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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).

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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. The Spanish Aerocar, built in 1916 from a design by Spanish engineer Leonardo Torres y Quevedo, is a cable car which takes passengers over the whirlpool on the Canadian side, below the Falls. 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. The Maid of the Mist cruises, named for an ancient Ongiara Indian mythical character, have carried passengers into the whirlpools beneath the Falls since 1846. Another type of movement of the Earth is observed by terrestrial spectroscopy. Along the Niagara River, the Niagara River Recreational Trail runs the 56 km (35 miles) from Fort Erie to Fort George, and includes many historical sites from the War of 1812. Earthquakes such as these, that are caused by human activity, are referred to by the term induced seismicity. The observation deck of the nearby Skylon Tower offers the highest overhead view of the Falls, and in the opposite direction gives views as far as distant Toronto.6 With the Konica Minolta Tower, it is one of two towers in Canada with a view of the Falls.

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. On the Canadian side, Queen Victoria Park features manicured gardens, platforms offering spectacular views of both the American and Horseshoe Falls, and underground walkways leading into observation rooms which yield the illusion of being within the falling waters. Finally, ground shaking can also result from the detonation of explosives. The Niagara Scenic Trolley offers guided trips along the American Falls. Earthquakes have also been known to be caused by the removal of natural gas from subsurface deposits, for instance in the northern Netherlands. Nearby, the Cave of the Winds trail leads hikers down some three hundred steps to a point beneath Bridal Veil Falls. Such earthquakes occur because the strength of the Earth's crust can be modified by fluid pressure. From the American side, the American Falls can be viewed from walkways along Prospect Park, which also features an observation tower.

at certain geothermal power plants and at the Rocky Mountain Arsenal). From the Canadian side, floodlights illuminate both sides of the Falls for several hours after dark (until midnight). 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. Peak numbers of visitors occur in the summertime, when Niagara Falls are both a daytime and evening attraction. Some earthquakes are also caused by the movement of magma in volcanoes, and such quakes can be an early warning of volcanic eruptions. On August 4, 2005, professional golfer John Daly attempted to drive a golf ball over Niagara Falls, an approximate distance of 362 yards (331 m), falling just short in 20 attempts. 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. With the recent influx of more international tourists, annual visits exceeded 14 million in 2003.

Eventually when enough stress accumulates, the plates move, causing an earthquake. The Falls, or more particularly, the tourist-supported complex near the Falls, was the setting of the short-lived American television show Wonderfalls in early 2004. Where these plates meet stress accumulates. Much of the episode Return of the Technodrome in the 1987 Teenage Mutant Ninja Turtles cartoon series take place near the Niagara Falls and its hydroelectric plant. The Earth is made up of tectonic plates driven by the heat in the Earth's mantle and core. Later in the 20th century, the Falls was a featured location in 1980's movie Superman II, and was itself the subject of a popular IMAX movie. 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. Already a huge tourist attraction and favorite spot for honeymooners, Niagara Falls visits rose sharply in 1953 after the release of Niagara, a movie starring Marilyn Monroe.

For example it has been calculated that the average recurrence for the United Kingdom can be described as follows:. All survivors and stunters have passed over the Horseshoe Falls, where there are fewer boulders and the current can "throw" a person farther away from the brink and (hopefully) avoid the boulders. 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 human has ever survived a plunge over the American Falls, due to the many boulders and the relatively weak current. 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. While it is still not known whether Jones was determined to commit suicide, he survived the 16-story fall with only battered ribs, scrapes, and bruises. The values of moments for different earthquakes ranges over several order of magnitude. Kirk Jones became the first person to plunge over the Horseshoe Falls without a flotation device on October 20, 2003.

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. His survival, which no one thought possible, made news throughout the world. 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. Roger was plucked from the roiling plunge pool beneath the Horseshoe Falls after grabbing a life ring thrown to him by the crew of the Maid of the Mist boat. 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. In what some called the "Miracle at Niagara", Roger Woodward, a seven-year-old American boy, was swept over the Horseshoe Falls protected only by a life vest in July, 1960, as two tourists pulled his 17-year-old sister Deanne from the river at the lip of the American Falls. 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. Englishman Captain Matthew Webb, the first man to swim the English Channel, drowned in 1883 after unsuccessfully trying to swim across the whirlpools and rapids downriver from the Falls.

