Earthquake

An earthquake (also known as a quake, tremor or temblor) is the shaking of the surface of the Earth, resulting from the sudden release of energy in the Earth's lithosphere that creates seismic waves. Earthquakes can range in size from those that are so weak that they cannot be felt to those violent enough to toss people around and destroy whole cities. The seismicity, or seismic activity, of an area is the frequency, type and size of earthquakes experienced over a period of time. The word tremor is also used for non-earthquake seismic rumbling.

At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.

In its most general sense, the word earthquake is used to describe any seismic event—whether natural or caused by humans—that generates seismic waves. Earthquakes are caused mostly by rupture of geological faults, but also by other events such as volcanic activity, landslides, mine blasts, and nuclear tests. An earthquake's point of initial rupture is called its focus or hypocenter. The epicenter is the point at ground level directly above the hypocenter.

Quake epicenters 1963-98
Earthquake epicenters occur mostly along tectonic plate boundaries, and especially on the Pacific Ring of Fire.
Global plate motion 2008-04-17
Global plate tectonic movement

Naturally occurring earthquakes

Fault types
Three types of faults:
A. Strike-slip.
B. Normal.
C. Thrust.

Tectonic earthquakes occur anywhere in 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 along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities and this 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.[1] This energy is released as a combination of radiated elastic strain seismic waves, 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 growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy 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.[2]

Earthquake fault types

There are three main types of fault, all of which may cause an interplate 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 and movement on them involves a vertical component. Normal faults occur mainly in areas where the crust is being extended such as a divergent boundary. Reverse faults occur in areas where the crust is being shortened 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.

Reverse faults, particularly those along convergent plate boundaries are associated with the most powerful earthquakes, megathrust earthquakes, including almost all of those of magnitude 8 or more. Strike-slip faults, particularly continental transforms, can produce major earthquakes up to about magnitude 8. Earthquakes associated with normal faults are generally less than magnitude 7. For every unit increase in magnitude, there is a roughly thirtyfold increase in the energy released. For instance, an earthquake of magnitude 6.0 releases approximately 30 times more energy than a 5.0 magnitude earthquake and a 7.0 magnitude earthquake releases 900 times (30 × 30) more energy than a 5.0 magnitude of earthquake. An 8.6 magnitude earthquake releases the same amount of energy as 10,000 atomic bombs like those used in World War II.[3]

This is so because the energy released in an earthquake, and thus its magnitude, is proportional to the area of the fault that ruptures[4] and the stress drop. Therefore, the longer the length and the wider the width of the faulted area, the larger the resulting magnitude. The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending down into the hot mantle, are the only parts of our planet which can store elastic energy and release it in fault ruptures. Rocks hotter than about 300 °C (572 °F) flow in response to stress; they do not rupture in earthquakes.[5][6] The maximum observed lengths of ruptures and mapped faults (which may break in a single rupture) are approximately 1,000 km (620 mi). Examples are the earthquakes in Chile, 1960; Alaska, 1957; Sumatra, 2004, all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the San Andreas Fault (1857, 1906), the North Anatolian Fault in Turkey (1939) and the Denali Fault in Alaska (2002), are about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.

Kluft-photo-Carrizo-Plain-Nov-2007-Img 0327
Aerial photo of the San Andreas Fault in the Carrizo Plain, northwest of Los Angeles

The most important parameter controlling the maximum earthquake magnitude on a fault is however 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.[7] Thus the width of the plane within the top brittle crust of the Earth can become 50–100 km (31–62 mi) (Japan, 2011; Alaska, 1964), making the most powerful earthquakes possible.

Strike-slip faults tend to be oriented near vertically, resulting in an approximate width of 10 km (6.2 mi) within the brittle crust,[8] thus earthquakes with magnitudes much larger than 8 are not possible. 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 six kilometres (3.7 mi).[9][10]

In addition, there exists a hierarchy of stress level in the three fault types. Thrust faults are generated by the highest, strike slip by intermediate, and normal faults by the lowest stress levels.[11] 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 up, 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.

Earthquakes away from plate boundaries

Tremor(English)
Comparison of the 1985 and 2017 earthquakes on Mexico City, Puebla and Michoacán/Guerrero

Where plate boundaries occur within the continental lithosphere, deformation is spread out over a much larger area than the plate boundary itself. In the case of the San Andreas fault 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 was associated with movement on a blind thrust within such a zone. Another example is the strongly oblique convergent plate boundary between the Arabian and Eurasian plates where it runs through the northwestern part of 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.[12]

All tectonic plates have internal stress fields caused by their interactions with neighboring plates and sedimentary loading or unloading (e.g. deglaciation).[13] These stresses may be sufficient to cause failure along existing fault planes, giving rise to intraplate earthquakes.[14]

Shallow-focus and deep-focus earthquakes

HotelSanSalvador
Collapsed Gran Hotel building in the San Salvador metropolis, after the shallow 1986 San Salvador earthquake.

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 (43 mi) are classified as 'shallow-focus' earthquakes, while those with a focal-depth between 70 and 300 km (43 and 186 mi) are commonly termed 'mid-focus' or 'intermediate-depth' earthquakes. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, Deep-focus earthquakes may occur at much greater depths (ranging from 300 to 700 km (190 to 430 mi)).[15] These seismically active areas of subduction are known as Wadati–Benioff zones. Deep-focus earthquakes occur at a depth where the subducted lithosphere 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 undergoing a phase transition into a spinel structure.[16]

Earthquakes and volcanic activity

Earthquakes often occur in volcanic regions and are caused there, both by tectonic faults and the movement of magma in volcanoes. Such earthquakes can serve as an early warning of volcanic eruptions, as during the 1980 eruption of Mount St. Helens.[17] 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 that measures ground slope) and used as sensors to predict imminent or upcoming eruptions.[18]

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 (330 ft) 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.[19]

Rupture propagation is generally modeled using a fracture mechanics 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 neighboring coast, as in the 1896 Sanriku earthquake.[19]

Tidal forces

Tides may induce some seismicity, see tidal triggering of earthquakes for details.

Earthquake clusters

Most earthquakes form part of a sequence, related to each other in terms of location and time.[20] 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.[21]

Aftershocks

2016 Central Italy earthquake wide
Magnitude of the Central Italy earthquakes of August and October 2016, of January 2017 and the aftershocks (which continued to occur after the period shown here).

