An earthquake (also known as a quake, tremor, temblor or seismic activity) is the result of a sudden release of energy in the Earth's Earth is the third planet from the Sun, and the densest and fifth-largest of the eight planets in the Solar System. It is also the largest of the Solar System's four terrestrial planets. It is sometimes referred to as the World, the Blue Planet,[note 6] or by its Latin name, Terra.[note 7] crust In geology, a crust is the outermost solid shell of a rocky planet or moon, which is chemically distinct from the underlying mantle. The crusts of Earth, our Moon, Mercury, Venus, Mars, Io, and other planetary bodies have been generated largely by igneous processes, and these crusts are richer in incompatible elements than their respective mantles that creates seismic waves Seismic waves are waves of force that travel through the Earth or other elastic bodies, for example as a result of an earthquake, explosion, or some other process that imparts forces. Seismic waves are studied by seismologists, and measured by a seismograph, which records the output of a seismometer, or geophone. For seismic studies of oil. Earthquakes are measured with a seismometer Seismometers are instruments that measure motions of the ground, including those of seismic waves generated by earthquakes, nuclear explosions, and other seismic sources. Records of seismic waves allow seismologists to map the interior of the Earth, and locate and measure the size of these different sources; a device which also records is known as a seismograph. The moment magnitude The moment magnitude scale is used by seismologists to measure the size of earthquakes in terms of the energy released. The magnitude is based on the moment of the earthquake, which is equal to the rigidity of the Earth multiplied by the average amount of slip on the fault and the size of the area that slipped. The scale was developed in the 1970s (or the related and mostly obsolete Richter The Richter magnitude scale, also known as the local magnitude scale, assigns a single number to quantify the amount of seismic energy released by an earthquake. It is a base-10 logarithmic scale obtained by calculating the logarithm of the combined horizontal amplitude (shaking amplitude) of the largest displacement from zero on a particular type magnitude) of an earthquake is conventionally reported, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale The Mercalli intensity scale is a scale used for measuring the intensity of an earthquake. The scale quantifies the effects of an earthquake on the Earth's surface, humans, objects of nature, and man-made structures on a scale of I through XII, with I denoting not felt, and XII total destruction. The values will differ based on the distance to the.

At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacing the ground. When a large earthquake epicenter The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates. The word derives from the Neolatin noun epicentrum from the Greek adjective ἐπίκεντρος "central", from ἐπί (epi) "on, upon, at" and κέ� is located offshore, the seabed sometimes suffers sufficient displacement to cause a tsunami A tsunami (Japanese: 津波 [tsɯnami], lit. 'harbor wave'; English pronunciation: /suːˈnɑːmi/ (t)soo-NAH-mee) or tidal wave is a series of water waves (called a tsunami wave train) caused by the displacement of a large volume of a body of water, usually an ocean, but can occur in large lakes. Tsunamis are a frequent occurrence in Japan;. The shaking in earthquakes can also trigger landslides and occasionally volcanic activity.

In its most generic sense, the word earthquake is used to describe any seismic event — whether a natural phenomenon A phenomenon , plural phenomena, is any observable occurrence. In popular usage, a phenomenon often refers to an extraordinary event. In scientific usage, a phenomenon is any event that is observable, however commonplace it might be, even if it requires the use of instrumentation to observe it. For example, in physics, a phenomenon may be a or an event caused by humans — that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults In geology, a fault is a planar fracture or discontinuity in a volume of rock, across which there has been significant displacement. Large faults within the Earth's crust result from the action of tectonic forces. Energy release associated with rapid movement on active faults is the cause of most earthquakes, but also by volcanic activity, landslides, mine blasts, and nuclear experiments. An earthquake's point of initial rupture is called its focus The hypocenter or hypocentre , refers to the site of an earthquake or a nuclear explosion. In the former, it is a synonym of the focus; in the latter, of ground zero or hypocenter The hypocenter or hypocentre , refers to the site of an earthquake or a nuclear explosion. In the former, it is a synonym of the focus; in the latter, of ground zero. The term epicenter The epicenter or epicentre is the point on the Earth's surface that is directly above the hypocenter or focus, the point where an earthquake or underground explosion originates. The word derives from the Neolatin noun epicentrum from the Greek adjective ἐπίκεντρος "central", from ἐπί (epi) "on, upon, at" and κέ� refers to the point at ground level directly above the hypocenter.

