurrection or anastasis is the concept of coming back to life after death. Reincarnation is a similar process hypothesized by other religions involving the same person or deity returning to another body. The disappearance of a body is anothe ...
( Matthew 28:2).Allison, D., ''56. Matthew'', in Barton, J. and Muddiman, J. (2001)
The Oxford Bible Commentary
p. 884
In modern popular culture, the portrayal of earthquakes is shaped by the memory of great cities laid waste, such as Kobe in 1995 or San Francisco in 1906. Fictional earthquakes tend to strike suddenly and without warning. For this reason, stories about earthquakes generally begin with the disaster and focus on its immediate aftermath, as in ''Short Walk to Daylight'' (1972), '' The Ragged Edge'' (1968) or '' Aftershock: Earthquake in New York'' (1999). A notable example is Heinrich von Kleist's classic novella, '' The Earthquake in Chile'', which describes the destruction of Santiago in 1647.
Haruki Murakami is a Japanese writer. His novels, essays, and short stories have been best-sellers in Japan and internationally, with his work translated into 50 languages and having sold millions of copies outside Japan. He has received numerous awards for hi ...
's short fiction collection '' After the Quake'' depicts the consequences of the Kobe earthquake of 1995. The most popular single earthquake in fiction is the hypothetical "Big One" expected of California's
San Andreas Fault The San Andreas Fault is a continental Fault (geology)#Strike-slip faults, right-lateral strike-slip transform fault that extends roughly through the U.S. state of California. It forms part of the tectonics, tectonic boundary between the Paci ...
someday, as depicted in the novels '' Richter 10'' (1996), '' Goodbye California'' (1977), ''
2012 2012 was designated as: *International Year of Cooperatives *International Year of Sustainable Energy for All Events January *January 4 – The Cicada 3301 internet hunt begins. * January 12 – Peaceful protests begin in the R ...
'' (2009), and '' San Andreas'' (2015), among other works.


Outside of Earth

Phenomena similar to earthquakes have been observed on other planets (e.g., ''
marsquake A marsquake is a Quake (natural phenomenon), quake which, much like an earthquake, is a shaking of the surface or interior of the planet Mars. Such quakes may occur with a shift in the planet's interior, such as the result of plate tectonics, from ...
s'' on Mars) and on the Moon (e.g., '' moonquakes'').


See also

* * * * * *
Lists of earthquakes Earthquakes are caused by movements within the Earth's crust and uppermost Earth's mantle, mantle. They range from weak events detectable only by seismometers, to sudden and violent events lasting many minutes which have caused some of the greate ...
* * *


References


Sources

* . * . * , NUREG/CR-1457. * Deborah R. Coen. ''The Earthquake Observers: Disaster Science From Lisbon to Richter'' (
University of Chicago Press The University of Chicago Press is the university press of the University of Chicago, a Private university, private research university in Chicago, Illinois. It is the largest and one of the oldest university presses in the United States. It pu ...
; 2012) 348 pages; explores both scientific and popular coverage * . * . * . * .


Further reading

* *


External links


Earthquake Hazards Program
of the U.S. Geological Survey

– IRIS Consortium {{Authority control Geological hazards Lithosphere Natural disasters Seismology