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.[20]

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.[22] In August 2012, a swarm of earthquakes shook Southern California's Imperial Valley, showing the most recorded activity in the area since the 1970s.[23]

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 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.[24][25]

Intensity of earth quaking and magnitude of earthquakes

Quaking or shaking of the earth is a common phenomenon undoubtedly known to humans from earliest times. Prior to the development of strong-motion accelerometers that can measure peak ground speed and acceleration directly, the intensity of the earth-shaking was estimated on the basis of the observed effects, as categorized on various seismic intensity scales. Only in the last century has the source of such shaking been identified as ruptures in the earth's crust, with the intensity of shaking at any locality dependent not only on the local ground conditions, but also on the strength or magnitude of the rupture, and on its distance.[26]

The first scale for measuring earthquake magnitudes was developed by Charles F. Richter in 1935. Subsequent scales (see seismic magnitude scales) 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.[27]

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.[28]

Frequency of occurrence

It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt.[29][30] Minor earthquakes occur nearly constantly around the world in places like California and Alaska in the U.S., as well as in El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia, Iran, Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, India, Nepal and Japan, but earthquakes can occur almost anywhere, including Downstate New York, England, and Australia.[31] 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.[32] 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.[33] This is an example of the Gutenberg–Richter law.

Comerio, Luca (1878-1940) - Vittime del terremoto di Messina (dicembre 1908)
The Messina earthquake and tsunami took as many as 200,000 lives on December 28, 1908 in Sicily and Calabria.[34]

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 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.[35] In recent years, the number of major earthquakes per year has decreased, though this is probably a statistical fluctuation rather than a systematic trend.[36] More detailed statistics on the size and frequency of earthquakes is available from the United States Geological Survey (USGS).[37] 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.[38]

Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000-kilometre (25,000 mi) 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.[39][40] Massive earthquakes tend to occur along other plate boundaries, too, such as along the Himalayan Mountains.[41]

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 three million people.[42]

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: storing large amounts of water behind a dam (and possibly building an extremely heavy building), drilling and injecting liquid into wells, and by coal mining and oil drilling.[43] 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.[44]

The greatest earthquake in Australia's history is also claimed to be induced by human activity: Newcastle, Australia was built over a large sector of coal mining areas. The earthquake has been reported to be spawned from a fault that reactivated due to the millions of tonnes of rock removed in the mining process.[45]

Measuring and locating earthquakes

The instrumental scales used to describe the size of an earthquake began with the Richter magnitude scale 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 travel through the Earth's interior and can be recorded by seismometers at great distances. The surface wave magnitude was developed in the 1950s as a means to measure remote earthquakes and to improve the accuracy for larger events. The moment magnitude scale measures the amplitude of the shock, but also takes into account the seismic moment (total rupture area, average slip of the fault, and rigidity of the rock). The Japan Meteorological Agency seismic intensity scale, the Medvedev–Sponheuer–Karnik scale, and the Mercalli intensity scale are based on the observed effects and are related to the intensity of shaking.

Every tremor produces different types of seismic waves, which travel through rock with different velocities:

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 epicenter 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 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 times 8.[46] Slight deviations are caused by inhomogeneities of subsurface structure. By such analyses of seismograms the Earth's core was located in 1913 by Beno Gutenberg.

S waves and later arriving surface waves do main damage compared to P waves. P wave squeezes and expands material in the same direction it is traveling. S wave shakes the ground up and down and back and forth.[47]

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.

Standard reporting of earthquakes includes its magnitude, date and time of occurrence, geographic coordinates of its epicenter, depth of the epicenter, geographical region, distances to population centers, location uncertainty, a number of parameters that are included in USGS earthquake reports (number of stations reporting, number of observations, etc.), and a unique event ID.[48]

Although relatively slow seismic waves have traditionally been used to detect earthquakes, scientists realized in 2016 that gravitational measurements could provide instantaneous detection of earthquakes, and confirmed this by analyzing gravitational records associated with the 2011 Tohoku-Oki ("Fukushima") earthquake.[49][50]

Effects of earthquakes

1755 Lisbon earthquake
1755 copper engraving depicting Lisbon in ruins and in flames after the 1755 Lisbon earthquake, which killed an estimated 60,000 people. A tsunami overwhelms the ships in the harbor.

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

Shaking and ground rupture

Haiti earthquake damage
Damaged buildings in Port-au-Prince, Haiti, January 2010.

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.[51] 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 meters 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 which are likely to break the ground surface within the life of the structure.[52]

Landslides

Earthquakes can produce slope instability leading to landslides, a major geological hazard. Landslide danger may persist while emergency personnel are attempting rescue.[53]

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.[54]

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. For example, in the 1964 Alaska earthquake, soil liquefaction caused many buildings to sink into the ground, eventually collapsing upon themselves.[55]

Tsunami

2004-tsunami
The tsunami of the 2004 Indian Ocean earthquake

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 100 kilometers (62 mi), 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.[56]

Ordinarily, subduction earthquakes under magnitude 7.5 on the Richter magnitude 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.[56]

Floods

Floods may be secondary effects of earthquakes, if dams are damaged. Earthquakes may cause landslips to dam rivers, which collapse and cause floods.[57]

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.[58]

Human impacts

Ghajn Hadid Tower closer view
Ruins of the Għajn Ħadid Tower, which collapsed in an earthquake in 1856

An earthquake may cause injury and loss of life, road and bridge damage, general property damage, and collapse or destabilization (potentially leading to future collapse) of buildings. The aftermath may bring disease, lack of basic necessities, mental consequences such as panic attacks, depression to survivors,[59] and higher insurance premiums.

Major earthquakes

Map of earthquakes 1900-
Earthquakes (M6.0+) since 1900 through 2017
USGS magnitude 8 earthquakes since 1900
Earthquakes of magnitude 8.0 and greater since 1900. The apparent 3D volumes of the bubbles are linearly proportional to their respective fatalities.[60]

One of the most devastating earthquakes in recorded history was the 1556 Shaanxi earthquake, which occurred on 23 January 1556 in Shaanxi province, China. More than 830,000 people died.[61] Most houses in the area were yaodongs—dwellings carved out of loess hillsides—and many victims were killed when these structures collapsed. The 1976 Tangshan earthquake, which killed between 240,000 and 655,000 people, was the deadliest of the 20th century.[62]

The 1960 Chilean earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960.[29][30] Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday earthquake (March 27, 1964) which was centered in Prince William Sound, Alaska.[63][64] The ten largest recorded earthquakes have all been megathrust earthquakes; however, of these ten, only the 2004 Indian Ocean earthquake 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 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.

