EarthquakesEarthquakes

Godwin MangionGodwin Mangion

EarthquakeEarthquake

An earthquake is the result of a sudden release of energy in An earthquake is the result of a sudden release of energy in the earth’s crust that creates seismic waves. The the earth’s crust that creates seismic waves. The seismicity or seismic activity of an area refers to the seismicity or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over frequency, type and size of earthquakes experienced over a period of time. Earthquakes are measured using a period of time. Earthquakes are measured using observations from seismometers. The moment magnitude observations from seismometers. The moment magnitude of an earthquake is conventionally reported, with of an earthquake is conventionally reported, with magnitude 3 or lower earthquakes being mostly almost magnitude 3 or lower earthquakes being mostly almost imperceptible and magnitude 7 and over potentially imperceptible and magnitude 7 and over potentially causing serious damage over large areas, depending on causing serious damage over large areas, depending on their depth. The largest earthquakes in historic times have their depth. The largest earthquakes in historic times have been of magnitude slightly over 9, although there is no been of magnitude slightly over 9, although there is no limit to the possible magnitude. The most recent large limit to the possible magnitude. The most recent large earthquake of magnitude 9.0 or larger was a 9.0 earthquake of magnitude 9.0 or larger was a 9.0 magnitude earthquake in Japan 2011, and it was the magnitude earthquake in Japan 2011, and it was the largest Japanese earthquake since records began. The largest Japanese earthquake since records began. The shallower an earthquake, the more damage to structures it shallower an earthquake, the more damage to structures it causes, all else being equal. causes, all else being equal.

Earthquake fault typesEarthquake fault typesThere are three main types of fault that may cause an There are three main types of fault that may cause an

earthquake: normal, thrust and strike-slip. Normal earthquake: normal, thrust and strike-slip. Normal and reverse faulting are examples of dip-slip, where and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of the displacement along the fault is in the direction of dip and movement on them involves a vertical dip and movement on them involves a vertical component. Normal faults occur mainly in areas component. Normal faults occur mainly in areas where the crust is being extended such as a where the crust is being extended such as a divergent boundaries. Reverse faults occur in areas divergent boundaries. Reverse faults occur in areas where the crust is being shortened such as at a where the crust is being shortened such as at a convergent boundary. Strike-slip faults are steep convergent boundary. Strike-slip faults are steep structures where the two sides of the fault slip structures where the two sides of the fault slip horizontally past each other; transform boundaries horizontally past each other; transform boundaries are a particular type of strike-slip fault. Many are a particular type of strike-slip fault. Many earthquakes are caused by movement on faults that earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this have components of both dip-slip and strike-slip; this is known as oblique slip. Reverse faults, particularly is known as oblique slip. Reverse faults, particularly those along convergent plate boundaries are those along convergent plate boundaries are associated with the most powerful earthquakes, associated with the most powerful earthquakes, including almost all of those of magnitude 8 or more. including almost all of those of magnitude 8 or more. Strike-slip faults, particularly transforms can Strike-slip faults, particularly transforms can produce major earthquakes up to about magnitude produce major earthquakes up to about magnitude 8. Earthquakes associated with normal faults are 8. Earthquakes associated with normal faults are generally less than magnitude 7. generally less than magnitude 7.

