This page will contain blogs about Earthquakes, as they become available.

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 Earthquakes includes information from a Wikipedia article.
Additional articles about Earthquakes
News stories about Earthquakes
External links for Earthquakes
Videos for Earthquakes
Wikis about Earthquakes
Discussion Groups about Earthquakes
Blogs about Earthquakes
Images of Earthquakes

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. Business jets are typically flown by commercial pilots, although there is a new generation of small jets arriving soon for private pilots. 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. Piston-powered propeller aircraft (single-engine or twin-engine) are especially common for both private and commercial general aviation, but even private pilots occasionally own and operate helicopters like the Bell JetRanger or turboprops like the Beechcraft King Air. Another type of movement of the Earth is observed by terrestrial spectroscopy. Commercial general aviation pilots use aircraft for a wide range of tasks, such as flight training, pipeline surveying, passenger and freight transport, policing, crop dusting, and medical transport (medevac). Earthquakes such as these, that are caused by human activity, are referred to by the term induced seismicity. Usually these private pilots own their own aircraft and take out loans from banks or specialized lenders to purchase them.

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. Private pilots use aircraft primarily for personal travel, business travel, or recreation. Finally, ground shaking can also result from the detonation of explosives. Within general aviation, the major distinction is between private flights (where the pilot is not paid for time or expenses) and commercial flights (where the pilot is paid by a customer or employer). Earthquakes have also been known to be caused by the removal of natural gas from subsurface deposits, for instance in the northern Netherlands. The vast majority of flights flown around the world each day belong to the general aviation category, ranging from recreational balloon flying to civilian flight training to business trips to firefighting to medevac flights to cargo transportation on freight aircraft. Such earthquakes occur because the strength of the Earth's crust can be modified by fluid pressure. Civil aviation includes both scheduled airline flights and general aviation, a catch-all covering other kinds of private and commercial use.

at certain geothermal power plants and at the Rocky Mountain Arsenal). By the time of the Vietnam War, helicopters had come into widespread military use, especially for transporting and supporting ground troops. 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. Tankers were developed after World War II to refuel other aircraft in mid-air, thus increasing their operational range. Some earthquakes are also caused by the movement of magma in volcanoes, and such quakes can be an early warning of volcanic eruptions. In order to prevent the enemy from bombing, fighter aircraft were developed to intercept and shoot down enemy aircraft. 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. During World War I many types of aircraft were adapted for attacking the ground or enemy vehicles/ships/guns/aircraft, and the first aircraft designed as bombers were born.

Eventually when enough stress accumulates, the plates move, causing an earthquake. Combat aircraft themselves, though used a handful of times for reconnaissance and surveillance during the Italo-Turkish War, did not come into widespread use until the Balkan War when first air-dropped bomb was invented and widely used by Bulgarian air force against Turkey. Where these plates meet stress accumulates. In the past, gliders and balloons have also been used as military aircraft; for example, balloons were used for observation during the American Civil War and World War I, and cargo gliders were used during World War II to land intruding German troops in many European countries in the 1940/42 period, while Allied troops used them in Europe after D-Day . The Earth is made up of tectonic plates driven by the heat in the Earth's mantle and core. Even the little fabric-covered two-seater Piper J3 Cub had a military version, the L-4 liaison, observation and trainer aircraft. 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. military and the Dakota in Britain and the Commonwealth.

For example it has been calculated that the average recurrence for the United Kingdom can be described as follows:. Many civil aircraft have been produced in separate models for military use, such as the civil Douglas DC-3 airliner, which became the military C-47/C-53/R4D transport in the U.S. 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. Combat aircraft like fighters or bombers represent only a minority of the category. 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. The major distinction in aircraft usage is between military aviation, which includes all uses of aircraft for military purposes (such as combat, patrolling, search and rescue, reconnaissance, transport, and training), and civil aviation, which includes all uses of aircraft for non-military purposes. The values of moments for different earthquakes ranges over several order of magnitude. They are restricted to rather specialised niches, such as spaceflight, where no oxygen is available for combustion (rockets carry their own oxygen).