Prediction

Earthquake prediction is a branch of the science of seismology concerned with the specification of the time, location, and magnitude of future earthquakes within stated limits.[65] Many methods have been developed for predicting the time and place in which earthquakes will occur. Despite considerable research efforts by seismologists, scientifically reproducible predictions cannot yet be made to a specific day or month.[66]

Forecasting

While forecasting is usually considered to be a type of prediction, earthquake forecasting is often differentiated from earthquake prediction. Earthquake forecasting is concerned with the probabilistic assessment of general earthquake hazard, including the frequency and magnitude of damaging earthquakes in a given area over years or decades.[67] For well-understood faults the probability that a segment may rupture during the next few decades can be estimated.[68][69]

Earthquake warning systems 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 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 can provide building owners with financial protection against losses resulting from earthquakes Emergency management strategies can be employed by a government or organization to mitigate risks and prepare for consequences.

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 shaking starts. For areas near large bodies of water, earthquake preparedness encompasses the possibility of a tsunami caused by a large quake.

Historical views

Lycosthène
An image from a 1557 book depicting an earthquake in Italy in the 4th century BCE

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."[70] Thales of Miletus (625–547 BCE) was the only documented person who believed that earthquakes were caused by tension between the earth and water.[70] 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 (460–371 BCE) blamed water in general for earthquakes.[70] Pliny the Elder called earthquakes "underground thunderstorms."[70]

Recent studies

In recent studies, geologists claim that global warming is one of the reasons for increased seismic activity. According to these studies melting glaciers and rising sea levels disturb the balance of pressure on Earth's tectonic plates thus causing increase in the frequency and intensity of earthquakes.[71]

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 dripped on Loki's face, forcing him to jerk his head away and thrash against his bonds, which caused the earth to tremble.[72]

In Greek mythology, Poseidon was the cause and god of earthquakes. When he was in a bad mood, he struck the ground with a trident, causing earthquakes and other calamities. He also used earthquakes to punish and inflict fear upon people as revenge.[73]

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.[74]

In 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.[75] Fictional earthquakes tend to strike suddenly and without warning.[75] 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).[75] 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), Goodbye California (1977), 2012 (2009) and San Andreas (2015) among other works.[75] 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.[76]

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.[77] 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.[78][79] 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 even more important to their emotional and physical health than the simple giving of provisions.[80] As was observed after other disasters involving destruction and loss of life and their media depictions, 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.[81]

