Global plate tectonic movement
An
earthquake (also known as a
quake,
tremor or
temblor) is the result of a sudden release of energy in the
Earth's crust that creates
seismic waves. The
seismicity or
seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. Earthquakes are measured using observations from
seismometers. The
moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The more numerous earthquakes smaller than magnitude 5 reported by national seismological observatories are measured mostly on the local magnitude scale, also referred to as the
Richter scale. These two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly almost imperceptible and magnitude 7 and over potentially cause serious damage over large areas, depending on their depth. The largest earthquakes in historic times have been of magnitude slightly over 9, although there is no limit to the possible magnitude. The most recent large earthquake of magnitude 9.0 or larger was a
9.0 magnitude earthquake in Japan in 2011 (as of March 2011), and it was the largest Japanese earthquake since records began. Intensity of shaking is measured on the modified
Mercalli scale. The shallower an earthquake, the more damage to structures it causes, all else being equal.
[1]
At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of 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.
Naturally occurring earthquakes
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 behaviour. Once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the
stored energy. This energy is released as a combination of radiated elastic
strain seismic waves, 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 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 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, 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.
This is so because the energy released in an earthquake, and thus its magnitude, is proportional to the area of the fault that ruptures
[3] 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 mantel, are the only parts of our planet which can store elastic energy and release it in fault ruptures. Rocks hotter than about 300 degrees Celcius flow in response to stress, they do not rupture in earthquakes.
[4][5] The maximum observed lengths of ruptures and mapped faults, which may break in one go are approximately 1000 km. 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.
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
[1]. Thus the width of the plane within the top brittle crust of the Earth can become 50 to 100 km (
Tohoku, 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 within the brittle crust
[2], thus earthquakes with magnitudes much large 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 6 km.
[6][3]
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.
[7] 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
Where plate boundaries occur within
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.
[8]
All tectonic plates have internal stress fields caused by their interactions with neighbouring plates and sedimentary loading or unloading (e.g. deglaciation
[9]). These stresses may be sufficient to cause failure along existing fault planes, giving rise to
intraplate earthquakes.
[10]
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, where older and colder
oceanic crust descends beneath another tectonic plate,
deep-focus earthquakes may occur at much greater depths (ranging from 300 up to 700 kilometers).
[11] 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.
[12]
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
Mount St. Helens eruption of 1980.
[13] 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.
[14]
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.
[15]
Rupture propagation is generally modelled 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 neighbouring coast, as in the
1896 Meiji-Sanriku earthquake.
[15]
Earthquake clusters
Most earthquakes form part of a sequence, related to each other in terms of location and time.
[16] 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.
[17]
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.
[16]
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.
[18]
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.
[19][20]
Size and 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.
[21][22] 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.
[23] 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.
[24] 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
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.
[26] In recent years, the number of major earthquakes per year has decreased, though this is probably a statistical fluctuation rather than a systematic trend. More detailed statistics on the size and frequency of earthquakes is available from the
United States Geological Survey (USGS).
[27] Alternatively, some scientists suggest that the recent increase in major earthquakes 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.
[28]
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.
[29][30] Massive earthquakes tend to occur along other plate boundaries, too, such as along the
Himalayan Mountains.
[31]
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.
[32]
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.
[33] 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.
[34] The greatest earthquake in Australia's history is also claimed to be induced by humanity, through coal mining.
The city of Newcastle 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.
[35]
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:
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.
[36] 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.
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 of earthquakes
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
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.
[37] 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.
[38]
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.
[39]
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.
[40]
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.
[41]
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.
[42]
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.
[42]
Floods
A flood is an overflow of any amount of water that reaches land.
[43] 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 collapse and cause floods.
[44]
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.
[45]
Tidal forces
Research work has shown a robust correlation between small tidally induced forces and non-volcanic tremor activity.
[46][47][48][49]
Human impacts
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, higher insurance premiums, Earthquakes can also cause volcanic eruptions, bringing further problems.
Major earthquakes
One of the most devastating earthquakes in recorded history occurred on 23 January 1556 in the
Shaanxi province, China, killing more than 830,000 people (see
1556 Shaanxi earthquake).
[50] Most of the population in the area at the time lived in
yaodongs, artificial caves in loess cliffs, many of which collapsed during the catastrophe with great loss of life. The
1976 Tangshan earthquake, with death toll estimated to be between 240,000 to 655,000, is believed to be the largest earthquake of the 20th century by death toll.
[51]
The largest earthquake that has been measured on a seismograph reached 9.5 magnitude, occurring on 22 May 1960.
[21][22] Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the
Good Friday Earthquake, which was centered in
Prince William Sound, Alaska.
[52][53] 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.
Preparation
To predict the likelihood of future seismic activity,
geologists and other scientists examine the rock of an area to determine if the rock appears "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.
[54] 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.
[54] 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.
[54]
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.),
[55] 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
[56] and the New Zealand Society for Earthquake Engineering (NZSEE)'s guidelines.
[57]
Studies about
earthquake precursors are important to try predict strong earthquakes.
History
An image from a 1557 book
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."
[58] 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.
[58] 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.
[58] Pliny the Elder called earthquakes "underground thunderstorms."
[58]
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 dripped on Loki's face, forcing him to jerk his head away and thrash against his bonds, which caused the earth to tremble.
[59]
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.
[60]
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.
[61] Fictional earthquakes tend to strike suddenly and without warning.
[61] 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).
[61] 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.
[61] 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.
[62] 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.
[63] 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.
[64][65] 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.
[66] 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.
[67]
See also
References
- ^ Earthquake FAQ
- ^ Spence, William; S. A. Sipkin, G. L. Choy (1989). "Measuring the Size of an Earthquake". United States Geological Survey. Retrieved 2006-11-03.
- ^ Wyss, M. 1979, “Estimating expectable maximum magnitude of earthquakes from fault dimensions” Geology, 7, 336-340.
- ^ 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
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