Earthquake

Global earthquake epicenters, 1963–1998

An earthquake is a sudden and sometimes catastrophic movement of a part of the Earth's surface. Earthquakes result from the dynamic release of elastic strain energy that radiates seismic waves. Earthquakes typically result from the movement of faults, planar zones of deformation within the Earth's upper crust. The word earthquake is also widely used to indicate the source region itself. The Earth's lithosphere is a patch work of plates in slow but constant motion (see plate tectonics). Earthquakes occur where the stress resulting from the differential motion of these plates exceeds the strength of the crust. The highest stress (and possible weakest zones) are most often found at the boundaries of the tectonic plates and hence these locations are where the majority of earthquakes occur. Events located at plate boundaries are called interplate earthquakes; the less frequent events that occur in the interior of the lithospheric plates are called intraplate earthquakes (see, for example, New Madrid Seismic Zone). Earthquakes related to plate tectonics are called tectonic earthquakes. Most earthquakes are tectonic, but they also occur in volcanic regions and as the result of a number of anthropogenic sources, such as reservoir induced seismicity, mining and the removal or injection of fluids into the crust. Seismic waves including some strong enough to be felt by humans can also be caused by explosions (chemical or nuclear), landslides, and collapse of old mine shafts, though these sources are not strictly earthquakes.

Characteristics

Large numbers of earthquakes occur on a daily basis on Earth, but the majority of them are detected only by seismometers and cause no damage .

Most earthquakes occur in narrow regions around plate boundaries down to depths of a few tens of kilometres where the crust is rigid enough to support the elastic strain. Where the crust is thicker and colder they will occur at greater depths and the opposite in areas that are hot. At subduction zones where plates descend into the mantle, earthquakes have been recorded to a depth of 600 km, although these deep earthquakes are caused by different mechanisms than the more common shallow events. Some deep earthquakes may be due to the transition of olivine to spinel, which is more stable in the deep mantle.

Large earthquakes can cause serious destruction and massive loss of life through a variety of agents of damage, including fault rupture, vibratory ground motion (i.e., shaking), inundation (e.g., tsunami, seiche, dam failure), various kinds of permanent ground failure (e.g. liquefaction, landslide), and fire or a release of hazardous materials. In a particular earthquake, any of these agents of damage can dominate, and historically each has caused major damage and great loss of life, but for most of the earthquakes shaking is the dominant and most widespread cause of damage. There are four types of seismic waves that are all generated simultaneously and can be felt on the ground. S-waves (secondary or shear waves) and the two types of surfaces waves (Love waves and Rayleigh waves) are responsible for the shaking hazard.

Damage from the 1906 San Francisco earthquake. Section of collapsed freeway after the 1989 Loma Prieta earthquake.

Most large earthquakes are accompanied by other, smaller ones, that can occur either before or after the principal quake — these are known as foreshocks or aftershocks, respectively. While almost all earthquakes have aftershocks, foreshocks are far less common occurring in only about 10% of events. The power of an earthquake is distributed over a significant area, but in the case of large earthquakes, it can spread over the entire planet. Ground motions caused by very distant earthquakes are called teleseisms. The Rayleigh waves from the Sumatra-Andaman Earthquake of 2004 caused ground motion of over 1 cm even at the seismometers that were located far from it, although this displacement was abnormally large. Using such ground motion records from around the world it is possible to identify a point from which the earthquake's seismic waves appear to originate. That point is called its "focus" or "hypocenter" and usually proves to be the point at which the fault slip was initiated. The location on the surface directly above the hypocenter is known as the "epicenter". The total size of the fault that slips, the rupture zone, can be as large as 1000 km, for the biggest earthquakes. Just as a large loudspeaker can produce a greater volume of sound than a smaller one, large faults are capable of higher magnitude earthquakes than smaller faults are.

Earthquakes that occur below sea level and have large vertical displacements can give rise to tsunamis, either as a direct result of the deformation of the sea bed due to the earthquake or as a result of submarine landslips or "slides" directly or indirectly triggered by it.

Earthquake Size

The first method of quantifying earthquakes was intensity scales. In the United States the Mercalli (or Modified Mercalli, MM) scale is commonly used, while Japan (shindo) and the EU (European Macroseismic Scale) each have their own scales. These assign a numeric value (different for each scale) to a location based on the size of the shaking experienced there. The value 6 (normally denoted "VI") in the MM scale for example is:

Everyone feels movement. People have trouble walking. Objects fall from shelves. Pictures fall off walls. Furniture moves. Plaster in walls might crack. Trees and bushes shake. Damage is slight in poorly built buildings. No structural damage.

A Shakemap recorded by the Pacific Northwest Seismograph Network that shows the instrument recorded intensity of the shaking of the Nisqually earthquake on February 28, 2001. A Community Internet Intensity Map generated by the USGS that shows the intensity felt by humans by ZIP Code of the shaking of the Nisqually earthquake on February 28, 2001.

The problem with these scales is the measurement is subjective, often based on the worst damage in an area and influenced by local effects like site conditions that make it a poor measure for the relative size of different events in different places. For some tasks related to engineering and local planning it is still useful for the very same reasons and thus still collected. If you feel an earthquake in the US you can report the effects to the USGS.