See also

References

  1. ^ Ohnaka, M. (2013). The Physics of Rock Failure and Earthquakes. Cambridge University Press. p. 148. ISBN 978-1-107-35533-0.
  2. ^ Spence, William; S.A. Sipkin; G.L. Choy (1989). "Measuring the Size of an Earthquake". United States Geological Survey. Archived from the original on 2009-09-01. Retrieved 2006-11-03.
  3. ^ Geoscience Australia
  4. ^ Wyss, M. (1979). "Estimating expectable maximum magnitude of earthquakes from fault dimensions". Geology. 7 (7): 336–340. Bibcode:1979Geo.....7..336W. doi:10.1130/0091-7613(1979)7<336:EMEMOE>2.0.CO;2.
  5. ^ Sibson R.H. (1982) "Fault Zone Models, Heat Flow, and the Depth Distribution of Earthquakes in the Continental Crust of the United States", Bulletin of the Seismological Society of America, Vol 72, No. 1, pp. 151–163
  6. ^ Sibson, R.H. (2002) "Geology of the crustal earthquake source" International handbook of earthquake and engineering seismology, Volume 1, Part 1, p. 455, eds. W H K Lee, H Kanamori, P C Jennings, and C. Kisslinger, Academic Press, ISBN 978-0-12-440652-0
  7. ^ "Global Centroid Moment Tensor Catalog". Globalcmt.org. Retrieved 2011-07-24.
  8. ^ "Instrumental California Earthquake Catalog". WGCEP. Archived from the original on 2011-07-25. Retrieved 2011-07-24.
  9. ^ Hjaltadóttir S., 2010, "Use of relatively located microearthquakes to map fault patterns and estimate the thickness of the brittle crust in Southwest Iceland"
  10. ^ "Reports and publications | Seismicity | Icelandic Meteorological office". En.vedur.is. Retrieved 2011-07-24.
  11. ^ Schorlemmer, D.; Wiemer, S.; Wyss, M. (2005). "Variations in earthquake-size distribution across different stress regimes". Nature. 437 (7058): 539–542. Bibcode:2005Natur.437..539S. doi:10.1038/nature04094. PMID 16177788.
  12. ^ Talebian, M; Jackson, J (2004). "A reappraisal of earthquake focal mechanisms and active shortening in the Zagros mountains of Iran". Geophysical Journal International. 156 (3): 506–526. Bibcode:2004GeoJI.156..506T. doi:10.1111/j.1365-246X.2004.02092.x.
  13. ^ Nettles, M.; Ekström, G. (May 2010). "Glacial Earthquakes in Greenland and Antarctica". Annual Review of Earth and Planetary Sciences. 38 (1): 467–491. Bibcode:2010AREPS..38..467N. doi:10.1146/annurev-earth-040809-152414.
  14. ^ 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.CS1 maint: Multiple names: authors list (link)
  15. ^ "M7.5 Northern Peru Earthquake of 26 September 2005" (PDF). National Earthquake Information Center. 17 October 2005. Retrieved 2008-08-01.
  16. ^ Greene II, H.W.; Burnley, P.C. (October 26, 1989). "A new self-organizing mechanism for deep-focus earthquakes". Nature. 341 (6244): 733–737. Bibcode:1989Natur.341..733G. doi:10.1038/341733a0.
  17. ^ Foxworthy and Hill (1982). Volcanic Eruptions of 1980 at Mount St. Helens, The First 100 Days: USGS Professional Paper 1249.
  18. ^ Watson, John; Watson, Kathie (January 7, 1998). "Volcanoes and Earthquakes". United States Geological Survey. Retrieved May 9, 2009.
  19. ^ 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, DC: National Academies Press. p. 418. ISBN 978-0-309-06562-7. Retrieved 8 July 2010.
  20. ^ a b "What are Aftershocks, Foreshocks, and Earthquake Clusters?". Archived from the original on 2009-05-11.
  21. ^ "Repeating Earthquakes". United States Geological Survey. January 29, 2009. Retrieved May 11, 2009.
  22. ^ "Earthquake Swarms at Yellowstone". United States Geological Survey. Retrieved 2008-09-15.
  23. ^ Duke, Alan. "Quake 'swarm' shakes Southern California". CNN. Retrieved 27 August 2012.
  24. ^ Amos Nur; Cline, Eric H. (2000). "Poseidon's Horses: Plate Tectonics and Earthquake Storms in the Late Bronze Age Aegean and Eastern Mediterranean" (PDF). Journal of Archaeological Science. 27 (1): 43–63. doi:10.1006/jasc.1999.0431. ISSN 0305-4403. Archived from the original (PDF) on 2009-03-25.
  25. ^ "Earthquake Storms". Horizon. 1 April 2003. Retrieved 2007-05-02.
  26. ^ Bolt 1993.
  27. ^ Chung & Bernreuter 1980, p. 1.
  28. ^ The USGS policy for reporting magnitudes to the press was posted at USGS policy Archived 2016-05-04 at the Wayback Machine, but has been removed. A copy can be found at http://dapgeol.tripod.com/usgsearthquakemagnitudepolicy.htm.
  29. ^ a b "Earthquake Facts". United States Geological Survey. Retrieved 2010-04-25.
  30. ^ a b Pressler, Margaret Webb (14 April 2010). "More earthquakes than usual? Not really". KidsPost. Washington Post: Washington Post. pp. C10.
  31. ^ "Earthquake Hazards Program". United States Geological Survey. Retrieved 2006-08-14.
  32. ^ USGS Earthquake statistics table based on data since 1900 Archived 2010-05-24 at the Wayback Machine
  33. ^ "Seismicity and earthquake hazard in the UK". Quakes.bgs.ac.uk. Retrieved 2010-08-23.
  34. ^ "Italy's earthquake history." BBC News. October 31, 2002.
  35. ^ "Common Myths about Earthquakes". United States Geological Survey. Archived from the original on 2006-09-25. Retrieved 2006-08-14.
  36. ^ Are Earthquakes Really on the Increase? Archived 2014-06-30 at the Wayback Machine, USGS Science of Changing World. Retrieved 30 May 2014.
  37. ^ "Earthquake Facts and Statistics: Are earthquakes increasing?". United States Geological Survey. Archived from the original on 2006-08-12. Retrieved 2006-08-14.
  38. ^ The 10 biggest earthquakes in history, Australian Geographic, March 14, 2011.
  39. ^ "Historic Earthquakes and Earthquake Statistics: Where do earthquakes occur?". United States Geological Survey. Archived from the original on 2006-09-25. Retrieved 2006-08-14.
  40. ^ "Visual Glossary – Ring of Fire". United States Geological Survey. Archived from the original on 2006-08-28. Retrieved 2006-08-14.
  41. ^ Jackson, James, "Fatal attraction: living with earthquakes, the growth of villages into megacities, and earthquake vulnerability in the modern world," Philosophical Transactions of the Royal Society, doi:10.1098/rsta.2006.1805 Phil. Trans. R. Soc. A 15 August 2006 vol. 364 no. 1845 1911–1925.
  42. ^ "Global urban seismic risk." Cooperative Institute for Research in Environmental Science.
  43. ^ Madrigal, Alexis (4 June 2008). "Top 5 Ways to Cause a Man-Made Earthquake". Wired News. CondéNet. Retrieved 2008-06-05.
  44. ^ "How Humans Can Trigger Earthquakes". National Geographic. February 10, 2009. Retrieved April 24, 2009.
  45. ^ Brendan Trembath (January 9, 2007). "Researcher claims mining triggered 1989 Newcastle earthquake". Australian Broadcasting Corporation. Retrieved April 24, 2009.
  46. ^ "Speed of Sound through the Earth". Hypertextbook.com. Retrieved 2010-08-23.
  47. ^ "Newsela | The science of earthquakes". newsela.com. Retrieved 2017-02-28.
  48. ^ Geographic.org. "Magnitude 8.0 - SANTA CRUZ ISLANDS Earthquake Details". Global Earthquake Epicenters with Maps. Retrieved 2013-03-13.
  49. ^ "Earth's gravity offers earlier earthquake warnings". Retrieved 2016-11-22.
  50. ^ "Gravity shifts could sound early earthquake alarm". Retrieved 2016-11-23.
  51. ^ "On Shaky Ground, Association of Bay Area Governments, San Francisco, reports 1995,1998 (updated 2003)". Abag.ca.gov. Archived from the original on 2009-09-21. Retrieved 2010-08-23.
  52. ^ "Guidelines for evaluating the hazard of surface fault rupture, California Geological Survey" (PDF). California Department of Conservation. 2002. Archived from the original (PDF) on 2009-10-09.
  53. ^ "Natural Hazards – Landslides". United States Geological Survey. Retrieved 2008-09-15.
  54. ^ "The Great 1906 San Francisco earthquake of 1906". United States Geological Survey. Retrieved 2008-09-15.
  55. ^ "Historic Earthquakes – 1964 Anchorage Earthquake". United States Geological Survey. Archived from the original on 2011-06-23. Retrieved 2008-09-15.
  56. ^ a b Noson, Qamar, and Thorsen (1988). Washington Division of Geology and Earth Resources Information Circular 85. Washington State Earthquake Hazards.CS1 maint: Multiple names: authors list (link)
  57. ^ "Notes on Historical Earthquakes". British Geological Survey. Archived from the original on 2011-05-16. Retrieved 2008-09-15.
  58. ^ "Fresh alert over Tajik flood threat". BBC News. 2003-08-03. Retrieved 2008-09-15.
  59. ^ "Earthquake Resources". Nctsn.org. Retrieved 2018-06-05.
  60. ^ USGS: Magnitude 8 and Greater Earthquakes Since 1900 Archived 2016-04-14 at the Wayback Machine
  61. ^ "Earthquakes with 50,000 or More Deaths Archived November 2, 2009, at the Wayback Machine". U.S. Geological Survey
  62. ^ Spignesi, Stephen J. (2005). Catastrophe!: The 100 Greatest Disasters of All Time. ISBN 0-8065-2558-4
  63. ^ Kanamori Hiroo. "The Energy Release in Great Earthquakes" (PDF). Journal of Geophysical Research. Archived from the original (PDF) on 2010-07-23. Retrieved 2010-10-10.
  64. ^ USGS. "How Much Bigger?". United States Geological Survey. Retrieved 2010-10-10.
  65. ^ Geller et al. 1997, p. 1616, following Allen (1976, p. 2070), who in turn followed Wood & Gutenberg (1935)
  66. ^ Earthquake Prediction. Ruth Ludwin, U.S. Geological Survey.
  67. ^ Kanamori 2003, p. 1205. See also International Commission on Earthquake Forecasting for Civil Protection 2011, p. 327.
  68. ^ Working Group on California Earthquake Probabilities in the San Francisco Bay Region, 2003 to 2032, 2003, "Archived copy". Archived from the original on 2017-02-18. Retrieved 2017-08-28.CS1 maint: Archived copy as title (link)
  69. ^ Pailoplee, Santi (2017-03-13). "Probabilities of Earthquake Occurrences along the Sumatra-Andaman Subduction Zone". Open Geosciences. 9 (1): 4. Bibcode:2017OGeo....9....4P. doi:10.1515/geo-2017-0004. ISSN 2391-5447.
  70. ^ a b c d "Earthquakes". Encyclopedia of World Environmental History. 1: A–G. Routledge. 2003. pp. 358–364.
  71. ^ "Fire and Ice: Melting Glaciers Trigger Earthquakes, Tsunamis and Volcanos". about News. Retrieved October 27, 2015.
  72. ^ Sturluson, Snorri (1220). Prose Edda. ISBN 978-1-156-78621-5.
  73. ^ George E. Dimock (1990). The Unity of the Odyssey. Univ of Massachusetts Press. pp. 179–. ISBN 978-0-87023-721-8.
  74. ^ "Namazu". Ancient History Encyclopedia. Retrieved 2017-07-23.
  75. ^ a b c d Van Riper, A. Bowdoin (2002). Science in popular culture: a reference guide. Westport: Greenwood Press. p. 60. ISBN 978-0-313-31822-1.
  76. ^ JM Appel. A Comparative Seismology. Weber Studies (first publication), Volume 18, Number 2.
  77. ^ Goenjian, Najarian; Pynoos, Steinberg; Manoukian, Tavosian; Fairbanks, AM; Manoukian, G; Tavosian, A; Fairbanks, LA (1994). "Posttraumatic stress disorder in elderly and younger adults after the 1988 earthquake in Armenia". Am J Psychiatry. 151 (6): 895–901. doi:10.1176/ajp.151.6.895. PMID 8185000.
  78. ^ Wang, Gao; Shinfuku, Zhang; Zhao, Shen; Zhang, H; Zhao, C; Shen, Y (2000). "Longitudinal Study of Earthquake-Related PTSD in a Randomly Selected Community Sample in North China". Am J Psychiatry. 157 (8): 1260–1266. doi:10.1176/appi.ajp.157.8.1260. PMID 10910788.
  79. ^ Goenjian, Steinberg; Najarian, Fairbanks; Tashjian, Pynoos (2000). "Prospective Study of Posttraumatic Stress, Anxiety, and Depressive Reactions After Earthquake and Political Violence" (PDF). Am J Psychiatry. 157 (6): 911–916. doi:10.1176/appi.ajp.157.6.911. PMID 10831470. Archived from the original (PDF) on 2017-08-10.
  80. ^ 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. doi:10.1016/j.psc.2004.03.006. PMID 15325488.
  81. ^ 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.