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. Rocket aircraft have occasionally been experimented with. 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. In addition to turbine engines like the turboprop and turbojet, other types of high-altitude, high-performance engines have included the ramjet and the pulse jet. 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. Helicopters also typically use turbine engines. 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. Pressurised aircraft, however, are more likely to use the turbine engine, since it is naturally efficient at higher altitudes and can operate above 40,000 ft.

Each of these is scaled to gives values similar to the values given by the Richter scale. During the forties and especially following the 1973 energy crisis, development work was done on propellers with swept tips or even scimitar-shaped blades for use in high-speed commercial and military transports. Other more recent Magnitude measurements include: body wave magnitude (mb), surface wave magnitude (Ms) and duration magnitude (MD). Piston engines normally become less efficient above 7,000-8,000 ft (2100-2400 m) above sea level because there is less oxygen available for combustion; to solve that problem, some piston engines have mechanically powered compressors (blowers) or turbine-powered turbochargers or turbonormalizers that compress the air before feeding it into the engine; these piston engines can often operate efficiently at 20,000 ft (6100 m) above sea level or higher, altitudes that require the use of supplemental oxygen or cabin pressurisation. 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. Piston engines typically operate using avgas or regular gasoline, though some new ones are being designed to operate on diesel or jet fuel. This is known as the “Richter scale”, “Richter Magnitude” or “Local Magnitude” (ML). Water cooled V engines, as used in automobiles, were common in high speed aircraft, until they were replaced by jet and turbine power.

Richter devised a simple numerical scale (which he called the magnitude) to describe the relative sizes of earthquakes in Southern California. (See also: Aircraft engine.) The piston engine is still used in the majority of aircraft produced, since it is efficient at the lower altitudes used by small aircraft, but the radial engine (with the cylinders arranged in a circle around the crankshaft) has largely given way to the horizontally-opposed engine (with the cylinders lined up on two sides of the crankshaft). In the 1930s, a California seismologist named Charles F. Until World War II, the internal combustion piston engine was virtually the only type of propulsion used for powered aircraft. 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). Airships combine a balloon's buoyancy with some kind of propulsion, usually propeller driven. If you feel an earthquake in the US you can report the effects to the USGS. For gliders, takeoff takes place from a high location, or the aircraft is pulled into the air by a ground-based winch or vehicle, or towed aloft by a powered "tug" aircraft.

For some tasks related to engineering and local planning it is still useful for the very same reasons and thus still collected. Balloons drift with the wind, though normally the pilot can control the altitude either by heating the air or by releasing ballast, giving some directional control (since the wind direction changes with altitude). 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. Some types of aircraft, such as the balloon or glider, do not have any propulsion. No structural damage. These designs may have potential but are not yet practical. Damage is slight in poorly built buildings. And finally the flapping-wing ornithopter is a category of its own.

Trees and bushes shake. It is (2005) in development in the United Kingdom. Plaster in walls might crack. This uses a fixed wing with a forced airflow produced by cylindrical fans mounted above. Furniture moves. A recent innovation is a completely new class of aircraft, the fan wing. Pictures fall off walls. A further category might encompass the wing-in-ground-effect types, for example the Russian ekranoplan also nicknamed the "Caspian Sea Monster" and hovercraft; most of the latter employing a skirt and achieving limited ground or water clearance to reduce friction and achieve speeds above those achieved by boats of similar weight.

Objects fall from shelves. Some craft have reaction-powered rotors with gas jets at the tips but most have one or more lift rotors powered from engine-driven shafts. People have trouble walking. The best-known examples are the helicopter, the autogyro and the tiltrotor aircraft (such as the V-22 Osprey). Everyone feels movement. Here, the lift is provided by rotating aerofoils or rotors. The value 6 (normally denoted "VI") in the MM scale for example is:. A second category of aerodynamically lifted aircraft are the rotary-wing aircraft.