The first attempt to qualitatively define one value to describe the size of earthquakes was the magnitude scale (the name being taking from similar formed scales used on the brightness of stars). In the 1930s, a California seismologist named Charles F. Richter devised a simple numerical scale (which he called the magnitude) to describe the relative sizes of earthquakes in Southern California. This is known as the “Richter scale”, “Richter Magnitude” or “Local Magnitude” (ML). It is obtained by measuring the maximum amplitude of a recording on a Wood-Anderson torsion seismometer (or one calibrated to it) at a distance of 600km from the earthquake. Other more recent Magnitude measurements include: body wave magnitude (mb), surface wave magnitude (Ms) and duration magnitude (MD). Each of these is scaled to gives values similar to the values given by the Richter scale. However as each is also based on the measurement of one part of the seismogram they do not measure the overall power of the source and can suffer from saturation at higher magnitude values (larger events fail to produce higher magnitude values).These scales are also empirical and as such there is no physical meaning to the values. They are still useful however as they can be rapidly calculated, there are catalogues of them dating back many years and are they are familiar to the public. Seismologists now favor a measure called the seismic moment, related to the concept of moment in physics, to measure the size of a seismic source. The seismic moment is calculated from seismograms but can also by obtained from geologic estimates of the size of the fault rupture and the displacement. The values of moments for different earthquakes ranges over several order of magnitude. As a result the moment magnitude (MW) scale was introduced by Hiroo Kanamori, which is comparable to the other magnitude scales but will not saturate at higher values.

Larger earthquakes occur less frequently than smaller earthquakes, the relationship being exponential, ie roughly ten times as many earthquakes larger than 4 occur in a particular time period than earthquakes larger than magnitude 5. For example it has been calculated that the average recurrence for the United Kingdom can be described as follows:

  • an earthquake of 3.7 or larger every 1 year
  • an earthquake of 4.7 or larger every 10 years
  • an earthquake of 5.6 or larger every 100 years.

Causes

Most earthquakes are powered by the release of the elastic strain that accumulate over time, typically, at the boundaries of the plates that make up the Earth's lithosphere via a process called Elastic-rebound theory. The Earth is made up of tectonic plates driven by the heat in the Earth's mantle and core. Where these plates meet stress accumulates. Eventually when enough stress accumulates, the plates move, causing an earthquake. Deep focus earthquakes, at depths of 100's km, are possibly generated as subducted lithospheric material catastrophically undergoes a phase transition since at the pressures and temperatures present at such depth elastic strain cannot be supported. Some earthquakes are also caused by the movement of magma in volcanoes, and such quakes can be an early warning of volcanic eruptions. A rare few earthquakes have been associated with the build-up of large masses of water behind dams, such as the Kariba Dam in Zambia, Africa, and with the injection or extraction of fluids into the Earth's crust (e.g. at certain geothermal power plants and at the Rocky Mountain Arsenal). Such earthquakes occur because the strength of the Earth's crust can be modified by fluid pressure. Earthquakes have also been known to be caused by the removal of natural gas from subsurface deposits, for instance in the northern Netherlands. Finally, ground shaking can also result from the detonation of explosives. Thus scientists have been able to monitor, using the tools of seismology, nuclear weapons tests performed by governments that were not disclosing information about these tests along normal channels. Earthquakes such as these, that are caused by human activity, are referred to by the term induced seismicity.


Another type of movement of the Earth is observed by terrestrial spectroscopy. These oscillations of the earth are either due to the deformation of the Earth by tide caused by the Moon or the Sun, or other phenomena.

A recently proposed theory suggests that some earthquakes may occur in a sort of earthquake storm, where one earthquake will trigger a series of earthquakes each triggered by the previous shifts on the fault lines, similar to aftershocks, but occurring years later.

Preparation for earthquakes

  • Emergency preparedness
  • Household seismic safety
  • Seismic retrofit
  • Earthquake prediction

Specific fault articles

  • Alpine Fault
  • Calaveras Fault
  • Hayward Fault Zone
  • North Anatolian Fault Zone
  • New Madrid Fault Zone
  • San Andreas Fault