External links

1755 Lisbon earthquake

The 1755 Lisbon earthquake, also known as the Great Lisbon earthquake, occurred in the Kingdom of Portugal on the morning of Saturday, 1 November, Feast of All Saints, at around 09:40 local time. In combination with subsequent fires and a tsunami, the earthquake almost totally destroyed Lisbon and adjoining areas. Seismologists today estimate the Lisbon earthquake had a magnitude in the range 8.5–9.0 on the moment magnitude scale, with its epicentre in the Atlantic Ocean about 200 km (120 mi) west-southwest of Cape St. Vincent. Chronologically it was the third known large scale earthquake to hit the city (one in 1321 and another in 1531). Estimates place the death toll in Lisbon alone between 10,000 and 100,000 people, making it one of the deadliest earthquakes in history.

The earthquake accentuated political tensions in the Kingdom of Portugal and profoundly disrupted the country's colonial ambitions. The event was widely discussed and dwelt upon by European Enlightenment philosophers, and inspired major developments in theodicy. As the first earthquake studied scientifically for its effects over a large area, it led to the birth of modern seismology and earthquake engineering.

1906 San Francisco earthquake

The 1906 San Francisco earthquake struck the coast of Northern California at 5:12 a.m. on Wednesday, April 18 with an estimated moment magnitude of 7.9 and a maximum Mercalli intensity of XI (Extreme). High intensity shaking was felt from Eureka on the North Coast to the Salinas Valley, an agricultural region to the south of the San Francisco Bay Area. Devastating fires soon broke out in the city and lasted for several days. Thousands of homes were dismantled. As a result, up to 3,000 people died and over 80% of the city of San Francisco was destroyed. The events are remembered as one of the worst and deadliest earthquakes in the history of the United States. The death toll remains the greatest loss of life from a natural disaster in California's history and high in the lists of American disasters.

1923 Great Kantō earthquake

The Great Kantō earthquake (関東大地震, Kantō dai-jishin) struck the Kantō Plain on the Japanese main island of Honshū at 11:58:44 JST (02:58:44 UTC) on Saturday, September 1, 1923. Varied accounts indicate the duration of the earthquake was between four and ten minutes.The earthquake had a magnitude of 7.9 on the moment magnitude scale (Mw ), with its focus deep beneath Izu Ōshima Island in Sagami Bay. The cause was a rupture of part of the convergent boundary where the Philippine Sea Plate is subducting beneath the Okhotsk Plate along the line of the Sagami Trough.

1960 Valdivia earthquake

The 1960 Valdivia earthquake (Spanish: Terremoto de Valdivia) or the Great Chilean earthquake (Gran terremoto de Chile) of 22 May is the most powerful earthquake ever recorded. Various studies have placed it at 9.4–9.6 on the moment magnitude scale. It occurred in the afternoon (19:11 GMT, 15:11 local time), and lasted approximately 10 minutes. The resulting tsunami affected southern Chile, Hawaii, Japan, the Philippines, eastern New Zealand, southeast Australia and the Aleutian Islands.

The epicenter of this megathrust earthquake was near Lumaco, approximately 570 kilometres (350 mi) south of Santiago, with Valdivia being the most affected city. The tremor caused localised tsunamis that severely battered the Chilean coast, with waves up to 25 metres (82 ft). The main tsunami raced across the Pacific Ocean and devastated Hilo, Hawaii. Waves as high as 10.7 metres (35 ft) were recorded 10,000 kilometres (6,200 mi) from the epicenter, and as far away as Japan and the Philippines.

The death toll and monetary losses arising from this widespread disaster are not certain.