These assign a numeric value (different for each scale) to a location based on the size of the shaking experienced there. So far the only significant practical application of the lifting body is in the Space Shuttle, but many aircraft generate lift from nothing other than wings alone. 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. The lifting body configuration is where the body itself produce lift. The first method of quantifying earthquakes was intensity scales. A variable geometry ('swing-wing') has also been employed in a few examples of combat aircraft (the F-111, Panavia Tornado, F-14 Tomcat and B-1 Lancer, among others). 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. the B-2 Spirit).

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. Other possibilities include the delta-wing, where lift and horizontal control surfaces are often combined, and the flying wing, where there is no separate vertical control surface (e.g. The total size of the fault that slips, the rupture zone, can be as large as 1000 km, for the biggest earthquakes. This is principally an improvement in structures and not aerodynamics. The location on the surface directly above the hypocenter is known as the "epicenter". Subsequently most aircraft are monoplanes. That point is called its "focus" or "hypocenter" and usually proves to be the point at which the fault slip was initiated. The number of lift surfaces varied in the pre-1950 period, as biplanes (two wings) and triplanes (three wings) were numerous in the early days of aviation.

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. Canards are becoming more common as supersonic aerodynamics grows more mature and because the forward surface contributes lift during straight-and-level flight. 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. The other configuration is the canard where small horizontal control surfaces are placed forward of the wings, near the nose of the aircraft. Ground motions caused by very distant earthquakes are called teleseisms. In a "conventional" configuration, the lift surfaces are placed in front of a control surface or tailplane. 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. Much aerodynamic work was done with kites until test aircraft, wind tunnels and now computer modelling programs became available.

While almost all earthquakes have aftershocks, foreshocks are far less common occurring in only about 10% of events. Kites depend upon the tension between the cord which anchors it to the ground and the force of the wind currents. 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. The forerunner of these type of aircraft is the kite. S-waves (secondary or shear waves) and the two types of surfaces waves (Love waves and Rayleigh waves) are responsible for the shaking hazard. Among aerodynamically lifted aircraft, most fall in the category of fixed-wing aircraft, where horizontal airfoils produce lift, by profiting from airflow patterns determined by Bernoulli's equation and, to some extent, the Coanda effect. There are four types of seismic waves that are all generated simultaneously and can be felt on the ground. With engine lift, the aircraft defeats gravity by use of vertical Examples of engine lift aircraft are rockets, and VTOL aircraft such as the Hawker-Siddeley Harrier.

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. In the case of aerodynamic lift, the aircraft is kept in the air by wings or rotors (see aerodynamics). liquefaction, landslide), and fire or a release of hazardous materials. In heavier-than-air aircraft, there are two ways to produce lift: aerodynamic lift and engine lift. 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. Several accidents, such as the Hindenburg fire at Lakehurst, NJ, in 1937 led to the demise of large rigid airships. Some deep earthquakes may be due to the transition of olivine to spinel, which is more stable in the deep mantle. The most successful type of rigid airship was the Zeppelin.

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. Examples of lighter-than-air aircraft include non-steerable balloons, such as hot air balloons and gas balloons, and steerable airships (sometimes called dirigible balloons) such as blimps (that have non-rigid construction) and rigid airships that have an internal frame. Where the crust is thicker and colder they will occur at greater depths and the opposite in areas that are hot. A first division by design among aircraft is between lighter-than-air, aerostat, and heavier-than-air aircraft, aerodyne. 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. Below, we describe classifications by design, propulsion and usage. 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 . There are several ways to classify aircraft.

. Aircraft fall into two broad categories:. 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. . 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. An aircraft is any machine capable of atmospheric flight. Earthquakes related to plate tectonics are called tectonic earthquakes. The distinction between a balloon and an airship is that an airship has some means of controlling both its forward motion and steering itself, while balloons are carried along with the wind.

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 particular, these aircraft use a relatively low density gas such as helium, hydrogen or heated air, to displace the air around the craft. 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. Aerostats use buoyancy to float in the air in much the same manner as ships float on the water. Earthquakes occur where the stress resulting from the differential motion of these plates exceeds the strength of the crust. Lighter than air aerostats: hot air balloons and airships. The Earth's lithosphere is a patch work of plates in slow but constant motion (see plate tectonics). Mainly used internationally.