Specific earthquake articles

  • Shaanxi Earthquake (1556). Deadliest known earthquake in history, estimated to have killed 830,000 in China.
  • Cascadia Earthquake (1700).
  • Kamchatka earthquakes (1737 and 1952).
  • Lisbon earthquake (1755).
  • New Madrid Earthquake (1811).
  • Fort Tejon Earthquake (1857).
  • Charleston earthquake (1886). Largest earthquake in the Southeast and killed 100.
  • San Francisco Earthquake (1906).
  • Great Kanto earthquake (1923). On the Japanese island of Honshu, killing over 140,000 in Tokyo and environs.
  • Kamchatka earthquakes (1952 and 1737).
  • Great Chilean Earthquake (1960). Biggest earthquake ever recorded, 9.5 on Moment magnitude scale.
  • Good Friday Earthquake (1964) Alaskan earthquake.
  • Ancash earthquake (1970). Caused a landslide that buried the town of Yungay, Peru; killed over 40,000 people.
  • Sylmar earthquake (1971). Caused great and unexpected destruction of freeway bridges and flyways in the San Fernando Valley, leading to the first major seismic retrofits of these types of structures, but not at a sufficient pace to avoid the next California freeway collapse in 1989.
  • Tangshan earthquake (1976). The most destructive earthquake of modern times. The official death toll was 255,000, but many experts believe that two or three times that number died.
  • Great Mexican Earthquake (1985). 8.1 on the Richter Scale, killed over 6,500 people (though it is believed as many as 30,000 may have died, due to missing people never reappearing.)
  • Whittier Narrows earthquake (1987).
  • Armenian earthquake (1988). Killed over 25,000.
  • Loma Prieta earthquake (1989). Severely affecting Santa Cruz, San Francisco and Oakland in California. Revealed necessity of accelerated seismic retrofit of road and bridge structures.
  • Northridge, California earthquake (1994). Damage showed seismic resistance deficiencies in modern low-rise apartment construction.
  • Great Hanshin earthquake (1995). Killed over 6,400 people in and around Kobe, Japan.
  • İzmit earthquake (1999) Killed over 17,000 in northwestern Turkey.
  • Düzce earthquake (1999)
  • Chi-Chi earthquake (1999).
  • Nisqually Earthquake (2001).
  • Gujarat Earthquake (2001).
  • Dudley Earthquake (2002).
  • Bam Earthquake (2003).
  • Parkfield, California earthquake (2004). Not large (6.0), but the most anticipated and intensely instrumented earthquake ever recorded and likely to offer insights into predicting future earthquakes elsewhere on similar slip-strike fault structures.
  • Chuetsu Earthquake (2004).
  • Indian Ocean Earthquake (2004). One of the largest earthquakes ever recorded at 9.0. Epicenter off the coast of the Indonesian island Sumatra. Triggered a tsunami which caused nearly 300,000 deaths spanning several countries.
  • Sumatran Earthquake (2005).
  • Fukuoka earthquake (2005).
  • Kashmir earthquake (2005). Killed over 79,000 people. Many more at risk from the Kashmiri winter.
  • Lake Tanganyika earthquake (2005).



This page about earthquake includes information from a Wikipedia article.
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. Nevertheless, the form "daylight savings time" appears without remark as to its nonstandardness in some dictionaries, including The American Heritage Dictionary. A recently proposed theory suggests that some earthquakes may occur in a sort of earthquake storm, where one earthquake will trigger a series of earthquakes each triggered by the previous shifts on the fault lines, similar to aftershocks, but occurring years later. Most compound adjectives are joined with a hyphen, but "daylight-saving time," too, is nonstandard. These oscillations of the earth are either due to the deformation of the Earth by tide caused by the Moon or the Sun, or other phenomena. In the standard form of the name, "daylight saving" is a compound adjective (part of which is a participle) that modifies "time." A common variant is daylight savings time. Although this alternate form is frequently heard in speech, it is nonstandard and appears rarely in edited writing.
Another type of movement of the Earth is observed by terrestrial spectroscopy. This is especially important in autumn, just before the heating season causes an increase in home fires.

Earthquakes such as these, that are caused by human activity, are referred to by the term induced seismicity. For example, the Country Fire Authority of Victoria in Australia has been running a program called "Change Your Clock, Change Your Smoke Alarm Battery" for several years. Thus scientists have been able to monitor, using the tools of seismology, nuclear weapons tests performed by governments that were not disclosing information about these tests along normal channels. Fire safety officials in Australia, Canada, New Zealand, and the United States encourage citizens to use the two annual time changes as a reminder to check the batteries in home and office fire alarms and smoke detectors. Finally, ground shaking can also result from the detonation of explosives. Another common mnemonic of equal meaning is "spring ahead, fall behind.". Earthquakes have also been known to be caused by the removal of natural gas from subsurface deposits, for instance in the northern Netherlands. This uses the word "fall" to mean "autumn"; while this usage has died out in British English, it is still very common in North American English.

Such earthquakes occur because the strength of the Earth's crust can be modified by fluid pressure. The mnemonic "spring forward, fall back" tells us how to reset clocks when the time changes, regardless of hemisphere (although it has to be remembered that spring and autumn occur during different months in the northern and southern hemispheres). at certain geothermal power plants and at the Rocky Mountain Arsenal). Different people start their day at different times (office workers start their day later than factory workers, who start their day later than farm workers), regardless of daylight saving time. A rare few earthquakes have been associated with the build-up of large masses of water behind dams, such as the Kariba Dam in Zambia, Africa, and with the injection or extraction of fluids into the Earth's crust (e.g. Other critics suggest that DST is, at its heart, government paternalism and that people rise in the morning as a matter of choice because many people enjoy nighttime hours and their jobs do not require them to make the most of daylight. Some earthquakes are also caused by the movement of magma in volcanoes, and such quakes can be an early warning of volcanic eruptions. DST is particularly unpopular among people working in agriculture because the animals do not observe it, and thus the people are placed out of synchronization with the rest of the community, including school times, broadcast schedules, and the like.