Various estimates of the total number of fatalities from the earthquake and tsunamis have been published, ranging between 1,000 and 7,000 killed. Different sources have estimated the monetary cost ranged from US$400 million to 800 million (or $3.39 billion to $6.78 billion today, adjusted for inflation).

1989 Loma Prieta earthquake

The 1989 Loma Prieta earthquake occurred in Northern California on October 17 at 5:04 p.m. local time (1989-10-18 00:04 UTC). The shock was centered in The Forest of Nisene Marks State Park approximately 10 mi (16 km) northeast of Santa Cruz on a section of the San Andreas Fault System and was named for the nearby Loma Prieta Peak in the Santa Cruz Mountains. With an Mw magnitude of 6.9 and a maximum Modified Mercalli intensity of IX (Violent), the shock was responsible for 63 deaths and 3,757 injuries. The Loma Prieta segment of the San Andreas Fault System had been relatively inactive since the 1906 San Francisco earthquake (to the degree that it was designated a seismic gap) until two moderate foreshocks occurred in June 1988 and again in August 1989.

Damage was heavy in Santa Cruz County and less so to the south in Monterey County, but effects extended well to the north into the San Francisco Bay Area, both on the San Francisco Peninsula and across the bay in Oakland. No surface faulting occurred, though a large number of other ground failures and landslides were present, especially in the Summit area of the Santa Cruz Mountains. Liquefaction was also a significant issue, especially in the heavily damaged Marina District of San Francisco, but its effects were also seen in the East Bay, and near the shore of Monterey Bay, where a non-destructive tsunami was also observed.

Due to the sports coverage of the 1989 World Series, it became the first major earthquake in the United States that was broadcast live on national television (and as a result is sometimes referred to as the "World Series earthquake"). Rush-hour traffic on the Bay Area freeways was lighter than normal because the game, being played at Candlestick Park in San Francisco, was about to begin, and this may have prevented a larger loss of life, as several of the Bay Area's major transportation structures suffered catastrophic failures. The collapse of a section of the double-deck Nimitz Freeway in Oakland was the site of the largest number of casualties for the event, but the collapse of man-made structures and other related accidents contributed to casualties occurring in San Francisco, Los Altos, and Santa Cruz.

1994 Northridge earthquake

The 1994 Northridge earthquake was a magnitude of 6.7 (Mw), blind thrust earthquake that occurred on January 17 at 4:30:55 a.m. PST in the San Fernando Valley region of the County of Los Angeles. Its epicenter was in Reseda, a neighborhood in the north-central Valley. The quake had a duration of approximately 10–20 seconds, and its peak ground acceleration of 1.8g (16.7 m/s2) was the highest ever instrumentally recorded in an urban area in North America. Strong ground motion was felt as far away as Las Vegas, Nevada, about 220 miles (360 km) from the epicenter. The peak ground velocity at the Rinaldi Receiving Station was 183 cm/s (4.09 mph or 6.59 km/h), the fastest ever recorded.

Two 6.0 Mw  aftershocks followed, the first about one minute after the initial event and the second approximately 11 hours later, the strongest of several thousand aftershocks in all. The death toll was 57, with more than 8,700 injured. In addition, property damage was estimated to be $13–50 billion (equivalent to $22–85 billion today), making it one of the costliest natural disasters in U.S. history.

2004 Indian Ocean earthquake and tsunami

The 2004 Indian Ocean earthquake occurred at 00:58:53 UTC on 26 December, with an epicentre off the west coast of northern Sumatra. It was an undersea megathrust earthquake that registered a magnitude of 9.1–9.3 Mw, reaching a Mercalli intensity up to IX in certain areas. The earthquake was caused by a rupture along the fault between the Burma Plate and the Indian Plate.

A series of large tsunamis up to 30 metres (100 ft) high were created by the underwater seismic activity that became known collectively as the Boxing Day tsunamis. Communities along the surrounding coasts of the Indian Ocean were seriously affected, and the tsunamis killed an estimated 227,898 people in 14 countries. The Indonesian city of Banda Aceh reported the largest number of victims. The earthquake was one of the deadliest natural disasters in recorded history. The direct results caused major disruptions to living conditions and commerce particularly in Indonesia, Sri Lanka, India, and Thailand.

The earthquake was the third largest ever recorded and had the longest duration of faulting ever observed; between eight and ten minutes. It caused the planet to vibrate as much as 1 centimetre (0.4 inches), and it remotely triggered earthquakes as far away as Alaska. Its epicentre was between Simeulue and mainland Sumatra. The plight of the affected people and countries prompted a worldwide humanitarian response, with donations totaling more than US$14 billion. The event is known by the scientific community as the Sumatra–Andaman earthquake.

2008 Sichuan earthquake

The 2008 Sichuan earthquake (Chinese: 汶川大地震; pinyin: Wènchuān dà dìzhèn; literally: 'Great Wenchuan earthquake'), also known as the Great Sichuan earthquake or Wenchuan earthquake, occurred at 14:28:01 China Standard Time on May 12, 2008. Measuring at 8.0 Ms (7.9 Mw), the earthquake's epicenter was located 80 kilometres (50 mi) west-northwest of Chengdu, the provincial capital, with a focal depth of 19 km (12 mi). The earthquake ruptured the fault for over 240 km (150 mi), with surface displacements of several meters. The earthquake was also felt in nearby countries and as far away as both Beijing and Shanghai—1,500 and 1,700 km (930 and 1,060 mi) away—where office buildings swayed with the tremor. Strong aftershocks, some exceeding 6 Ms, continued to hit the area up to several months after the main shock, causing further casualties and damage. The earthquake also caused the largest number of geohazards ever recorded, including about 200,000 landslides and more than 800 quake lakes distributed over an area of 110,000 km2 (42,000 sq mi).Over 69,000 people lost their lives in the quake, including 68,636 in Sichuan province. 374,176 were reported injured, with 18,222 listed as missing as of July 2008. The geohazards triggered by the earthquake are thought to be responsible for at least one third of the death toll. The earthquake left about 4.8 million people homeless, though the number could be as high as 11 million. Approximately 15 million people lived in the affected area. It was the deadliest earthquake to hit China since the 1976 Tangshan earthquake, which killed at least 240,000 people, and the strongest in the country since the 1950 Chayu earthquake, which registered at 8.5 on the Richter magnitude scale. It is the 18th deadliest earthquake of all time. On November 6, 2008, the central government announced that it would spend 1 trillion RMB (about US $146.5 billion) over the next three years to rebuild areas ravaged by the earthquake, as part of the Chinese economic stimulus program.