Each of these is scaled to gives values similar to the values given by the Richter scale. Their wires ran across the gorge, near the current Rainbow Bridge, not over the waterfall itself. Other more recent Magnitude measurements include: body wave magnitude (mb), surface wave magnitude (Ms) and duration magnitude (MD). Starting with the successful passage by Jean François "Blondin" Gravelet in 1859, tightrope walkers have drawn large crowds to their exploits. 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 daredevils have made crossing the Falls their goal. This is known as the “Richter scale”, “Richter Magnitude” or “Local Magnitude” (ML). Magician David Copperfield more recently added his name to the list of these daredevils, successfully travelling (or perhaps, appearing to travel) over the Falls in 1990.

Richter devised a simple numerical scale (which he called the magnitude) to describe the relative sizes of earthquakes in Southern California. Survivors of such stunts face charges and stiff fines, as it is illegal, on both sides of the border, to attempt to go over the Falls. In the 1930s, a California seismologist named Charles F. Some have survived unharmed, but others have drowned or been severely injured. 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). Since Taylor's historic ride, 14 other people have intentionally gone over the Falls in or on a device. If you feel an earthquake in the US you can report the effects to the USGS. In 1901, 63-year-old Annie Edson Taylor was the first person to go over the Falls in a barrel; she survived virtually unharmed.

For some tasks related to engineering and local planning it is still useful for the very same reasons and thus still collected. This began a long tradition of daredevils trying to go over the Falls and survive. 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. In October 1829, Sam Patch, who called himself The Yankee Leaper, jumped over the Horseshoe Falls and became the first known person to survive the plunge. No structural damage. It will be very difficult to solve the problem. Damage is slight in poorly built buildings. The result is that the viewing areas on the Canadian side are now often obscured by a layer of mist from the falls.

Trees and bushes shake. Students at the University of Guelph demonstrated, using scale models, that the air passes overtop of the new hotels, which causes a breeze to roll forward down the south sides of the buildings and spill down into the gorge under the falls, where it feeds into a whirlpool of moisture and air. Plaster in walls might crack. Recent construction of several tall buildings (most of them hotels) on the Canadian side of the falls has caused the airflow over the falls to change direction. Furniture moves. Even after this undertaking, Luna Island, the small piece of land between the main waterfall and the Bridal Veil, remained off limits to the public for years owing to fears that it was unstable and could collapse into the gorge at any time. Pictures fall off walls. A plan to remove the huge mound of talus deposited in 1954 was abandoned owing to cost, and in November 1969, the temporary dam was dynamited, restoring flow to the American Falls.

Objects fall from shelves. In June of that year, the Niagara River was completely diverted away from the American Falls for several months through the building of a temporary rock and earth dam (clearly visible in the photo at right), effectively shutting off the American Falls.5 While the Horseshoe Falls absorbed the extra flow, the US Army Corps of Engineers studied the riverbed and mechanically bolted faults which would otherwise have hastened the retreat of the American Falls. People have trouble walking. The most dramatic such work was performed in 1969. Everyone feels movement. In addition to the effects of diversion of water to the power stations, erosion control efforts have included underwater weirs to redirect the most damaging currents, and actual mechanical strengthening of the top of the Falls. The value 6 (normally denoted "VI") in the MM scale for example is:. In 1950, the two countries signed the Niagara River Water Diversion Treaty, which more specifically addressed the issue of water diversion.

These assign a numeric value (different for each scale) to a location based on the size of the shaking experienced there. On January 2, 1929 Canada and the United States reached an agreement on an action plan to preserve the Falls. 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. This process was slowed initially by diversion of increasing amounts of flow from the Niagara River into hydroelectric plants in both the United States and Canada. The first method of quantifying earthquakes was intensity scales. Until the modern era, the Falls were receding southward owing to erosion from two to ten feet (0.6 to 3.0 m) per year. 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. On the Canadian side, the Niagara Parks Commission governs land usage along the entire course of the Niagara River, from Lake Erie to Lake Ontario.

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. Both organizations have proved remarkably successful operations that have restricted development on both sides of the Falls and the Niagara River. The total size of the fault that slips, the rupture zone, can be as large as 1000 km, for the biggest earthquakes. In the same year, Ontario established the Queen Victoria Niagara Falls Park for the same purpose. The location on the surface directly above the hypocenter is known as the "epicenter". In 1885, New York state to begin to purchase land from developers, under the charter of the Niagara Reservation State Park. That point is called its "focus" or "hypocenter" and usually proves to be the point at which the fault slip was initiated. A series of Harrison's letters to newspapers in Boston and New York (collected in the 1882 pamphlet The Condition of Niagara Falls, and the Measures Needed to Preserve Them) were particularly influential in turning public opinion in favor of preservation [3].