Deep focus earthquakes, at depths of 100's km, are possibly generated as subducted lithospheric material catastrophically undergoes a phase transition since at the pressures and temperatures present at such depth elastic strain cannot be supported. Opponents point to the longer hours of darkness on winter mornings, especially in Scotland, the north of England and Northern Ireland which might well cause an increase in road accidents. Eventually when enough stress accumulates, the plates move, causing an earthquake. This would make winter evenings longer, thereby reducing traffic accidents and cases of seasonal affective disorder. Where these plates meet stress accumulates. Alternatively, some would like Britain to adopt Central European Time and jump forward another hour during the summer (adopting a Single/Double Summer Time from Britain's perspective). The Earth is made up of tectonic plates driven by the heat in the Earth's mantle and core. Some campaigners in Britain would like the country to stay on British Summer Time (BST) all year round, or in other words, adopt Central European Time and abolish BST.

Most earthquakes are powered by the release of the elastic strain that accumulate over time, typically, at the boundaries of the plates that make up the Earth's lithosphere via a process called Elastic-rebound theory. Some studies do show that changing the clock increases the traffic accident rate.[1] Following the spring shift to daylight saving time (when one hour of sleep is lost) there is a measurable increase in the number of traffic accidents that result in fatalities. For example it has been calculated that the average recurrence for the United Kingdom can be described as follows:. For example, during a North American time change, an autumn night where clocks are reset from 3 AM summer to 2 AM winter time, times between 2AM and 3AM will occur twice, causing confusion in transport schedules, payment systems, etc. Larger earthquakes occur less frequently than smaller earthquakes, the relationship being exponential, ie roughly ten times as many earthquakes larger than 4 occur in a particular time period than earthquakes larger than magnitude 5. No formal studies have been performed, but an enormous amount of time has been spent by software developers to deal with the fact that 2400 hours past 2pm is not necessarily 2pm 100 days later. As a result the moment magnitude (MW) scale was introduced by Hiroo Kanamori, which is comparable to the other magnitude scales but will not saturate at higher values. It is also speculated that one of the benefits—more afternoon sun—would also actually increase energy consumption as people get into their cars to enjoy more time for shopping and the like.

The values of moments for different earthquakes ranges over several order of magnitude. It was for this reason that Arizona rejected DST and opted to stay on standard time all year. The seismic moment is calculated from seismograms but can also by obtained from geologic estimates of the size of the fault rupture and the displacement. Air conditioning often uses more energy than artificial lighting. Seismologists now favor a measure called the seismic moment, related to the concept of moment in physics, to measure the size of a seismic source. When air conditioning was not widely available, the change did save energy; however, air conditioning is much more widespread now than it was several decades ago. They are still useful however as they can be rapidly calculated, there are catalogues of them dating back many years and are they are familiar to the public. While many people use more sunlight under DST, most people also experience more heat, which prompts many people to turn on the air conditioner during the warmer afternoon hours.

However as each is also based on the measurement of one part of the seismogram they do not measure the overall power of the source and can suffer from saturation at higher magnitude values (larger events fail to produce higher magnitude values).These scales are also empirical and as such there is no physical meaning to the values. There is also a question whether the decrease in lighting costs justifies the increase in summertime air conditioning costs. Each of these is scaled to gives values similar to the values given by the Richter scale. It is also noted that much effort is spent reminding everyone twice a year of the change, and thousands are inconvenienced by showing up at the wrong time when they forget. Other more recent Magnitude measurements include: body wave magnitude (mb), surface wave magnitude (Ms) and duration magnitude (MD). The disruption in sleep patterns associated with setting clocks either forward or backward correlates with a spike in the number of severe auto accidents, as well as lost productivity as sleep-disrupted workers adjust to the schedule change. It is obtained by measuring the maximum amplitude of a recording on a Wood-Anderson torsion seismometer (or one calibrated to it) at a distance of 600km from the earthquake. Opponents claim that there is not enough benefit to justify the need to adjust clocks twice every year.

This is known as the “Richter scale”, “Richter Magnitude” or “Local Magnitude” (ML). DST is not universally accepted; many localities do not observe it. Richter devised a simple numerical scale (which he called the magnitude) to describe the relative sizes of earthquakes in Southern California. (Stats from this article). In the 1930s, a California seismologist named Charles F. $28 million in traffic costs. The first attempt to qualitatively define one value to describe the size of earthquakes was the magnitude scale (the name being taking from similar formed scales used on the brightness of stars). went on extended DST in 1974 and 1975 in response to the 1973 energy crisis, Department of Transportation studies found that observing DST in March and April saved 10,000 barrels of oil a day, and prevented about 2,000 traffic injuries and 50 fatalities saving about U.S.

If you feel an earthquake in the US you can report the effects to the USGS. When the U.S. For some tasks related to engineering and local planning it is still useful for the very same reasons and thus still collected. Other benefits cited include prevention of traffic injuries (by allowing more people to return home from work or school in daylight), and crime reduction (by reducing people's risk of being targets of crimes that are more common in dark areas). The problem with these scales is the measurement is subjective, often based on the worst damage in an area and influenced by local effects like site conditions that make it a poor measure for the relative size of different events in different places. Most people plan outdoor activities during the increased hours of sunlight. No structural damage. Another perceived benefit of DST is increased opportunities for outdoor activities.