2010 Haiti earthquake

The 2010 Haiti earthquake (French: Séisme de 2010 à Haïti; Haitian Creole: Tranblemanntè 12 janvye 2010 nan peyi Ayiti) was a catastrophic magnitude 7.0 Mw earthquake, with an epicenter near the town of Léogâne (Ouest) and approximately 25 kilometres (16 mi) west of Port-au-Prince, Haiti's capital. The earthquake occurred at 16:53 local time (21:53 UTC) on Tuesday, 12 January 2010.By 24 January, at least 52 aftershocks measuring 4.5 or greater had been recorded. An estimated three million people were affected by the quake. Death toll estimates range from 100,000 to about 160,000 to Haitian government figures from 220,000 to 316,000, although these latter figures are a matter of some dispute. The government of Haiti estimated that 250,000 residences and 30,000 commercial buildings had collapsed or were severely damaged. The nation's history of national debt, prejudicial trade policies by other countries, and foreign intervention into national affairs, contributed to the existing poverty and poor housing conditions that increased the death toll from the disaster.The earthquake caused major damage in Port-au-Prince, Jacmel and other cities in the region. Notable landmark buildings were significantly damaged or destroyed, including the Presidential Palace, the National Assembly building, the Port-au-Prince Cathedral, and the main jail. Among those killed were Archbishop of Port-au-Prince Joseph Serge Miot, and opposition leader Micha Gaillard. The headquarters of the United Nations Stabilization Mission in Haiti (MINUSTAH), located in the capital, collapsed, killing many, including the Mission's Chief, Hédi Annabi.Many countries responded to appeals for humanitarian aid, pledging funds and dispatching rescue and medical teams, engineers and support personnel. Communication systems, air, land, and sea transport facilities, hospitals, and electrical networks had been damaged by the earthquake, which hampered rescue and aid efforts; confusion over who was in charge, air traffic congestion, and problems with prioritising flights further complicated early relief work. Port-au-Prince's morgues were overwhelmed with tens of thousands of bodies. These had to be buried in mass graves.As rescues tailed off, supplies, medical care and sanitation became priorities. Delays in aid distribution led to angry appeals from aid workers and survivors, and looting and sporadic violence were observed. On 22 January, the United Nations noted that the emergency phase of the relief operation was drawing to a close, and on the following day, the Haitian government officially called off the search for survivors.

2011 Christchurch earthquake

An Mw 6.2 earthquake occurred in Christchurch on 22 February 2011 at 12:51 p.m. local time (23:51 UTC, 21 February). The earthquake struck the Canterbury Region in New Zealand's South Island and was centred two kilometres (1.2 mi) west of the port town of Lyttelton, and 10 kilometres (6 mi) south-east of the centre of Christchurch, at the time New Zealand's second-most populous city. The earthquake caused widespread damage across Christchurch, killing 185 people in the nation's fifth-deadliest disaster.

Christchurch's central city and eastern suburbs were badly affected, with damage to buildings and infrastructure already weakened by the magnitude 7.1 Canterbury earthquake of 4 September 2010 and its aftershocks. Significant liquefaction affected the eastern suburbs, producing around 400,000 tonnes of silt. The earthquake was felt across the South Island and parts of the lower and central North Island. While the initial quake only lasted for approximately 10 seconds, the damage was severe because of the location and shallowness of the earthquake's focus in relation to Christchurch as well as previous quake damage. Subsequent population loss saw the Christchurch main urban area fall behind the Wellington equivalent to decrease from second to third most populous area in New Zealand.

2011 Tōhoku earthquake and tsunami

The 2011 earthquake off the Pacific coast of Tōhoku (東北地方太平洋沖地震, Tōhoku-chihō Taiheiyō Oki Jishin) was a magnitude 9.0–9.1 (Mw) undersea megathrust earthquake off the coast of Japan that occurred at 14:46 JST (05:46 UTC) on Friday 11 March 2011, with the epicentre approximately 70 kilometres (43 mi) east of the Oshika Peninsula of Tōhoku and the hypocenter at an underwater depth of approximately 29 km (18 mi).

The earthquake is often referred to in Japan as the Great East Japan Earthquake (東日本大震災, Higashi nihon daishinsai) and is also known as the 2011 Tōhoku earthquake, the Great Sendai Earthquake, the Great Tōhoku Earthquake, and the 3.11 earthquake.

It was the most powerful earthquake ever recorded in Japan, and the fourth most powerful earthquake in the world since modern record-keeping began in 1900.

The earthquake triggered powerful tsunami waves that may have reached heights of up to 40.5 metres (133 ft) in Miyako in Tōhoku's Iwate Prefecture, and which, in the Sendai area, traveled up to 10 km (6 mi) inland.The earthquake moved Honshu (the main island of Japan) 2.4 m (8 ft) east, shifted the Earth on its axis by estimates of between 10 cm (4 in) and 25 cm (10 in), increased earth's rotational speed by 1.8 µs per day, and generated infrasound waves detected in perturbations of the low-orbiting GOCE satellite.

Initially, the earthquake caused sinking of part of Honshu's Pacific coast by up to roughly a metre, but after about three years, the coast rose back and kept on rising to exceed its original height.The tsunami swept the Japanese mainland and killed over ten thousand people, mainly through drowning, though blunt trauma also caused many deaths. The latest report from the Japanese National Police Agency report confirms 15,897 deaths, 6,157 injured, and 2,533 people missing across twenty prefectures, and a report from 2015 indicated 228,863 people were still living away from their home in either temporary housing or due to permanent relocation.A report by the National Police Agency of Japan on 10 September 2018 listed 121,778 buildings as "total collapsed", with a further 280,926 buildings "half collapsed", and another 699,180 buildings "partially damaged". The earthquake and tsunami also caused extensive and severe structural damage in north-eastern Japan, including heavy damage to roads and railways as well as fires in many areas, and a dam collapse. Japanese Prime Minister Naoto Kan said, "In the 65 years after the end of World War II, this is the toughest and the most difficult crisis for Japan." Around 4.4 million households in northeastern Japan were left without electricity and 1.5 million without water.The tsunami caused nuclear accidents, primarily the level 7 meltdowns at three reactors in the Fukushima Daiichi Nuclear Power Plant complex, and the associated evacuation zones affecting hundreds of thousands of residents. Many electrical generators were taken down, and at least three nuclear reactors suffered explosions due to hydrogen gas that had built up within their outer containment buildings after cooling system failure resulting from the loss of electrical power. Residents within a 20 km (12 mi) radius of the Fukushima Daiichi Nuclear Power Plant and a 10 km (6.2 mi) radius of the Fukushima Daini Nuclear Power Plant were evacuated.