Naturally occurring earthquakes

Tectonic earthquakes will occur anywhere within the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. In the case of transform A transform fault or transform boundary, also known as conservative plate boundary, is a fault which runs along the boundary of a tectonic plate. The relative motion of such plates is horizontal in either sinistral or dextral direction. Typically, some vertical motion may also exist, but the principal vectors in a transform fault are oriented or convergent In plate tectonics, a convergent boundary also known as a destructive plate boundary , is an actively deforming region where two (or more) tectonic plates or fragments of lithosphere move toward one another and collide. As a result of pressure, friction, and plate material melting in the mantle, earthquakes and volcanoes are common near convergent type plate boundaries, which form the largest fault surfaces on earth, they will move past each other smoothly and aseismically In geology, aseismic creep is measurable surface displacement along a fault in the absence of notable earthquakes only if there are no irregularities or asperities Asperity, defined as "unevenness of surface, roughness, ruggedness" , has implications (for example) in physics and in seismology. Smooth surfaces, even those polished to a mirror finish, are not truly smooth on an atomic scale. They are rough, with sharp, rough or rugged projections, termed "asperities" along the boundary that increase the frictional resistance. Most boundaries do have such asperities and this leads to a form of stick-slip behaviour Stick-slip is caused by the surfaces alternating between sticking to each other and sliding over each other, with a corresponding change in the force of friction. Typically, the static friction coefficient between two surfaces is larger than the kinetic friction coefficient. If an applied force is large enough to overcome the static friction, then. Once the boundary 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 In physics, Potential energy is energy stored within a physical system as a result of the position or configuration of the different parts of that system. It has the potential to be converted into other forms of energy, such as kinetic energy, and to do work in the process. The SI unit of measure for energy and work is the joule (symbol J). This energy is released as a combination of radiated elastic strain In continuum mechanics, deformation or strain is the change in the metric properties of a continuous body B in the displacement from an initial placement κ0 to a final placement κ(B). A change in the metric properties means that a curve drawn in the initial body placement changes its length when displaced to a curve in the final placement. If seismic waves Seismic waves are waves of force that travel through the Earth or other elastic bodies, for example as a result of an earthquake, explosion, or some other process that imparts forces. Seismic waves are studied by seismologists, and measured by a seismograph, which records the output of a seismometer, or geophone. For seismic studies of oil, 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. 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 A fracture is any local separation or discontinuity plane in a geologic formation, such as a joint or a fault that divides the rock into two or more pieces. Fractures are commonly caused by stress exceeding the rock strength. Fractures can provide permeability for fluid movement, such as water or hydrocarbons. Highly fractured rocks can make good growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy Elastic energy is the energy which causes or is released by the elastic distortion of a solid or liquid 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.^[1]

Earthquake fault types

There are three main types of fault that may cause an earthquake: 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 Strike and dip refer to the orientation or attitude of a geologic feature. The strike of a bed, fault, or other planar feature is a line representing the intersection of that feature with a horizontal plane. On a geologic map this is represented with a short straight line segment oriented parallel to the compass direction of the strike. Strike can and movement on them involves a vertical component. Normal faults occur mainly in areas where the crust is being extended Extensional tectonics is concerned with the structures formed, and the tectonic processes associated with, the stretching of the crust or lithosphere such as a divergent boundary In plate tectonics, a divergent boundary or divergent plate boundary is a linear feature that exists between two tectonic plates that are moving away from each other. These areas can form on the end of continents but eventually form ocean basins. Divergent boundaries within continents initially produce rifts which produce rift valleys. Therefore,. Reverse faults occur in areas where the crust is being shortened Thrust tectonics or contractional tectonics is concerned with the structures formed, and the tectonic processes associated with, the shortening and thickening of the crust or lithosphere such as at a convergent boundary. Strike-slip faults 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. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip.

Earthquakes away from plate boundaries

Where plate boundaries occur within continental lithosphere The continental crust is the layer of igneous, sedimentary, and metamorphic rocks which form the continents and the areas of shallow seabed close to their shores, known as continental shelves. This layer is sometimes called sial due to more felsic, or granitic, bulk composition, which lies in contrast to the oceanic crust, called sima due to its, deformation is spread out over a much larger area than the plate boundary itself. In the case of the San Andreas fault The San Andreas Fault is a continental transform fault that runs a length of roughly 810 miles through California in the United States. The fault's motion is right-lateral strike-slip (horizontal motion). It forms the tectonic boundary between the Pacific Plate and the North American Plate continental transform, many earthquakes occur away from the plate boundary and are related to strains developed within the broader zone of deformation caused by major irregularities in the fault trace (e.g. the “Big bend” region). The Northridge earthquake The Northridge earthquake occurred on January 17, 1994 at 4:31 AM Pacific Standard Time in Northridge, a neighborhood in the city of Los Angeles, California, lasting for about 45 seconds. The earthquake had a "strong" moment magnitude of 6.7, but the ground acceleration was one of the highest ever instrumentally recorded in an urban area was associated with movement on a blind thrust within such a zone. Another example is the strongly oblique convergent plate boundary between the Arabian The Arabian Plate is one of three tectonic plates which have been moving northward over millions of years and colliding with the Eurasian Plate. This is resulting in a mingling of plate pieces and mountain ranges extending in the west from the Pyrenees, crossing southern Europe and the Middle East, to the Himalayas and ranges of southeast Asia and Eurasian plates The Eurasian Plate is a tectonic plate which includes most of the continent of Eurasia , with the notable exceptions of the Indian subcontinent, the Arabian subcontinent, and the area east of the Chersky Range in East Siberia. It also includes oceanic crust extending westward to the Mid-Atlantic Ridge and northward to the Gakkel Ridge where it runs through the northwestern part of the Zagros The Zagros Mountains are the largest mountain range in Iran and Iraq. With a total length of 1,500 km (932 mi), from northwestern Iran, and roughly correlating with Iran's western border, the Zagros range spans the whole length of the western and southwestern Iranian plateau and ends at the Straits of Hormuz. The highest points in the Zagros mountains. The deformation associated with this plate boundary is partitioned into nearly pure thrust sense movements perpendicular to the boundary over a wide zone to the southwest and nearly pure strike-slip motion along the Main Recent Fault close to the actual plate boundary itself. This is demonstrated by earthquake focal mechanisms.^[2]

All tectonic plates have internal stress fields caused by their interactions with neighbouring plates and sedimentary loading or unloading (e.g. deglaciation). These stresses may be sufficient to cause failure along existing fault planes, giving rise to intraplate earthquakes An intraplate earthquake is an earthquake that occurs in the interior of a tectonic plate, whereas an interplate earthquake is one that occurs at a plate boundary.^[3]