Damage is slight in poorly built buildings. During the summer most people would wake up after the sun rises, regardless of whether daylight saving time is in effect or not, so there is no increased need for morning lighting to offset the afternoon drop in energy usage. Trees and bushes shake. Part of the reason that it is normally observed in the late spring, summer, and early autumn is because during the winter months the amount of energy saved by moving sunset one hour later is negated by the increased need for morning lighting by moving sunrise by the same amount. Plaster in walls might crack. United States Department of Transportation studies showed that DST reduces the country's electricity usage by one percent while DST is in effect. Furniture moves. Because people tend to observe the same bedtime year-round, by artificially moving sunset one hour later, the amount of energy used is theoretically reduced.

Pictures fall off walls. Theoretically, the amount of residential electricity needed in the evening hours is dependent both on when the sun sets and when people go to bed. Objects fall from shelves. One of the major reasons given for observing DST is energy conservation. People have trouble walking. Starting and ending dates are variable: normally, Brazilian DST starts at 00:00 on an October (rarely November) Sunday and ends at 00:00 on a February Sunday. Everyone feels movement. Brazil adopted DST for the first time in 1931, but uninterruptedly since 1985 in southern states (south, southeast regions and states of Goiás and Mato Grosso do Sul).

The value 6 (normally denoted "VI") in the MM scale for example is:. In specific years the starting and ending dates have been modified for political or climatic reasons. These assign a numeric value (different for each scale) to a location based on the size of the shaking experienced there. The current law which affects the entire country was enacted in 1970, but it had observed the practice as early as 1927 when the country had been divided into two distinct time zones. In the United States the Mercalli (or Modified Mercalli, MM) scale is commonly used, while Japan (shindo) and the EU (European Macroseismic Scale) each have their own scales. Chile switches to DST at 24:00 on the second Saturday in October and reverts to Local Standard Time (LST) at 24:00 on the second Sunday the following March. The first method of quantifying earthquakes was intensity scales. Standard Time Zone Boundary in the State of Indiana (a 139 KB pdf file) has some history, public comments from each county, the final DOT determination, and the resulting time zone boundary.

Earthquakes that occur below sea level and have large vertical displacements can give rise to tsunamis, either as a direct result of the deformation of the sea bed due to the earthquake or as a result of submarine landslips or "slides" directly or indirectly triggered by it. Currently, Pulaski and Martin counties are reconsidering their bid to join the Central time zone. Just as a large loudspeaker can produce a greater volume of sound than a smaller one, large faults are capable of higher magnitude earthquakes than smaller faults are. These counties are: Starke and Pulaski Counties in the Northwest, and Daviess, Dubois, Knox, Martin, Perry, and Pike in the Southwest. The total size of the fault that slips, the rupture zone, can be as large as 1000 km, for the biggest earthquakes. As a result of the review, the United States Department of Transportation moved eight more counties to the Central time zone, effective when DST begins on April 2, 2006. The location on the surface directly above the hypocenter is known as the "epicenter". The bill to observe DST also required the governor to request federal review of the time zone divisions in the state.

That point is called its "focus" or "hypocenter" and usually proves to be the point at which the fault slip was initiated. On April 29, 2005, the Indiana legislature voted to begin observing daylight saving time statewide in 2006. Using such ground motion records from around the world it is possible to identify a point from which the earthquake's seismic waves appear to originate. From 1991 until April 1, 2006 the state had three kinds of time zones and DST observances:. The Rayleigh waves from the Sumatra-Andaman Earthquake of 2004 caused ground motion of over 1 cm even at the seismometers that were located far from it, although this displacement was abnormally large. Opponents claimed that daylight saving time created costs and inconvenience associated with changing clocks twice a year and had little or no real value. Ground motions caused by very distant earthquakes are called teleseisms. Some supporters claimed that some businesses had located out-of-state due to the time-related confusion.

The power of an earthquake is distributed over a significant area, but in the case of large earthquakes, it can spread over the entire planet. Being out of sync with neighboring states and the national changing of clocks, supporters argued, had a negative economic impact on the state. While almost all earthquakes have aftershocks, foreshocks are far less common occurring in only about 10% of events. In the past, neighboring communities sometimes ended up one or even two hours apart. Most large earthquakes are accompanied by other, smaller ones, that can occur either before or after the principal quake — these are known as foreshocks or aftershocks, respectively. DST has been a long-standing controversy in Indiana, not only as an agricultural state, but also because the border separating the Eastern and Central time zones divides the state. S-waves (secondary or shear waves) and the two types of surfaces waves (Love waves and Rayleigh waves) are responsible for the shaking hazard. Hawaii does not observe DST.

There are four types of seismic waves that are all generated simultaneously and can be felt on the ground. However, the large Navajo Indian Reservation within it does. In a particular earthquake, any of these agents of damage can dominate, and historically each has caused major damage and great loss of life, but for most of the earthquakes shaking is the dominant and most widespread cause of damage. Most of Arizona does not observe DST. liquefaction, landslide), and fire or a release of hazardous materials. Certain types of information systems (those that schedule future events with reference to UTC, for example) are almost guaranteed to encounter serious desynchronization problems unless both computers and databases are carefully updated—in some cases by hand. Large earthquakes can cause serious destruction and massive loss of life through a variety of agents of damage, including fault rupture, vibratory ground motion (i.e., shaking), inundation (e.g., tsunami, seiche, dam failure), various kinds of permanent ground failure (e.g. More difficult to quantify is the amount of labor and money that may be spent correcting errors that arise due to a failure to update computers.