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. Public dissatisfaction led to the Free Niagara movement, which included the artist Frederick Church, the landscape architect Frederick Law Olmsted, and the journalist Jonathan Baxter Harrison. 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. Development and commercial ventures threatened the natural beauty of the area, and visitors sometimes had to pay entrepreneurs a fee to view the Falls through holes in a fence. Ground motions caused by very distant earthquakes are called teleseisms. For the first two centuries after European settlement of the area, land on both sides of Niagara Falls was privately owned. 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. Nearby Niagara Falls International Airport and Buffalo Niagara International Airport were named after the waterfall, as were Niagara University, countless local businesses, and even one celestial body.4.

While almost all earthquakes have aftershocks, foreshocks are far less common occurring in only about 10% of events. The twin cities of Niagara Falls, Ontario and Niagara Falls, New York are connected by three bridges, including the Rainbow Bridge, just downriver from the Falls, which affords the closest view of the Falls, the Whirpool Bridge, and the newest bridge, the Lewiston-Queenston Bridge, located near the escarpment. 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. Since then the region has declined economically. S-waves (secondary or shear waves) and the two types of surfaces waves (Love waves and Rayleigh waves) are responsible for the shaking hazard. While the seaway diverted water traffic from nearby Buffalo and led to the demise of its steel and grain mills, other industries in the Niagara River valley flourished until the 1970s with the help of the electric power produced by the river. There are four types of seismic waves that are all generated simultaneously and can be felt on the ground. Ships can bypass Niagara Falls by means of the Welland Canal, which in the 1960s was improved and incorporated into the Saint Lawrence Seaway.

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. The project is expected to be completed in 2009, and will increase Sir Adam Beck's yearly output by about 1.6 TW·h. liquefaction, landslide), and fire or a release of hazardous materials. In August 2005, Ontario Power Generation, which is now responsible for the Sir Adam Beck stations, announced plans to build a new 10.4 km tunnel to tap water from farther up the Niagara river than is possible with the existing arrangement. 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. All together, Niagara's generating stations can produce about 4.4 GW of power. Some deep earthquakes may be due to the transition of olivine to spinel, which is more stable in the deep mantle. The most powerful hydroelectric stations on the Niagara River are Sir Adam Beck 1 and 2 on the Canadian side, and the Robert Moses Niagara Power Plant and the Lewiston Pump Generating Plant on the American side.

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. The water then passes through hydroelectric turbines that supply power to nearby areas of the United States and Canada before returning to the river well past the Falls. Where the crust is thicker and colder they will occur at greater depths and the opposite in areas that are hot. Currently between 50% and 75% of the Niagara River's flow is diverted via four huge tunnels that arise far upstream from the waterfalls. 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. The Government of Ontario eventually brought power transmission operations under public control in 1906, distributing Niagara's energy to various parts of that province. 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 . Private companies on the Canadian side also began to harness the energy of the Falls, employing both domestic and American firms in their efforts.

. Morgan, John Jacob Astor IV, and the Vanderbilts, they had constructed giant underground conduits leading to turbines generating upwards of 100,000 horsepower (75 MW), and were sending power as far as Buffalo, twenty miles (32 km) away. 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. By 1896, with financing from moguls like J.P. 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. In 1883, the Niagara Falls Power Company, a descendant of Schoellkopf's firm, hired George Westinghouse to design a system to generate alternating current. Earthquakes related to plate tectonics are called tectonic earthquakes. When Nikola Tesla, for whom a memorial was later built at Niagara Falls, invented the three-phase system of alternating current power transmission, distant transfer of electricity became possible.

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). In 1881, under the leadership of Jacob Schoellkopf, enough power was produced to send direct current to illuminate both the Falls themselves and nearby Niagara Falls village. 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. In 1853, the Niagara Falls Hydraulic Power and Mining Company was chartered, which eventually constructed the canals which would be used to generate electricity. Earthquakes occur where the stress resulting from the differential motion of these plates exceeds the strength of the crust. Augustus and Peter Porter purchased this area and all of American Falls in 1805 from the New York state government, and enlarged the original canal to provide hydraulic power for their gristmill and tannery. The Earth's lithosphere is a patch work of plates in slow but constant motion (see plate tectonics). The first known effort to harness the waters was in 1759, when Daniel Joncairs built a small canal above the Falls to power his sawmill.

The word earthquake is also widely used to indicate the source region itself. The enormous energy of the Falls was long recognized as a potential source of power. Earthquakes typically result from the movement of faults, planar zones of deformation within the Earth's upper crust. The story of Niagara Falls in the 20th century is largely that of efforts to harness the energy of the Falls for hydroelectric power and to control the rampant development on both the American and Canadian sides which threatened the area's natural beauty. Earthquakes result from the dynamic release of elastic strain energy that radiates seismic waves. Especially after World War One, tourism boomed again as automobiles made getting to the Falls much easier. An earthquake is a sudden and sometimes catastrophic movement of a part of the Earth's surface. In 1941 the Niagara Falls Bridge Commission completed the third current crossing in the immediate area of Niagara Falls with the Rainbow Bridge, carrying both pedestrian and vehicular traffic.