Shallow-focus and deep-focus earthquakes

The majority of tectonic earthquakes originate at the ring of fire in depths not exceeding tens of kilometers. Earthquakes occurring at a depth of less than 70 km are classified as 'shallow-focus' earthquakes, while those with a focal-depth between 70 and 300 km are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes. In subduction zones In geology, subduction is the process that takes place at convergent boundaries by which one tectonic plate moves under another tectonic plate, sinking into the Earth's mantle, as the plates converge. A subduction zone is an area on Earth where two tectonic plates move towards one another and subduction occurs. Rates of subduction are typically, where older and colder oceanic crust Oceanic crust is the part of Earth's lithosphere that surfaces in the ocean basins. Oceanic crust is primarily composed of mafic rocks, or sima, which is rich in iron and magnesium. It is thinner than continental crust, or sial, generally less than 10 kilometers thick, however it is denser, having a mean density of about 3.3 grams per cubic descends beneath another tectonic plate, deep-focus earthquakes may occur at much greater depths (ranging from 300 up to 700 kilometers).^[4] These seismically active areas of subduction are known as Wadati-Benioff zones A Wadati-Benioff zone is a deep active seismic area in a subduction zone. Differential motion along the zone produces deep-seated earthquakes, the foci of which may be as deep as about 700 kilometres (435 miles). They develop beneath volcanic island arcs and continental margins above active subduction zones. They can be produced by slip along the. Deep-focus earthquakes occur at a depth at which the subducted lithosphere The lithosphere is the rigid outermost shell of a rocky planet. It comprises the crust and the portion of the upper mantle that behaves elastically on time scales of thousands of years or greater 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 with the formula (Mg,Fe)2Si undergoing a phase transition A phase transition is the transformation of a thermodynamic system from one phase or state of matter to another into a spinel Spinel is the magnesium aluminium member of the larger spinel group of minerals. It has the formula MgAl2O4. Balas ruby is an old name for a rose-tinted variety structure.^[5]

Earthquakes and volcanic activity

Earthquakes often occur in volcanic regions and are caused there, both by tectonic Plate tectonics is a scientific theory which describes the large scale motions of Earth's lithosphere. It is vital for the existence of life on earth because of the role that it plays in the global cycle that maintains the balance of carbon between the biosphere, pedosphere, geosphere, hydrosphere, and atmosphere.[citation needed] The theory faults and the movement of magma Magma [from Greek μάγμα, paste] is a mixture of molten rock, volatiles and solids that is found beneath the surface of the Earth, and may also exist on other terrestrial planets. Besides molten rock, magma may also contain suspended crystals and gas bubbles. Magma often collects in magma chambers that may feed a volcano or turn into a pluton in volcanoes A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, ash and gases to escape from below the surface. Such earthquakes can serve as an early warning of volcanic eruptions, as during the Mount St. Helens Mount St. Helens is an active stratovolcano located in Skamania County, Washington, in the Pacific Northwest region of the United States. It is 96 miles south of Seattle and 50 miles (80 km) northeast of Portland, Oregon. Mount St. Helens takes its English name from the British diplomat Lord St Helens, a friend of explorer George Vancouver who eruption of 1980 The 1980 eruption of Mount St. Helens, a stratovolcano located in Washington state, in the United States, was a major volcanic eruption. The eruption was the only significant one to occur in the contiguous 48 U.S. states since the 1915 eruption of Lassen Peak in California.^[6] 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 (a device which measures the ground slope) and used as sensors to predict imminent or upcoming eruptions.^[7]

Rupture dynamics

A tectonic earthquake begins by an initial rupture at a point on the fault surface, a process known as nucleation. The scale of the nucleation zone is uncertain, with some evidence, such as the rupture dimensions of the smallest earthquakes, suggesting that it is smaller than 100 m while other evidence, such as a slow component revealed by low-frequency spectra of some earthquakes, suggest that it is larger. The possibility that the nucleation involves some sort of preparation process is supported by the observation that about 40% of earthquakes are preceded by foreshocks. Once the rupture has initiated it begins to propagate along the fault surface. The mechanics of this process are poorly understood, partly because it is difficult to recreate the high sliding velocities in a laboratory. Also the effects of strong ground motion make it very difficult to record information close to a nucleation zone.^[8]

Rupture propagation is generally modelled using a fracture mechanics Fracture mechanics is the field of mechanics concerned with the study of the formation of cracks in materials. It uses methods of analytical solid mechanics to calculate the driving force on a crack and those of experimental solid mechanics to characterize the material's resistance to fracture approach, likening the rupture to a propagating mixed mode shear crack. The rupture velocity is a function of the fracture energy in the volume around the crack tip, increasing with decreasing fracture energy. The velocity of rupture propagation is orders of magnitude faster than the displacement velocity across the fault. Earthquake ruptures typically propagate at velocities that are in the range 70–90 % of the S-wave velocity and this is independent of earthquake size. A small subset of earthquake ruptures appear to have propagated at speeds greater than the S-wave velocity. These supershear earthquakes have all been observed during large strike-slip events. The unusually wide zone of coseismic damage caused by the 2001 Kunlun earthquake has been attributed to the effects of the sonic boom developed in such earthquakes. Some earthquake ruptures travel at unusually low velocities and are referred to as slow earthquakes. A particularly dangerous form of slow earthquake is the tsunami earthquake, observed where the relatively low felt intensities, caused by the slow propagation speed of some great earthquakes, fail to alert the population of the neighbouring coast, as in the 1896 Meiji-Sanriku earthquake.^[8]