Some deep earthquakes may be due to the transition of olivine to spinel, which is more stable in the deep mantle. A two-minute procedure for updating a computer, multiplied by a hundred million computers, represents nearly 1700 years of full-time labor. At subduction zones where plates descend into the mantle, earthquakes have been recorded to a depth of 600 km, although these deep earthquakes are caused by different mechanisms than the more common shallow events. In order to change the dates and times at which the automatic jump to or from DST occurs, these tables must be modified, which requires some sort of manual intervention by a human being in the great majority of cases. Where the crust is thicker and colder they will occur at greater depths and the opposite in areas that are hot. Most computers are programmed to adjust automatically for DST, but they do so based on static tables stored directly on the computer itself. Most earthquakes occur in narrow regions around plate boundaries down to depths of a few tens of kilometres where the crust is rigid enough to support the elastic strain. An additional issue raised by this extension is that it requires reconfiguration of virtually every computer in the United States.

Large numbers of earthquakes occur on a daily basis on Earth, but the majority of them are detected only by seismometers and cause no damage . The extension was greeted by criticism from the airline industry and those concerned for the safety of children traveling to school in the dark before the late sunrise. . (See this article, for example.). Seismic waves including some strong enough to be felt by humans can also be caused by explosions (chemical or nuclear), landslides, and collapse of old mine shafts, though these sources are not strictly earthquakes. There is very little recent research on what the actual positive effects, if any, might be. Most earthquakes are tectonic, but they also occur in volcanic regions and as the result of a number of anthropogenic sources, such as reservoir induced seismicity, mining and the removal or injection of fluids into the crust. Department of Energy information from the 1970s, the accuracy and relevance of which the DoE no longer stands by.

Earthquakes related to plate tectonics are called tectonic earthquakes. Proponents claimed that the extension would save "the equivalent of" 10,000 barrels of oil per day, but this figure was based on U.S. Events located at plate boundaries are called interplate earthquakes; the less frequent events that occur in the interior of the lithospheric plates are called intraplate earthquakes (see, for example, New Madrid Seismic Zone). The change was introduced by the Energy Policy Act of 2005; the House had originally approved a motion that would have extended DST even further. The highest stress (and possible weakest zones) are most often found at the boundaries of the tectonic plates and hence these locations are where the majority of earthquakes occur. Starting March 11, 2007, daylight saving time will be extended another four to five weeks, from the second Sunday of March to the first Sunday of November. Earthquakes occur where the stress resulting from the differential motion of these plates exceeds the strength of the crust. In response to the 1973 energy crisis, daylight saving in the United States was begun earlier in both 1974 and 1975, commencing on the first Sunday in January (January 6) in the former year and the last Sunday in February (February 23) in the latter.

The Earth's lithosphere is a patch work of plates in slow but constant motion (see plate tectonics). The law was amended again in 1986 to begin daylight saving time on the first Sunday in April, to take effect the following year. The word earthquake is also widely used to indicate the source region itself. The law was amended in 1972 to permit states that straddle a time zone boundary to exempt the entire area of the state lying in one time zone. Earthquakes typically result from the movement of faults, planar zones of deformation within the Earth's upper crust. Any state that wanted to be exempt from daylight saving time could do so by passing a state law, provided that it exempt the entire state. Earthquakes result from the dynamic release of elastic strain energy that radiates seismic waves. federal Uniform Time Act of 1966 mandated that daylight saving time begin nationwide on the last Sunday of April and end on the last Sunday of October.

An earthquake is a sudden and sometimes catastrophic movement of a part of the Earth's surface. The U.S. Lake Tanganyika earthquake (2005). This resulted in a patchwork where some areas observed DST while adjacent areas did not, and it was not unheard of to have to reset one's clock several times during a relatively short trip (e.g., bus drivers operating between Moundsville, West Virginia, and Steubenville, Ohio had to reset their watches seven times over 35 miles). Many more at risk from the Kashmiri winter. States and localities were free to observe daylight saving time or not. Killed over 79,000 people. federal law did not address daylight saving time.

Kashmir earthquake (2005). From 1945 to 1966, U.S. Fukuoka earthquake (2005). This remained in effect until World War II began winding down and the requirement was removed on September 30, 1945. Sumatran Earthquake (2005). Daylight saving time was reinstated in the United States on February 9, 1942, again as a wartime measure to conserve resources. Triggered a tsunami which caused nearly 300,000 deaths spanning several countries. Beginning in 2007, it will start DST on the second Sunday in March, and change back to standard time on the first Sunday in November.

Epicenter off the coast of the Indonesian island Sumatra. Through the end of 2006, the United States starts its DST on the first Sunday in April, and changes back to standard time on the last Sunday in October. One of the largest earthquakes ever recorded at 9.0. state of Arizona, which also does not observe DST. Indian Ocean Earthquake (2004). The Mexican state of Sonora does not observe DST because it borders on the U.S. Chuetsu Earthquake (2004). Mexico has adopted DST nationwide, even in its tropical regions, because of its increasing economic ties to the United States.

