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
refers to the frequency, type and size of earthquakes experienced over
a period of time. The word tremor is also used for non-earthquake
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.
1 Naturally occurring earthquakes
Earthquake fault types
1.2 Earthquakes away from plate boundaries
1.3 Shallow-focus and deep-focus earthquakes
1.4 Earthquakes and volcanic activity
1.5 Rupture dynamics
1.6 Tidal forces
2 Intensity of earth quaking and magnitude of earthquakes
3 Frequency of occurrence
4 Induced seismicity
5 Measuring and locating earthquakes
6 Effects of earthquakes
6.1 Shaking and ground rupture
6.2 Landslides and avalanches
6.7 Human impacts
7 Major earthquakes
11 Historical views
12 Recent studies
13 In culture
13.1 Mythology and religion
13.2 In popular culture
14 See also
17 External links
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 behavior. Once the fault has locked, continued
relative motion between the plates leads to increasing stress and
therefore, stored strain energy in the volume around the fault
surface. This continues until the stress has risen sufficiently to
break through the asperity, suddenly allowing sliding over the locked
portion of the fault, releasing the stored energy. This energy is
released as a combination of radiated elastic strain seismic waves,
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.
Earthquake fault types
Main article: Fault (geology)
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.
This is so because the energy released in an earthquake, and thus its
magnitude, is proportional to the area of the fault that ruptures
and the stress drop. Therefore, the 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 degrees Celsius flow in
response to stress; they do not rupture in earthquakes. The
maximum observed lengths of ruptures and mapped faults (which may
break in a single rupture) are approximately 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
San Andreas Fault (1857, 1906), the North Anatolian
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.
Aerial photo of the
San Andreas Fault
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. Thus the width of the plane
within the top brittle crust of the
Earth can become 50 to 100 km
(Japan, 2011; Alaska, 1964), making the most powerful earthquakes
Strike-slip faults tend to be oriented near vertically, resulting in
an approximate width of 10 km within the brittle crust, 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
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.
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
Main article: Intraplate earthquake
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
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
All tectonic plates have internal stress fields caused by their
interactions with neighboring plates and sedimentary loading or
unloading (e.g. deglaciation). These stresses may be sufficient to
cause failure along existing fault planes, giving rise to intraplate
Shallow-focus and deep-focus earthquakes
Main article: Depth of focus (tectonics)
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 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).
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.
Earthquakes and volcanic activity
Volcano tectonic earthquake
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.
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.
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
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
Tides may induce some seismicity, see tidal triggering of earthquakes
Most earthquakes form part of a sequence, related to each other in
terms of location and time. Most earthquake clusters consist of
small tremors that cause little to no damage, but there is a theory
that earthquakes can recur in a regular pattern.
Main article: Aftershock
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.
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. In August 2012, a swarm of earthquakes shook
Southern California's Imperial Valley, showing the most recorded
activity in the area since the 1970s.
Sometimes a series of earthquakes occur in what has been called an
earthquake storm, where the earthquakes strike a fault in clusters,
each triggered by the shaking or stress redistribution of the previous
earthquakes. Similar to 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
North Anatolian Fault in
Turkey in the 20th century and has been
inferred for older anomalous clusters of large earthquakes in the
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.
The first scale for measuring earthquake magnitudes was developed by
Charles F. Richter
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
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.
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. Minor earthquakes occur nearly constantly around the
world in places like
Alaska in the U.S., as well as in
El Salvador, Mexico, Guatemala, Chile, Peru, Indonesia, Iran,
Azores in Portugal, Turkey, New Zealand, Greece, Italy,
Nepal and Japan, but earthquakes can occur almost anywhere,
including Downstate New York, England, and Australia. 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. This is an example of the Gutenberg–Richter law.
The Messina earthquake and tsunami took as many as 200,000 lives on
December 28, 1908 in
Sicily and Calabria.
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.
United States Geological Survey
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. 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
United States Geological Survey (USGS). 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
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. Massive
earthquakes tend to occur along other plate boundaries, too, such as
along the Himalayan Mountains.