Earthquake clusters

Most earthquakes form part of a sequence, related to each other in terms of location and time.^[9] Most earthquake clusters consist of small tremors which cause little to no damage, but there is a theory that earthquakes can recur in a regular pattern.^[10]

Aftershocks

An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. An aftershock is in the same region of the main shock but always of a smaller magnitude. If an aftershock is larger than the main shock, the aftershock is redesignated as the main shock and the original main shock is redesignated as a foreshock. Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the main shock.^[9]

Earthquake swarms

Earthquake swarms are sequences of earthquakes striking in a specific area within a short period of time. They are different from earthquakes followed by a series of aftershocks by the fact that no single earthquake in the sequence is obviously the main shock, therefore none have notable higher magnitudes than the other. An example of an earthquake swarm is the 2004 activity at Yellowstone National Park.^[11]

Earthquake storms

Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but on adjacent segments of fault, these storms occur over the course of years, and 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 in Turkey in the 20th century and has been inferred for older anomalous clusters of large earthquakes in the Middle East.^[12][13]

Size and frequency of occurrence

There are around 500,000 earthquakes each year. 100,000 of these can actually be felt.^[14][15] Minor earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in Guatemala. Chile, Peru, Indonesia, Iran, Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, and Japan, but earthquakes can occur almost anywhere, including New York City, London, and Australia.^[16] Larger earthquakes occur less frequently, the relationship being exponential; for example, roughly ten times as many earthquakes larger than magnitude 4 occur in a particular time period 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.^[17] This is an example of the Gutenberg-Richter law.

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 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.^[19] In recent years, the number of major earthquakes per year has decreased, although this is thought likely to be a statistical fluctuation rather than a systematic trend. More detailed statistics on the size and frequency of earthquakes is available from the USGS.^[20]

Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-km-long, horseshoe-shaped zone called the circum-Pacific seismic belt, known as the Pacific Ring of Fire, which for the most part bounds the Pacific Plate.^[21][22] Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains.

With the rapid growth of mega-cities such as Mexico City, Tokyo and Tehran, in areas of high seismic risk, some seismologists are warning that a single quake may claim the lives of up to 3 million people.^[23]

Induced seismicity

While most earthquakes are caused by movement of the Earth's tectonic plates, human activity can also produce earthquakes. Four main activities contribute to this phenomenon: constructing large dams and buildings, drilling and injecting liquid into wells, and by coal mining and oil drilling.^[24] Perhaps the best known example is the 2008 Sichuan earthquake in China's Sichuan Province in May; this tremor resulted in 69,227 fatalities and is the 19th deadliest earthquake of all time. The Zipingpu Dam is believed to have fluctuated the pressure of the fault 1,650 feet (503 m) away; this pressure probably increased the power of the earthquake and accelerated the rate of movement for the fault.^[25] The greatest earthquake in Australia's history was also induced by humanity, through coal mining. The city of Newcastle was built over a large sector of coal mining areas. The earthquake was spawned from a fault which reactivated due to the millions of tonnes of rock removed in the mining process.^[26]

Measuring and locating earthquakes

Earthquakes can be recorded by seismometers up to great distances, because seismic waves travel through the whole Earth's interior. The absolute magnitude of a quake is conventionally reported by numbers on the Moment magnitude scale (formerly Richter scale, magnitude 7 causing serious damage over large areas), whereas the felt magnitude is reported using the modified Mercalli intensity scale (intensity II-XII).

Every tremor produces different types of seismic waves which travel through rock with different velocities: the longitudinal P-waves (shock- or pressure waves), the transverse S-waves (both body waves) and several surface waves (Rayleigh and Love waves). The propagation velocity of the seismic waves ranges from approx. 3 km/s up to 13 km/s, depending on the density 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 epicentre to the observatory are a measure of the distance and can be used to image both sources of quakes and structures within the Earth. Also the depth of the hypocenter can be computed roughly.

In solid rock P-waves travel at about 6 to 7 km per second; the velocity increases within the deep mantle to ~13 km/s. The velocity of S-waves ranges from 2–3 km/s in light sediments and 4–5 km/s in the Earth's crust up to 7 km/s in the deep mantle. As a consequence, the first waves of a distant earth quake arrive at an observatory via the Earth's mantle.

Rule of thumb: On the average, the kilometer distance to the earthquake is the number of seconds between the P and S wave times 8 [1]. Slight deviations are caused by inhomogenities of subsurface structure. By such analyses of seismograms the Earth's core was located in 1913 by Beno Gutenberg.

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 (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.

Effects/impacts of earthquakes

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, the distance from the epicenter, and the local geological and geomorphological conditions, which may amplify or reduce wave propagation.^[27] The ground-shaking is measured by ground acceleration.

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 motion from hard deep soils to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical setting of the 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 metres in the case of major earthquakes. Ground rupture is a major risk for large engineering structures such as dams, bridges and nuclear power stations and requires careful mapping of existing faults to identify any likely to break the ground surface within the life of the structure.^[28]

Landslides and avalanches

Earthquakes, along with severe storms, volcanic activity, coastal wave attack, and wildfires, can produce slope instability leading to landslides, a major geological hazard. Landslide danger may persist while emergency personnel are attempting rescue.^[29]

Fires

Earthquakes can cause fires by damaging electrical power 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 were caused by fire than by the earthquake itself.^[30]

Soil liquefaction

Soil liquefaction occurs when, because of the shaking, water-saturated granular 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. This can be a devastating effect of earthquakes. For example, in the 1964 Alaska earthquake, soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.^[31]

Tsunami

Tsunamis are long-wavelength, long-period sea waves produced by the sudden or abrupt movement of large volumes of water. In the open ocean the distance between wave crests can surpass 100 kilometers (62 miles), 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.^[32]