Not large (6.0), but the most anticipated and intensely instrumented earthquake ever recorded and likely to offer insights into predicting future earthquakes elsewhere on similar slip-strike fault structures. Since April 2004, Cuba has remained on DST. Parkfield, California earthquake (2004). Cuba always starts its DST on April 1 but the end date varies. Bam Earthquake (2003). Saskatchewan Government Relations gives further details on Saskatchewan's time policies. Dudley Earthquake (2002). Lloydminster and its immediately surrounding region in Saskatchewan use the same timekeeping routine used by Alberta, DST with Mountain Standard Time.

Gujarat Earthquake (2001). The charter of the city of Lloydminster, which is bisected by the Saskatchewan–Alberta border, gives it a special exception (among areas in Saskatchewan) to use DST. Nisqually Earthquake (2001). Observationally, this is equivalent to the province being on Mountain Daylight Time year-round, though officially the province is considered to be part of the Central time zone. Chi-Chi earthquake (1999). (This policy was implemented when the Saskatchewan Time Act was passed in 1966, to solve the problems that arose when time zones varied from town to town.) Thus, in the summer months Saskatchewan is in sync with Mountain Daylight Time and in the winter months it is in sync with Central Standard Time. Düzce earthquake (1999). Saskatchewan is bisected by 105° west meridian, the central meridian of the Mountain Standard Time Zone (UTC−7), yet clocks are kept at UTC−6 all year long.

İzmit earthquake (1999) Killed over 17,000 in northwestern Turkey. The province of Saskatchewan is the largest part of that country that does not use DST, that is, it does not adjust clocks in spring and fall. Killed over 6,400 people in and around Kobe, Japan. The remaining provinces and territories will continue change time on the first Sunday of April and last Sunday of October unless they change their legislation. Great Hanshin earthquake (1995). In 2007, their DST will start on the second Sunday of March, and return to standard time on the first Sunday in November. Damage showed seismic resistance deficiencies in modern low-rise apartment construction. rules (The Calgary Sun).

Northridge, California earthquake (1994). The governments of Ontario, Manitoba, Quebec, and Alberta have pledged to change their daylight saving rules to match the new U.S. Revealed necessity of accelerated seismic retrofit of road and bridge structures. In Canada, time is under provincial and territorial jurisdiction, not federal. Severely affecting Santa Cruz, San Francisco and Oakland in California. Also, in 1988, they experimented with Double Daylight Time, when the clocks went ahead by two hours, instead of the usual one hour. Loma Prieta earthquake (1989). The Canadian province of Newfoundland and Labrador is an exception in that the time changes take place at 00:01 local standard time and 00:01 local daylight time respectively.

Killed over 25,000. In 2007, the starting and ending dates for DST will change in the United States and parts of Canada (see below). Armenian earthquake (1988). North America generally follows the same procedure, going by local time in each zone, each time zone switching at 02:00 LST (local standard time) to 03:00 LDT (local daylight time) on the first Sunday in April, and again from 02:00 LDT to 01:00 LST on the last Sunday in October. Whittier Narrows earthquake (1987). Polar or near-polar locations such as Iceland often opt out, as summer in these locations usually brings nearly uninterrupted daylight. 8.1 on the Richter Scale, killed over 6,500 people (though it is believed as many as 30,000 may have died, due to missing people never reappearing.). With Iceland observing UTC all year round, despite being at a longitude which would indicate UTC-1, the country may be said to be on continuous DST.

Great Mexican Earthquake (1985). Thus in Moscow (local time = UTC+3 in winter, UTC+4 in summer), daylight-saving time commences at 23:00 UTC on the day before the last Sunday in March, and ends at 23:00 UTC on the day before the last Sunday in October. The official death toll was 255,000, but many experts believe that two or three times that number died. In Russia, however, although the changeover dates are the same, clocks are moved forward or back at 02:00 winter time in all zones. The most destructive earthquake of modern times. (See also: European Summer Time). Tangshan earthquake (1976). from local times of 01:00/02:00/03:00 to 02:00/03:00/04:00 in March, and vice versa in October.

Caused great and unexpected destruction of freeway bridges and flyways in the San Fernando Valley, leading to the first major seismic retrofits of these types of structures, but not at a sufficient pace to avoid the next California freeway collapse in 1989. In the West European (UTC), Central European (UTC+1), and East European (UTC+2) time zones the change is simultaneous: on both dates the clocks are changed everywhere at 01:00 UTC, i.e. Sylmar earthquake (1971). All countries in Europe, except Iceland as noted below, observe daylight-saving time and change on the same date: moving clocks forward one hour on the last Sunday in March and back one hour on the last Sunday in October. Caused a landslide that buried the town of Yungay, Peru; killed over 40,000 people. The Department of Internal Affairs gives further historical information on their website. Ancash earthquake (1970). In New Zealand, daylight saving time begins at 2am (standard time) on the first Sunday in October each year, and ends at 2am (standard time) on the third Sunday of March.

Good Friday Earthquake (1964) Alaskan earthquake. See the Australian time zones article or this site for maps and further information on standard and daylight saving time in Australia. Biggest earthquake ever recorded, 9.5 on Moment magnitude scale. Queensland experimented with it for a year or two in the early 1970s, but it was not popular and was abandoned. Great Chilean Earthquake (1960). Western Australia, Northern Territory and Queensland do not have daylight saving. Kamchatka earthquakes (1952 and 1737). Tasmania starts DST earlier than the others, usually near the beginning of October.