Lake Tanganyika earthquake (2005). just below the Falls. Many more at risk from the Kashmiri winter. Known today as the Whirlpool Rapids Bridge, it carries vehicles, trains, and pedestrians between Canada and the U.S. Killed over 79,000 people. The first steel archway bridge near the Falls was completed in 1897. Kashmir earthquake (2005). In 1886 Leffert Buck replaced Roebling's wood and stone bridge with the predominantly steel bridge that still carries trains over the Niagara River today.

Fukuoka earthquake (2005). This was supplanted by German-American John Augustus Roebling's Niagara Falls Suspension Bridge in 1855. Sumatran Earthquake (2005). Demand for passage over the Niagara River led in 1848 to the building of a footbridge and then Charles Ellet's Niagara Suspension Bridge. Triggered a tsunami which caused nearly 300,000 deaths spanning several countries. Napoleon's brother visited with his bride in the early 19th century. Epicenter off the coast of the Indonesian island Sumatra. During the 19th century tourism became popular, and it was the area's main industry by mid-century.

One of the largest earthquakes ever recorded at 9.0. Hennepin County in Minnesota was named after Father Louis Hennepin. Indian Ocean Earthquake (2004). His subsequently discredited claim that he also traveled the Mississippi River to the Gulf of Mexico cast some doubt on the validity of his writings and sketches of Niagara Falls. Chuetsu Earthquake (2004). Hennepin also first described the Saint Anthony Falls in Minnesota. 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. Some credit Finnish-Swedish naturalist Pehr Kalm with the original first-hand description, penned during an expedition to the area early in the 18th century.3 Most historians however agree that Father Louis Hennepin observed and described the Falls much earlier, in 1677, after traveling in the region with explorer René Robert Cavelier, Sieur de la Salle, thus bringing them to the world's attention.

Parkfield, California earthquake (2004). Members of his party reported to him on the spectacular waterfalls, which he wrote of in his journals but may never have actually visited. Bam Earthquake (2003). The area was visited by Samuel de Champlain as early as 1604. Dudley Earthquake (2002). Some controversy exists over which European first gave a written, eyewitness description of the Falls. Gujarat Earthquake (2001). He-No caught her as she plummeted, and together their spirits are said to live forever in the Thunder God's sanctuary behind the Falls.

Nisqually Earthquake (2001). She paddled her canoe into the swift current of the Niagara River and was swept over the brink. Chi-Chi earthquake (1999). Rather than marry, Lelawala chose to sacrifice herself to her true love He-No, the Thunder God, who dwelled in a cave behind the Horseshoe Falls. Düzce earthquake (1999). Native American legend tells of Lelawala, a beautiful maid betrothed by her father to a brave she despised. İzmit earthquake (1999) Killed over 17,000 in northwestern Turkey. The name "Niagara" is said to originate from an Iroquois word "Onguiaahra" meaning "The Strait." The region's original inhabitants were the Ongiara, an Iroquois tribe named the Neutrals by French settlers, who found them helpful in mediating disputes with other tribes.

Killed over 6,400 people in and around Kobe, Japan. This volume is further halved at night, when most of the diversion to hydroelectric facilities occur. Great Hanshin earthquake (1995). The volume of water approaching the Falls during peak flow season is 202,000 ft³/s (5,720 m³/s).1,2 During the summer months, when maximum diversion of water for hydroelectric power occurs, 100,000 ft³/s (2,832 m³/s) of water actually traverses the Falls, some 90% of which goes over the Horseshoe Falls. Damage showed seismic resistance deficiencies in modern low-rise apartment construction. The larger Canadian Falls are about 2,600 feet (792 m) wide, while the American Falls are 1,060 feet (323 m) wide. Northridge, California earthquake (1994). The Falls drop about 170 feet (52 m), although the American Falls have a clear drop of only 70 feet (21 m) before reaching a jumble of fallen rocks which were deposited by a massive rock slide in 1954.