Ordinarily, subduction earthquakes under magnitude 7.5 on the Richter scale 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.^[32]

Floods

A flood is an overflow of any amount of water that reaches land.^[33] Floods occur usually when the volume of water within a body of water, such as a river or lake, exceeds the total capacity of the formation, and as a result some of the water flows or sits outside of the normal perimeter of the body. However, floods may be secondary effects of earthquakes, if dams are damaged. Earthquakes may cause landslips to dam rivers, which then collapse and cause floods.^[34]

The terrain below the Sarez Lake in Tajikistan is in danger of catastrophic flood if the landslide dam formed by the earthquake, known as the Usoi Dam, were to fail during a future earthquake. Impact projections suggest the flood could affect roughly 5 million people.^[35]

Tidal forces

Research work has shown a robust correlation between small tidally induced forces and non-volcanic tremor activity.^{[36][37][38][39]}

Human impacts

Earthquakes may lead to disease, lack of basic necessities, loss of life, higher insurance premiums, general property damage, road and bridge damage, and collapse or destabilization (potentially leading to future collapse) of buildings. Earthquakes can also precede volcanic eruptions, which cause further problems; for example, substantial crop damage, as in the "Year Without a Summer" (1816).^[40]

Major earthquakes

The largest earthquake that has been measured was the 9.5 magnitude one in Chile in 1960.^[14][15]

Preparation

In order to determine the likelihood of future seismic activity, geologists and other scientists examine the rock of an area to determine if the rock appears to be "strained". Studying the faults of an area to study the buildup time it takes for the fault to build up stress sufficient for an earthquake also serves as an effective prediction technique.^[41] Measurements of the amount of accumulated strain energy on the fault each year, time passed since the last major temblor, and the energy and power of the last earthquake are made.^[41] Together the facts allow scientists to determine how much pressure it takes for the fault to generate an earthquake. Though this method is useful, it has only been implemented on California's San Andreas Fault.^[41]

Today, there are ways to protect and prepare possible sites of earthquakes from severe damage, through the following processes: earthquake engineering, earthquake preparedness, household seismic safety, seismic retrofit (including special fasteners, materials, and techniques), seismic hazard, mitigation of seismic motion, and earthquake prediction. Seismic retrofitting is the modification of existing structures to make them more resistant to seismic activity, ground motion, or soil failure due to earthquakes. With better understanding of seismic demand on structures and with our recent experiences with large earthquakes near urban centers, the need of seismic retrofitting is well acknowledged. Prior to the introduction of modern seismic codes in the late 1960s for developed countries (US, Japan etc.) and late 1970s for many other parts of the world (Turkey, China etc.),^[42], many structures were designed without adequate detailing and reinforcement for seismic protection. In view of the imminent problem, various research work has been carried out. Furthermore, state-of-the-art technical guidelines for seismic assessment, retrofit and rehabilitation have been published around the world - such as the ASCE-SEI 41 ^[43] and the New Zealand Society for Earthquake Engineering (NZSEE)'s guidelines ^[44].

History

Pre-Middle Ages

From the lifetime of the Greek philosopher Anaxagoras in the 5th century BCE to the 14th century CE, earthquakes were usually attributed to "air (vapors) in the cavities of the Earth".^[45] Thales of Miletus, who lived from 625-547 (BCE) was the only documented person who believed that earthquakes were caused by tension between the earth and water.^[45] Other theories existed, including the Greek philosopher Anaxamines' (585-526 BCE) beliefs that short incline episodes of dryness and wetness caused seismic activity. The Greek philosopher Democritus (460-371BCE) blamed water in general for earthquakes.^[45] Pliny the Elder called earthquakes "underground thunderstorms".^[45]

Earthquakes in culture

Mythology and religion

In Norse mythology, earthquakes were explained as the violent struggling of the god Loki. When Loki, god of mischief and strife, murdered Baldr, god of beauty and light, he was punished by being bound in a cave with a poisonous serpent placed above his head dripping venom. Loki's wife Sigyn stood by him with a bowl to catch the poison, but whenever she had to empty the bowl the poison would drip on Loki's face, forcing him to jerk his head away and thrash against his bonds, causing the earth to tremble.^[46]

In Greek mythology, Poseidon was the cause and god of earthquakes. When he was in a bad mood, he would strike the ground with a trident, causing this and other calamities. He also used earthquakes to punish and inflict fear upon people as revenge.^[47]

In Japanese mythology, Namazu (鯰) is a giant catfish who causes earthquakes. Namazu lives in the mud beneath the earth, and is guarded by the god Kashima who restrains the fish with a stone. When Kashima lets his guard fall, Namazu thrashes about, causing violent earthquakes.

Popular culture

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.^[48] Fictional earthquakes tend to strike suddenly and without warning.^[48] 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 (1998).^[48] A notable example is Heinrich von Kleist's classic novella, The Earthquake in Chile, which describes the destruction of Santiago in 1647. Haruki Murakami'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 someday, as depicted in the novels Richter 10 (1996) and Goodbye California (1977) among other works.^[48] Jacob M. Appel's widely anthologized short story, A Comparative Seismology, features a con artist who convinces an elderly woman that an apocalyptic earthquake is imminent.^[49] In Pleasure Boating in Lituya Bay, one of the stories in Jim Shepard's Like You'd Understand, Anyway, the "Big One" leads to an even more devastating tsunami.