Major earthquakesMajor earthquakes

One of the most devastating earthquakes in recorded history occurred on 23 One of the most devastating earthquakes in recorded history occurred on 23 January 1556 in the Shaanxi province, China, killing more than 830,000 January 1556 in the Shaanxi province, China, killing more than 830,000 people. Most of the population in the area at the time lived in yaodongs, people. Most of the population in the area at the time lived in yaodongs, artificial caves in loess cliffs, many of which collapsed during the artificial caves in loess cliffs, many of which collapsed during the catastrophe with great loss of life. The 1976 Tangshan earthquake, with catastrophe with great loss of life. The 1976 Tangshan earthquake, with death toll estimated to be between 240,000 to 655,000, is believed to be death toll estimated to be between 240,000 to 655,000, is believed to be the largest earthquake of the 20th century by death toll. The largest the largest earthquake of the 20th century by death toll. The largest earthquake that has been measured on a seismograph reached 9.5 earthquake that has been measured on a seismograph reached 9.5 magnitude, occurring on 22 May 1960. Its epicenter was near Cañete, magnitude, occurring on 22 May 1960. Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday Earthquake, which was centered in powerful earthquake, the Good Friday Earthquake, which was centered in Prince William Sound, Alaska. The ten largest recorded earthquakes have Prince William Sound, Alaska. The ten largest recorded earthquakes have all been megathrust earthquakes; however, of these ten, only the 2004 all been megathrust earthquakes; however, of these ten, only the 2004 Indian Ocean earthquake is simultaneously one of the deadliest Indian Ocean earthquake is simultaneously one of the deadliest earthquakes in history. Earthquakes that caused the greatest loss of life, earthquakes in history. Earthquakes that caused the greatest loss of life, while powerful, were deadly because of their proximity to either heavily while powerful, were deadly because of their proximity to either heavily populated areas or the ocean, where earthquakes often create tsunamis populated areas or the ocean, where earthquakes often create tsunamis that can devastate communities thousands of kilometers away. Regions that can devastate communities thousands of kilometers away. Regions most at risk for great loss of life include those where earthquakes are most at risk for great loss of life include those where earthquakes are relatively rare but powerful, and poor regions with lax, unenforced, or relatively rare but powerful, and poor regions with lax, unenforced, or nonexistent seismic building codes.nonexistent seismic building codes.

Naturally occurring Naturally occurring earthquakesearthquakes

Tectonic earthquakes occur anywhere in the earth where there is Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increase the frictional asperities along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behaviour. Once the fault has locked, continued to a form of stick-slip behaviour. Once the fault has locked, continued relative motion between the plates leads to increasing stress and relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred stress punctuated by occasional sudden earthquake failure is referred to as the. Most of the earthquake's energy is used to power the to as the. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic-friction. Therefore, earthquakes lower the Earth's available elastic-rebound theory and raise its temperature, though these changes are rebound theory and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat negligible compared to the conductive and convective flow of heat out from the Earth's deep interior. out from the Earth's deep interior.

AftershocksAftershocks

An aftershock is a smaller earthquake An aftershock is a smaller earthquake that occurs after a previous large that occurs after a previous large earthquake, in the same area of the earthquake, in the same area of the main shock. If an aftershock is larger main shock. If an aftershock is larger than the main shock, the aftershock is than the main shock, the aftershock is redesignated as the main shock and the redesignated as the main shock and the original main shock is redesignated as a original main shock is redesignated as a foreshock. Aftershocks are formed as foreshock. Aftershocks are formed as the crust around the displaced fault the crust around the displaced fault plane adjusts to the effects of the main plane adjusts to the effects of the main shock. shock.

Earthquake swarmEarthquake swarm

Earthquake swarms are events where a local area Earthquake swarms are events where a local area experiences sequences of many earthquakes striking in a experiences sequences of many earthquakes striking in a relatively short period of time. The length of time used to relatively short period of time. The length of time used to define the swarm itself varies, but the United States define the swarm itself varies, but the United States Geological Survey points out that an event may be on the Geological Survey points out that an event may be on the order of days, weeks, or months. They are differentiated order of days, weeks, or months. They are differentiated from earthquakes succeeded by a series of aftershocks by from earthquakes succeeded by a series of aftershocks by the observation that no single earthquake in the sequence the observation that no single earthquake in the sequence is obviously the main shock. Earthquake swarms are one of is obviously the main shock. Earthquake swarms are one of the events typically preceding eruptions of volcanoes. One the events typically preceding eruptions of volcanoes. One example is along the Cerro Prieto Fault near Mexicali, BC in example is along the Cerro Prieto Fault near Mexicali, BC in Mexico where over 500 quakes and aftershocks hit in Mexico where over 500 quakes and aftershocks hit in February, 2008. Another is a swarm that's been dubbed February, 2008. Another is a swarm that's been dubbed "The Mogul earthquake sequence" that began in February "The Mogul earthquake sequence" that began in February 2008 near Reno, Nevada and continued for several months, 2008 near Reno, Nevada and continued for several months, ending in November 2008. Between February and April the ending in November 2008. Between February and April the swarm produced more than 1,000 quakes of small swarm produced more than 1,000 quakes of small magnitude, although the largest measured 4.7.magnitude, although the largest measured 4.7.