The word earthquake is also widely used to indicate the source region itself. STOL stands for Short Take Off and Landing. Earthquakes typically result from the movement of faults, planar zones of deformation within the Earth's upper crust. The abbreviation VTOL is applied to aircraft other than helicopters that can take off or land vertically. Earthquakes result from the dynamic release of elastic strain energy that radiates seismic waves. Helicopters and autogyros use a spinning rotor (a rotary wing) to provide lift; helicopters also use the rotor to provide thrust. An earthquake is a sudden and sometimes catastrophic movement of a part of the Earth's surface. For a glider to maintain its forward speed it must descend in relation to the air (but not necessarily in relation to the ground).

Lake Tanganyika earthquake (2005). Exceptions are gliders which have no engines and gain their thrust, initially, from winches or tugs and then from gravity and thermal currents. Many more at risk from the Kashmiri winter. The movement of air over the airfoil produces lift that causes the aircraft to fly. Killed over 79,000 people. Fixed-wing aircraft generally use an internal-combustion engine in the form of a piston engine (with a propeller) or a turbine engine (jet or turboprop), to provide thrust that moves the craft forward through the air. Kashmir earthquake (2005). Heavier than air aerodynes, including autogyros, helicopters and variants, and conventional fixed-wing aircraft: aeroplanes in Commonwealth English (excluding Canada), airplanes in North American English.

Fukuoka earthquake (2005). Sumatran Earthquake (2005). Triggered a tsunami which caused nearly 300,000 deaths spanning several countries. Epicenter off the coast of the Indonesian island Sumatra.

One of the largest earthquakes ever recorded at 9.0. Indian Ocean Earthquake (2004). Chuetsu 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.

Parkfield, California earthquake (2004). Bam Earthquake (2003). Dudley Earthquake (2002). Gujarat Earthquake (2001).

Nisqually Earthquake (2001). Chi-Chi earthquake (1999). Düzce earthquake (1999). İzmit earthquake (1999) Killed over 17,000 in northwestern Turkey.

Killed over 6,400 people in and around Kobe, Japan. Great Hanshin earthquake (1995). Damage showed seismic resistance deficiencies in modern low-rise apartment construction. Northridge, California earthquake (1994).

Revealed necessity of accelerated seismic retrofit of road and bridge structures. Severely affecting Santa Cruz, San Francisco and Oakland in California. Loma Prieta earthquake (1989). Killed over 25,000.

Armenian earthquake (1988). Whittier Narrows earthquake (1987). 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.). Great Mexican Earthquake (1985).

The official death toll was 255,000, but many experts believe that two or three times that number died. The most destructive earthquake of modern times. Tangshan earthquake (1976). 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.

Sylmar earthquake (1971). Caused a landslide that buried the town of Yungay, Peru; killed over 40,000 people. Ancash earthquake (1970). Good Friday Earthquake (1964) Alaskan earthquake.

Biggest earthquake ever recorded, 9.5 on Moment magnitude scale. Great Chilean Earthquake (1960). Kamchatka earthquakes (1952 and 1737). On the Japanese island of Honshu, killing over 140,000 in Tokyo and environs.

Great Kanto earthquake (1923). San Francisco Earthquake (1906). Largest earthquake in the Southeast and killed 100. Charleston earthquake (1886).

Fort Tejon Earthquake (1857). New Madrid Earthquake (1811). Lisbon earthquake (1755). Kamchatka earthquakes (1737 and 1952).

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.

08-28-14 FTPPro Support FTPPro looks and feels just like Windows Explorer Contact FTPPro FTPPro Help Topics FTPPro Terms Of Use ftppro.com/1stzip.php ftppro.com/zip ftppro.com/browse2000.php PAD File Directory Business Search Directory Real Estate Database FunWebsites.org PressArchive.net WebExposure.us Display all your websites in one place HereIam.tv Celebrity Homepages Charity Directory Google+ Directory Move your favorite Unsigned Artist to the Top of the List