In the film 2012 (2009), solar flares (geologically implausibly) affecting the Earth's core caused massive destabilization of the Earth's crust layers. This created destruction planet-wide with earthquakes and tsunamis, foreseen by the Mayan culture and myth surrounding the last year noted in the Mesoamerican calendar - 2012.

Contemporary depictions of earthquakes in film are variable in the manner in which they reflect human psychological reactions to the actual trauma that can be caused to directly afflicted families and their loved ones.^[50] Disaster mental health response research emphasizes the need to be aware of the different roles of loss of family and key community members, loss of home and familiar surroundings, loss of essential supplies and services to maintain survival.^[51][52] Particularly for children, the clear availability of caregiving adults who are able to protect, nourish, and clothe them in the aftermath of the earthquake, and to help them make sense of what has befallen them has been shown to be even more important to their emotional and physical health than the simple giving of provisions.^[53] As was observed after other disasters involving destruction and loss of life and their media depictions, such as those of the 2001 World Trade Center Attacks or Hurricane Katrina—and has been recently observed in the 2010 Haiti Earthquake, it is also important not to pathologize the reactions to loss and displacement or disruption of governmental administration and services, but rather to validate these reactions, to support constructive problem-solving and reflection as to how one might improve the conditions of those affected.^[54]

See also

• Disaster preparedness
• Earthquake engineering
• Earthquake insurance
• Earthquake loss
• Earthquake prediction
• Historical earthquakes
• Intraplate earthquake
• List of earthquakes
• List of all deadly earthquakes since 1900
• List of earthquakes by death toll
• Megathrust earthquake
• Moment magnitude scale
• Richter magnitude scale
• Seismite
• Seismology
• Seismotectonics
• Submarine earthquake
• Triangle of Life