Revealed necessity of accelerated seismic retrofit of road and bridge structures. Engineers are working to reduce the rate of erosion to retard this event as long as possible. Severely affecting Santa Cruz, San Francisco and Oakland in California. Although erosion and recession have been slowed in this century by engineering, the falls will eventually recede far enough to drain most of Lake Erie, the bottom of which is higher than the bottom of the falls. Loma Prieta earthquake (1989). Just upstream from the Falls' current location, Goat Island splits the course of the Niagara River, resulting in the separation of the Horseshoe Falls to the west from the American and Bridal Veil Falls to the east. Killed over 25,000. The original Niagara Falls were near the sites of present-day Lewiston, New York, and Queenston, Ontario, but erosion of their crest has caused the waterfalls to retreat several miles southward.

Armenian earthquake (1988). All three formations were laid down in an ancient sea, and their differences of character derive from changing conditions within that sea. Whittier Narrows earthquake (1987). Submerged in the river in the lower valley, hidden from view, is the Queenston Formation (Upper Ordovician), which is composed of shales and fine sandstones. 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.). Because it erodes more easily, the river has undercut the hard cap rock and created the falls. Great Mexican Earthquake (1985). It is mainly shale, though it has some thin limestone layers, and contains large quantities of fossils.

The official death toll was 255,000, but many experts believe that two or three times that number died. Immediately below, comprising about two thirds of the cliff is the weaker, softer and more crumbly and sloping Rochester Formation (Lower Silurian). The most destructive earthquake of modern times. It is composed of very dense, hard and very strong limestone and dolostone. Tangshan earthquake (1976). The aerial photo clearly shows the hard caprock, the Lockport Formation (Middle Silurian), which underlies the rapids above the falls and approximately the upper third of the gorge wall. 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. When the newly established river encountered the erosion-resistant Lockport dolostone, the hard layer eroded much more slowly than the underlying softer rocks.

Sylmar earthquake (1971). Three major formations are exposed in the gorge that was cut by the Niagara River. Caused a landslide that buried the town of Yungay, Peru; killed over 40,000 people. In doing so it exposed old marine rocks that are much older than the geologically recent glaciation. Ancash earthquake (1970). In time the river cut a gorge across the Niagara Escarpment, the north facing cliff or cuesta formed by erosion of the southwardly dipping (tilted) and resistant Lockport formation between Lake Erie and Lake Ontario. Good Friday Earthquake (1964) Alaskan earthquake. After the ice melted back, drainage from the upper Great Lakes became the present-day Niagara River, which could not follow the old filled valley, so it found the lowest outlet on the rearranged topography.

Biggest earthquake ever recorded, 9.5 on Moment magnitude scale. It is thought that there is an old valley, buried by glacial drift, at the approximate location of the present Welland Canal. Great Chilean Earthquake (1960). It dammed others with debris, forcing these rivers to make new channels. Kamchatka earthquakes (1952 and 1737). The glacier drove through the area like a giant bulldozer, grinding up rocks and soil, moving them around, and deepening some river channels to make lakes. On the Japanese island of Honshu, killing over 140,000 in Tokyo and environs. Both the North American Great Lakes and the Niagara River are effects of this last continental ice sheet, an enormous glacier that crept across the area from eastern Canada.

Great Kanto earthquake (1923). The historical roots of Niagara Falls lie in the Wisconsin glaciation, which ended some 10,000 years ago. San Francisco Earthquake (1906). . Largest earthquake in the Southeast and killed 100. A popular tourist site for over a century, the natural wonder is shared between the twin cities of Niagara Falls, New York and Niagara Falls, Ontario. Charleston earthquake (1886). Niagara Falls is renowned for its beauty, and is both a valuable source of hydroelectric power and a challenging project for environmental preservation.

Fort Tejon Earthquake (1857). With more than 168,000 cubic metres (6 million cubic feet) of water falling over the crestline every minute [1] it is the most powerful waterfall in North America [2] and possibly the best-known in the world. New Madrid Earthquake (1811). While not exceptionally high, Niagara Falls is very wide. Lisbon earthquake (1755). Niagara Falls (French: chutes Niagara) comprises three separate waterfalls: the Horseshoe Falls (sometimes called the Canadian Falls), the American Falls, and the smaller, adjacent Bridal Veil Falls. Kamchatka earthquakes (1737 and 1952). Niagara Falls (43°4′54.68″N, 79°4′19.5″W) is a set of massive waterfalls located on the Niagara River in eastern North America, on the border between the United States and Canada.

Cascadia Earthquake (1700). Deadliest known earthquake in history, estimated to have killed 830,000 in China. Shaanxi Earthquake (1556). San Andreas Fault.

New Madrid Fault Zone. North Anatolian Fault Zone. Hayward Fault Zone. Calaveras Fault.

Alpine Fault. Earthquake prediction. Seismic retrofit. Household seismic safety.

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

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