On the Japanese island of Honshu, killing over 140,000 in Tokyo and environs. New South Wales, Victoria, Tasmania, Australian Capital Territory and South Australia apply daylight saving time. Great Kanto earthquake (1923). Some states/territories implement it and some do not. San Francisco Earthquake (1906). In Australia, daylight saving time is a state/territory-based initiative. Largest earthquake in the Southeast and killed 100. It has not used DST since then.

Charleston earthquake (1886). Pakistan experimented with DST in 2002 going from +5:00 to +6:00. Fort Tejon Earthquake (1857). For more on this subject, see Israeli Daylight Saving Law. New Madrid Earthquake (1811). Israel's Daylight Saving Time rules have changed repeatedly in recent years; there has been trouble reaching a consensus regarding Gregorian calendar end dates for DST as they are dependant on Jewish Holidays, which follow the lunar Hebrew calendar. Lisbon earthquake (1755). Israel adopts Daylight Saving Time on the last Friday before April 2 at 02:00, and returns to standard time at 02:00 of the Sunday of the month of Tishrei between Rosh Hashanah and Yom Kippur.

Kamchatka earthquakes (1737 and 1952). Thus, DST in Iran starts on the first day of Farvardin (around 21-22 March) and ends on the first day of Mehr (around 22 September). Cascadia Earthquake (1700). Iran uses the Persian calendar. Deadliest known earthquake in history, estimated to have killed 830,000 in China. India used DST briefly during its wars with Pakistan and China. Shaanxi Earthquake (1556). The PRC now uses one universal time zone for all of the nation from Urumqi in the northwest to Fujian in the southeast; the size of the nation was a major factor why DST was not considered practical in China.

San Andreas Fault. The People's Republic of China experimented with DST from 1986, but abandoned it in the 1990s. New Madrid Fault Zone. Egypt operates Daylight-Saving Time between the last Friday in April and the last Thursday in September when the clocks are 3 hours ahead of Greenwich Mean Time (GMT+3). North Anatolian Fault Zone. In the Southern Hemisphere, the beginning and ending dates are switched (thus the time difference between, e.g., the United Kingdom and Chile may be three, four, or five hours). Hayward Fault Zone. DST commonly begins in the Northern Hemisphere on either the first Sunday in April or the last Sunday in March, and ends on the last Sunday in October.

Calaveras Fault. With a few exceptions, switchovers between standard time and daylight saving time generally occur in the early morning hours of a Sunday morning, presumably because doing so then causes less disruption than a change on a weekday would. Alpine Fault. The dates of the beginning and ending of DST also vary by country. Earthquake prediction. The amount of the time shift varies, but one hour is the most common. Seismic retrofit. state in the tropics, does not observe DST.

Household seismic safety. Hawaii, the only U.S. Emergency preparedness. Daylight saving time is generally a temperate zone practice; day lengths in the tropics do not vary enough to justify DST. an earthquake of 5.6 or larger every 100 years. The law, however, proved so unpopular (mostly because people rose and went to bed earlier than in current times) that the law was later repealed. an earthquake of 4.7 or larger every 10 years. It was observed for seven months in 1918 and 1919.

an earthquake of 3.7 or larger every 1 year. Congress established several time zones (which were already in use by railroads and most cities since 1883) and made daylight saving time official (which went into effect on March 31) for the remainder of World War I. Then on March 19, 1918, the U.S. Shortly afterward, the United Kingdom followed suit, first adopting DST between May 21 and October 1, 1916. The idea of daylight saving time was first put into practice by the German government during the First World War between April 30 and October 1, 1916.

It was first seriously proposed by William Willett in the "Waste of Daylight", published in 1907, but he was unable to get the British government to adopt it despite considerable lobbying. (Read the full text.) However, the article was humorous; Franklin was not proposing DST, but rather that people should get up and go to bed earlier. It is sometimes asserted that DST was first proposed by Benjamin Franklin in a letter to the editors of the Journal of Paris. .

Note that the term commonly used in the United States, daylight savings time, is incorrect, for both historic (the correct name as provided by the act which inaugurated it in the United States is daylight saving time) and grammatical reasons. DST is most commonly used in temperate regions, due to the considerable variation in the amount of daylight versus darkness through the seasons in those regions. This is intended to provide a better match between the hours of daylight and the active hours of work and school. The official time is adjusted forward, (usually) one hour from its official standard time, remaining that way for the duration of the spring and summer months.

Daylight saving time (also called DST) is a term used for a system intended to "save" daylight (It is also known as summer time in both Britain and Europe). American Journal of Public Health 85, 92–95. (1995) Daylight saving time and motor vehicle crashes: the reduction in pedestrian and vehicle occupant fatalities. et al.

^  Ferguson, S.A. Their observance of DST was unofficial in this case, as a strict reading of the Uniform Time Act would not allow for this situation, but by observing DST, they remained synchronized with the greater Louisville and Cincinnati metropolitan areas. 2 counties near Cincinnati, Ohio and 3 counties near Louisville, Kentucky were on Eastern Standard time but did observe DST. 5 northwestern counties near Chicago, Illinois and 5 southwestern counties near Evansville, Indiana were on Central Standard Time and did use DST.

77 counties — most of the state — were on Eastern Standard Time but did not use DST.

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