Notes

1. ^ Spence, William; S. A. Sipkin, G. L. Choy (1989). "Measuring the Size of an Earthquake". United States Geological Survey. http://earthquake.usgs.gov/learning/topics/measure.php. Retrieved 2006-11-03.
2. ^ Talebian, M. Jackson, J. 2004. A reappraisal of earthquake focal mechanisms and active shortening in the Zagros mountains of Iran. Geophysical Journal International, 156, pages 506-526
3. ^ Noson, Qamar, and Thorsen (1988). Washington State Earthquake Hazards: Washington State Department of Natural Resources. Washington Division of Geology and Earth Resources Information Circular 85.
4. ^ "M7.5 Northern Peru Earthquake of 26 September 2005" (pdf). USGS. ftp://hazards.cr.usgs.gov/maps/sigeqs/20050926/20050926.pdf. Retrieved 2008-08-01.
5. ^ Greene, H. W.; Burnley, P. C. (October 26, 1989). "A new self-organizing mechanism for deep-focus earthquakes". Nature 341: 733–737. doi:10.1038/341733a0.
6. ^ Foxworthy and Hill (1982). Volcanic Eruptions of 1980 at Mount St. Helens, The First 100 Days: USGS Professional Paper 1249.
7. ^ Watson, John; Watson, Kathie (January 7, 1998). "Volcanoes and Earthquakes". United States Geological Survey. http://pubs.usgs.gov/gip/earthq1/volcano.html. Retrieved May 9, 2009.
8. ^ ^{a b} National Research Council (U.S.). Committee on the Science of Earthquakes (2003). "5. Earthquake Physics and Fault-System Science". Living on an Active Earth: Perspectives on Earthquake Science. Washington D.C.: National Academies Press. p. 418. ISBN 9780309065627. http://www.nap.edu/openbook.php?record_id=10493&page=282. Retrieved 8 July 2010.
9. ^ ^{a b} "What are Aftershocks, Foreshocks, and Earthquake Clusters?". http://earthquake.usgs.gov/eqcenter/step/explain.php.
10. ^ "Repeating Earthquakes". United States Geological Survey. January 29, 2009. http://earthquake.usgs.gov/research/parkfield/repeat.php. Retrieved May 11, 2009.
11. ^ "Earthquake Swarms at Yellowstone". USGS. http://volcanoes.usgs.gov/yvo/2004/Apr04Swarm.html. Retrieved 2008-09-15.
12. ^ Amos Nur (2000). "Poseidon’s Horses: Plate Tectonics and Earthquake Storms in the Late Bronze Age Aegean and Eastern Mediterranean". Journal of Archaeological Science 27: 43–63. doi:10.1006/jasc.1999.0431. ISSN 0305-4403. http://water.stanford.edu/nur/EndBronzeage.pdf.
13. ^ "Earthquake Storms". Horizon. 9pm 1 April 2003. http://www.bbc.co.uk/science/horizon/2003/earthquakestorms.shtml. Retrieved 2007-05-02.
14. ^ ^{a b} "Earthquake Facts". USGS. http://earthquake.usgs.gov/learn/facts.php. Retrieved 2010-04-25.
15. ^ ^{a b} Pressler, Margaret Webb (14 April 2010). "More earthquakes than usual? Not really.". KidsPost (Washington Post: Washington Post): pp. C10.
16. ^ "Earthquake Hazards Program". USGS. http://earthquake.usgs.gov/. Retrieved 2006-08-14.
17. ^ Seismicity and earthquake hazard in the UK
18. ^ "Italy's earthquake history". BBC News. October 31, 2002.
19. ^ "Common Myths about Earthquakes". USGS. http://earthquake.usgs.gov/learning/faq.php?categoryID=6&faqID=110. Retrieved 2006-08-14.
20. ^ "Earthquake Facts and Statistics: Are earthquakes increasing?". USGS. http://neic.usgs.gov/neis/eqlists/eqstats.html. Retrieved 2006-08-14.
21. ^ "Historic Earthquakes and Earthquake Statistics: Where do earthquakes occur?". USGS. http://earthquake.usgs.gov/learning/faq.php?categoryID=11&faqID=95. Retrieved 2006-08-14.
22. ^ "Visual Glossary - Ring of Fire". USGS. http://earthquake.usgs.gov/learning/glossary.php?termID=150. Retrieved 2006-08-14.
23. ^ "Global urban seismic risk". Cooperative Institute for Research in Environmental Science.
24. ^ Madrigal, Alexis (4 June 2008). "Top 5 Ways to Cause a Man-Made Earthquake". Wired News (CondéNet). http://blog.wired.com/wiredscience/2008/06/top-5-ways-that.html. Retrieved 2008-06-05.
25. ^ "How Humans Can Trigger Earthquakes". National Geographic. February 10, 2009. http://news.nationalgeographic.com/news/2009/02/photogalleries/humans-cause-earthquakes/photo2.html. Retrieved April 24, 2009.
26. ^ Brendan Trembath (January 9, 2007). "Researcher claims mining triggered 1989 Newcastle earthquake". Australian Broadcasting Corporation. http://www.abc.net.au/am/content/2007/s1823833.htm. Retrieved April 24, 2009.
27. ^ On Shaky Ground, Association of Bay Area Governments, San Francisco, reports 1995,1998 (updated 2003)
28. ^ Guidelines for evaluating the hazard of surface fault rupture, California Geological Survey
29. ^ "Natural Hazards - Landslides". USGS. http://www.usgs.gov/hazards/landslides/. Retrieved 2008-09-15.
30. ^ "The Great 1906 San Francisco earthquake of 1906". USGS. http://earthquake.usgs.gov/regional/nca/1906/18april/index.php. Retrieved 2008-09-15.
31. ^ "Historic Earthquakes -1946 Anchorage Earthquake". USGS. http://earthquake.usgs.gov/regional/states/events/1964_03_28.php. Retrieved 2008-09-15.
32. ^ ^{a b} Noson, Qamar, and Thorsen (1988). Washington Division of Geology and Earth Resources Information Circular 85. Washington State Earthquake Hazards.
33. ^ MSN Encarta Dictionary. Flood. Retrieved on 2006-12-28. Archived 2009-10-31.
34. ^ "Notes on Historical Earthquakes". British Geological Survey. http://www.quakes.bgs.ac.uk/earthquakes/historical/historical_listing.htm. Retrieved 2008-09-15.
35. ^ "Fresh alert over Tajik flood threat". BBC News. 2003-08-03. http://news.bbc.co.uk/2/hi/asia-pacific/3120693.stm. Retrieved 2008-09-15.
36. ^ Thomas, Amanda M.; Bürgmann, Roland; Nadeau, Robert M. (December 24, 2009). "Tremor-tide correlations and near-lithostatic pore pressure on the deep San Andreas fault". Nature 462 (7276): pp. 1048–1051. doi:10.1038/nature08654. PMID 20033046. http://www.nature.com/nature/journal/v462/n7276/full/nature08654.html. Retrieved December 29, 2009
37. ^ "Gezeitenkräfte: Sonne und Mond lassen Kalifornien erzittern" SPIEGEL online, 29.12.2009
38. ^ Tamrazyan, Gurgen P. (1967). "Tide-forming forces and earthquakes". ICARUS (Elsevier) 7: pp. 59–65
39. ^ Tamrazyan, Gurgen P. (1968). "Principal Regularities in the Distribution of Major Earthquakes Relative to Solar and Lunar Tides and Other Cosmic Forces". ICARUS (Elsevier) 9: pp. 574–592
40. ^ "Facts about The Year Without a Summer". National Geographic UK. http://www.discoverychannel.co.uk/earth/year_without_summer/facts/index.shtml.
41. ^ ^{a b c} Watson, John; Watson, Kathie (October 23, 1997). "Predicting Earthquakes". http://pubs.usgs.gov/gip/earthq1/predict.html. Retrieved May 9, 2009.
42. ^ NZSEE Bulletin 39(2)-June 2006
43. ^ ASCE-SEI 41
44. ^ NZSEE 2006
45. ^ ^{a b c d} "Earthquakes". Encyclopedia of World Environmental History. 1. Encyclopedia of World Environmental History. 2003. pp. 358–364.
46. ^ Sturluson, Snorri (1220). Prose Edda.
47. ^ Sellers, Paige (1997-03-03). "Poseidon". Encyclopedia Mythica. http://www.pantheon.org/articles/p/poseidon.html. Retrieved 2008-09-02.
48. ^ ^{a b c d} Van Riper, A. Bowdoin (2002). Science in popular culture: a reference guide. Westport: Greenwood Press. pp. 60. ISBN 0–313–31822–0.
49. ^ JM Appel. A Comparative Seismology. Weber Studies (first publication), Volume 18, Number 2.
50. ^ Goenjian, Najarian, Pynoos, Steinberg, Manoukian, Tavosian, Fairbanks (1994). Posttraumatic stress disorder in elderly and younger adults after the 1988 earthquake in Armenia. Am J Psychiatry 1994; 151:895-901.
51. ^ Wang, Gao, Shinfuku, Zhang, Zhao, Shen (2000). Longitudinal Study of Earthquake-Related PTSD in a Randomly Selected Community Sample in North China. Am J Psychiatry, 157(8): 1260 - 1266.
52. ^ Goenjian, Steinberg, Najarian, Fairbanks, Tashjian, Pynoos (2000).Prospective Study of Posttraumatic Stress, Anxiety, and Depressive Reactions After Earthquake and Political Violence. Am J Psychiatry, 157(6): 911 - 895.
53. ^ Coates SW, Schechter D (2004). Preschoolers’ traumatic stress post-9/11: relational and developmental perspectives. Disaster Psychiatry Issue. Psychiatric Clinics of North America, 27(3), 473-489.
54. ^ Schechter DS, Coates SW, First E (2002). Observations of acute reactions of young children and their families to the World Trade Center attacks. Journal of ZERO-TO-THREE: National Center for Infants, Toddlers, and Families, 22(3), 9-13.