With the rapid growth of mega-cities such as
Tehran, in areas of high seismic risk, some seismologists are warning
that a single quake may claim the lives of up to 3 million
Main article: 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. Perhaps the best known example is the
2008 Sichuan earthquake
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. 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.
Measuring and locating earthquakes
Seismic scale and Seismology
The instrumental scales used to describe the size of an earthquake
began with the
Richter magnitude scale
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).
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
Every tremor produces different types of seismic waves, which travel
through rock with different velocities:
P-waves (shock- or pressure waves)
S-waves (both body waves)
Surface waves — (Rayleigh and Love waves)
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
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. 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
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.
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.
Effects of earthquakes
1755 copper engraving depicting
Lisbon in ruins and in flames after
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
Shaking and ground rupture
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. The ground-shaking is measured by ground
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
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.
Landslides and avalanches
Main article: Landslide
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.
Fires of the 1906 San Francisco earthquake
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.
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.
The tsunami of the 2004 Indian Ocean earthquake
Main article: Tsunami
Tsunamis are long-wavelength, long-period sea waves produced by the
sudden or abrupt movement of large volumes of water – including when
an earthquake occurs at sea. In the open ocean the distance between
wave crests can surpass 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
Tsunamis can also travel thousands of kilometers across open
ocean and wreak destruction on far shores hours after the earthquake
that generated them.
Ordinarily, subduction earthquakes under magnitude 7.5 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.
Main article: Flood
A flood is an overflow of any amount of water that reaches land.
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.
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
Ruins of the Għajn Ħadid Tower, which collapsed in an earthquake in
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, and higher insurance
Earthquakes (M6.0+) since 1900 through 2017
Earthquakes of magnitude 8.0 and greater since 1900. The apparent 3D
volumes of the bubbles are linearly proportional to their respective
Main article: Lists of earthquakes
One of the most devastating earthquakes in recorded history was the
Shaanxi earthquake, which occurred on 23 January 1556 in Shaanxi
province, China. More than 830,000 people died. 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.
The 1960 Chilean earthquake is the largest earthquake that has been
measured on a seismograph, reaching 9.5 magnitude on 22 May
1960. Its epicenter was near Cañete, Chile. The energy
released was approximately twice that of the next most powerful
Good Friday earthquake
Good Friday earthquake (March 27, 1964) which was
centered in Prince William Sound, Alaska. The ten largest
recorded earthquakes have all been megathrust earthquakes; however, of
these ten, only the
2004 Indian Ocean earthquake
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.
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. 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.
While forecasting is usually considered to be a type of prediction,
earthquake forecasting is often differentiated from earthquake
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. For well-understood faults the probability that a segment
may rupture during the next few decades can be estimated.
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
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
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.
An image from a 1557 book depicting an earthquake in
Italy in the 4th
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." 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. 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
Pliny the Elder
Pliny the Elder called earthquakes "underground
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.
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.
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.
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
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. Fictional earthquakes tend to strike suddenly
and without warning. For this reason, stories about earthquakes
generally begin with the disaster and focus on its immediate
aftermath, as in Short Walk to Daylight (1972), The Ragged Edge (1968)
Earthquake in New York (1999). A notable example is
Heinrich von Kleist's classic novella, The
Earthquake in Chile, which
describes the destruction of Santiago in 1647. Haruki Murakami's short
After the Quake
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
San Andreas Fault someday, as depicted
in the novels
Richter 10 (1996), Goodbye
California (1977), 2012
(2009) and San Andreas (2015) among other works. 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.
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.
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. 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. 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.
European-Mediterranean Seismological Centre
Lists of earthquakes
Quake (natural phenomenon)
Seismological Society of America
Types of earthquake
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Wikiquote has quotations related to: Earthquake
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Earthquake Hazards Program of the U.S. Geological Survey
Seismic Monitor – IRIS Consortium
Open Directory – Earthquakes
World earthquake map captures every rumble since 1898 —Mother Nature
Network (MNN) (29 June 2012)
Earthquake Response Training Tool: Protecting Yourself While
Responding to Earthquakes
CDC – NIOSH
Earthquake Cleanup and Response Resources
Icelandic Meteorological Office website Shows current seismic and
volcanic activity in Iceland. English available.
How Friction Evolves During an
Earthquake – Caltech
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