Early estimates placed insured losses from the earthquake alone at US$14.5 to $34.6 billion. The Bank of Japan offered ¥15 trillion (US$183 billion) to the banking system on 14 March in an effort to normalize market conditions. The World Bank's estimated economic cost was US$235 billion, making it the costliest natural disaster in history.

Fault (geology)

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 movement. Large faults within the Earth's crust result from the action of plate tectonic forces, with the largest forming the boundaries between the plates, such as subduction zones or transform faults. Energy release associated with rapid movement on active faults is the cause of most earthquakes.

A fault plane is the plane that represents the fracture surface of a fault. A fault trace or fault line is a place where the fault can be seen or mapped on the surface. A fault trace is also the line commonly plotted on geologic maps to represent a fault.Since faults do not usually consist of a single, clean fracture, geologists use the term fault zone when referring to the zone of complex deformation associated with the fault plane.

Great Hanshin earthquake

The Great Hanshin earthquake (阪神・淡路大震災, Hanshin Awaji daishinsai), or Kobe earthquake, occurred on January 17, 1995 at 05:46:53 JST (January 16 at 20:46:53 UTC) in the southern part of Hyōgo Prefecture, Japan, when combined with Osaka, known as Hanshin. It measured 6.9 on the moment magnitude scale and had a maximum intensity of 7 on the JMA Seismic Intensity Scale. The tremors lasted for approximately 20 seconds. The focus of the earthquake was located 17 km beneath its epicenter, on the northern end of Awaji Island, 20 km away from the center of the city of Kobe.

Up to 6,434 people lost their lives; about 4,600 of them were from Kobe. Among major cities, Kobe, with its population of 1.5 million, was the closest to the epicenter and hit by the strongest tremors. This was Japan's worst earthquake in the 20th century after the Great Kantō earthquake in 1923, which claimed more than 105,000 lives.

List of natural disasters by death toll

A natural disaster is a sudden event that causes widespread destruction, major collateral damage or loss of life, brought about by forces other than the acts of human beings. A natural disaster might be caused by earthquakes, flooding, volcanic eruption, landslide, hurricanes etc. In order to be classified as a disaster, it will have profound environmental effect and/or human loss and frequently incurs financial loss.

Lists of earthquakes

The following is a list of earthquake lists, and of top earthquakes by magnitude and fatalities.

Richter magnitude scale

The so-called Richter magnitude scale – more accurately, Richter's magnitude scale, or just Richter magnitude – for measuring the strength ("size") of earthquakes refers to the original "magnitude scale" developed by Charles F. Richter and presented in his landmark 1935 paper, and later revised and renamed the Local magnitude scale, denoted as "ML" or "ML". Because of various shortcomings of the ML scale most seismological authorities now use other scales, such as the moment magnitude scale (Mw ), to report earthquake magnitudes, but much of the news media still refers to these as "Richter" magnitudes. All magnitude scales retain the logarithmic character of the original, and are scaled to have roughly comparable numeric values.

San Andreas Fault

The San Andreas Fault is a continental transform fault that extends roughly 1,200 kilometers (750 mi) through California. It forms the tectonic boundary between the Pacific Plate and the North American Plate, and its motion is right-lateral strike-slip (horizontal). The fault divides into three segments, each with different characteristics and a different degree of earthquake risk. The slip rate along the fault ranges from 20 to 35 mm (0.79 to 1.38 in)/yr.The fault was identified in 1895 by Professor Andrew Lawson of UC Berkeley, who discovered the northern zone. It is often described as having been named after San Andreas Lake, a small body of water that was formed in a valley between the two plates. However, according to some of his reports from 1895 and 1908, Lawson actually named it after the surrounding San Andreas Valley. Following the 1906 San Francisco earthquake, Lawson concluded that the fault extended all the way into southern California.

In 1953, geologist Thomas Dibblee concluded that hundreds of miles of lateral movement could occur along the fault. A project called the San Andreas Fault Observatory at Depth (SAFOD) near Parkfield, Monterey County, was drilled through the fault during 2004 – 2007 to collect material and make physical and chemical observations to better understand fault behavior.

Seismology

Seismology ( ; from Ancient Greek σεισμός (seismós) meaning "earthquake" and -λογία (-logía) meaning "study of") is the scientific study of earthquakes and the propagation of elastic waves through the Earth or through other planet-like bodies. The field also includes studies of earthquake environmental effects such as tsunamis as well as diverse seismic sources such as volcanic, tectonic, oceanic, atmospheric, and artificial processes such as explosions. A related field that uses geology to infer information regarding past earthquakes is paleoseismology. A recording of earth motion as a function of time is called a seismogram. A seismologist is a scientist who does research in seismology.

Tsunami

A tsunami (from Japanese: 津波, "harbour wave";

English pronunciation: soo-NAH-mee or ) or tidal wave,, also known as a seismic sea wave, 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 other underwater explosions (including detonations, landslides, glacier calvings, meteorite impacts and other disturbances) above or below water all have the potential to generate a tsunami. Unlike normal ocean waves, which are generated by wind, or tides, which are generated by the gravitational pull of the Moon and the Sun, a tsunami is generated by the displacement of water.

Tsunami waves do not resemble normal undersea currents or sea waves because their wavelength is far longer. Rather than appearing as a breaking wave, a tsunami may instead initially resemble a rapidly rising tide. For this reason, it is often referred to as a "tidal wave", although this usage is not favoured by the scientific community because it might give the false impression of a causal relationship between tides and tsunamis. Tsunamis generally consist of a series of waves, with periods ranging from minutes to hours, arriving in a so-called "internal wave train". Wave heights of tens of metres can be generated by large events. Although the impact of tsunamis is limited to coastal areas, their destructive power can be enormous, and they can affect entire ocean basins. The 2004 Indian Ocean tsunami was among the deadliest natural disasters in human history, with at least 230,000 people killed or missing in 14 countries bordering the Indian Ocean.

The Ancient Greek historian Thucydides suggested in his 5th century BC History of the Peloponnesian War that tsunamis were related to submarine earthquakes, but the understanding of tsunamis remained slim until the 20th century and much remains unknown. Major areas of current research include determining why some large earthquakes do not generate tsunamis while other smaller ones do; accurately forecasting the passage of tsunamis across the oceans; and forecasting how tsunami waves interact with shorelines.

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