General references

• Donald Hyndman, David Hyndman (2009). "Chapter 3: Earthquakes and their causes". Natural Hazards and Disasters (2nd ed.). Brooks/Cole: Cengage Learning. ISBN 0495316679. http://books.google.com/?id=8jg5oRWHXmcC&pg=PT54&q=.

External links

Educational

• How to survive an earthquake - Guide for children and youth
• Guide to earthquakes and plate tectonics
• Earthquakes — an educational booklet by Kaye M. Shedlock & Louis C. Pakiser
• The Severity of an Earthquake
• USGS Earthquake FAQs
• IRIS Seismic Monitor - maps all earthquakes in the past five years.
• Latest Earthquakes in the World - maps all earthquakes in the past week.
• Earthquake Information from the Deep Ocean Exploration Institute, Woods Hole Oceanographic Institution
• Geo.Mtu.Edu — How to locate an earthquake's epicenter
• Photos/images of historic earthquakes
• earthquakecountry.info Answers to FAQs about Earthquakes and Earthquake Preparedness
• Interactive guide: Earthquakes - an educational presentation by Guardian Unlimited
• Geowall — an educational 3D presentation system for looking at and understanding earthquake data
• Virtual Earthquake - educational site explaining how epicenters are located and magnitude is determined
• CBC Digital Archives — Canada's Earthquakes and Tsunamis
• Earthquakes Educational Resources - dmoz
• USGS: Earthquakes for Kids

Seismological data centers

Europe

• International Seismological Centre (ISC)
• European-Mediterranean Seismological Centre (EMSC)
• Global Seismic Monitor at GFZ Potsdam
• Global Earthquake Report – chart
• Earthquakes in Iceland during the last 48 hours
• Istituto Nazionale di Geofisica e Vulcanologia (INGV), Italy
• Database of Individual Seismogenic Sources (DISS), Central Mediterranean
• Portuguese Meteorological Institute (Seismic activity during the last month)

Japan

• Earthquake Information of Japan, Japan Meteorological Agency
• International Institute of Seismology and Earthquake Engineering (IISEE)
• Building Research Institute
• Database for the damage of world earthquake, ancient period (3000 BC) to year of 2006- Building Research Institute (Japan) (建築研究所) in Japanese
• Seismic activity in last 7 days - Weathernews Inc., indicated with circled shindo (震度）) scale, magnitude (M) and its location.
  • Weathernews Inc, Global web site

New Zealand

• GeoNet - New Zealand Earthquake Report (latest and recent quakes)

United States

• The U.S. National Earthquake Information Center
• Southern California Earthquake Data Center
• The Southern California Earthquake Center (SCEC)
• Broadband Seismic Data Collection Center, San Diego, California (ANZA network)
• Putting Down Roots in Earthquake Country An Earthquake Science and Preparedness Handbook produced by SCEC
• Recent earthquakes in California and Nevada
• Seismograms for recent earthquakes via REV, the Rapid Earthquake Viewer
• Incorporated Research Institutions for Seismology (IRIS), earthquake database and software
• IRIS Seismic Monitor - world map of recent earthquakes
• SeismoArchives - seismogram archives of significant earthquakes of the world

Seismic scales

• The European Macroseismic Scale

Scientific information

• "Earthquake Magnitudes and the Gutenberg-Richter Law". SimScience. http://simscience.org/crackling/Advanced/Earthquakes/GutenbergRichter.html. Retrieved 2006-08-14.
• Hiroo Kanamori, Emily E. Brodsky (June 2001). "The Physics of Earthquakes" (). Physics Today 54 (6): 34. doi:10.1063/1.1387590. http://www.physicstoday.org/pt/vol-54/iss-6/p34.html.

Miscellaneous

• Reports on China Sichuan earthquake 12/05/2008
• Kashmir Relief & Development Foundation (KRDF)
• PBS NewsHour - Predicting Earthquakes
• USGS – Largest earthquakes in the world since 1900
• The Destruction of Earthquakes - a list of the worst earthquakes ever recorded
• Los Angeles Earthquakes plotted on a Google map
• the EM-DAT International Disaster Database
• Earthquake Newspaper Articles Archive
• Earth-quake.org
• PetQuake.org- official PETSAAF system which relies on strange or atypical animal behavior to predict earthquakes.
• A series of earthquakes in southern Italy - 23 November 1980, Gesualdo
• Recent Quakes WorldWide
• Real-time earthquakes on Google Map, Australia and rest of the world
• Earthquake Information - detailed statistics and integrated with Google Maps and Google Earth
• Kharita - INGV portal for Digital Cartography - Last earthquakes recorded by INGV Italian Network (with Google Maps)
• Kharita - INGV portal for Digital Cartography - Italian Seismicity by region 1981-2006 (with Google Maps)
• Interactive world map, showing recent earthquakes (day/week/month) – Quake-Catcher Network, BOINC

Categories: Earthquakes | Seismology | Geological hazards | Earthquake engineering

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