How does a tsunami occurHow does a tsunami occur

As a tsunami leaves the deep water of the open As a tsunami leaves the deep water of the open ocean and travels into the shallower water near the ocean and travels into the shallower water near the coast, it transforms. A tsunami travels at a speed coast, it transforms. A tsunami travels at a speed that is related to the water depth - hence, as the that is related to the water depth - hence, as the water depth decreases, the tsunami slows. The water depth decreases, the tsunami slows. The tsunami's energy flux, which is dependent on both tsunami's energy flux, which is dependent on both its wave speed and wave height, remains nearly its wave speed and wave height, remains nearly constant. Consequently, as the tsunami's speed constant. Consequently, as the tsunami's speed diminishes as it travels into shallower water, its diminishes as it travels into shallower water, its height grows. Because of this shoaling effect, a height grows. Because of this shoaling effect, a tsunami, imperceptible at sea, may grow to be tsunami, imperceptible at sea, may grow to be several meters or more in height near the coast. several meters or more in height near the coast.

TsunamiTsunami

A A tsunamitsunami is a series of water waves caused by the is a series of water waves caused by the displacement of a large volume of a body of water, usually displacement of a large volume of a body of water, usually an ocean, though it can occur in large lakes. Owing to the an ocean, though it can occur in large lakes. Owing to the immense volumes of water and the high energy involved, immense volumes of water and the high energy involved, tsunamis can devastate coastal regions.The Greek historian tsunamis can devastate coastal regions.The Greek historian Thucydides was the first to relate tsunami to submarine Thucydides was the first to relate tsunami to submarine earthquakes, but the understanding of a tsunami's nature earthquakes, but the understanding of a tsunami's nature remained slim until the 20th century and is the subject of remained slim until the 20th century and is the subject of ongoing research. Many early geological, geographical, and ongoing research. Many early geological, geographical, and oceanographic texts refer to tsunamis as "oceanographic texts refer to tsunamis as "seismic sea seismic sea waves”waves”.Some meteorological conditions, such as deep .Some meteorological conditions, such as deep depressions that cause tropical cyclones, can generate a depressions that cause tropical cyclones, can generate a storm surge, called a meteotsunami, which can raise tides storm surge, called a meteotsunami, which can raise tides several metres above normal levels. The displacement several metres above normal levels. The displacement comes from low atmospheric pressure within the centre of comes from low atmospheric pressure within the centre of the depression. As these storm surges reach shore, they the depression. As these storm surges reach shore, they may resemble tsunamis, inundating vast areas of land.may resemble tsunamis, inundating vast areas of land.

VolcanoesVolcanoes

A volcano is an opening, or rupture, in a planet's A volcano is an opening, or rupture, in a planet's surface or crust, which allows hot magma, surface or crust, which allows hot magma, volcanic ash and gases to escape from below the volcanic ash and gases to escape from below the surface. Volcanoes are generally found where surface. Volcanoes are generally found where tectonic plates are diverging or converging. A tectonic plates are diverging or converging. A mid-oceanic ridge, for example the Mid-Atlantic mid-oceanic ridge, for example the Mid-Atlantic Ridge, has examples of volcanoes caused by Ridge, has examples of volcanoes caused by divergent tectonic plates pulling apart; the divergent tectonic plates pulling apart; the Pacific Ring of Fire has examples of volcanoes Pacific Ring of Fire has examples of volcanoes caused by convergent tectonic plates coming caused by convergent tectonic plates coming together. By contrast, volcanoes are usually not together. By contrast, volcanoes are usually not created where two tectonic plates slide past one created where two tectonic plates slide past one another. Volcanoes can also form where there is another. Volcanoes can also form where there is stretching and thinning of the Earth's crust in stretching and thinning of the Earth's crust in the interiors of plates, e.g., in the East African the interiors of plates, e.g., in the East African Rift, the Wells Gray-Clearwater volcanic field and Rift, the Wells Gray-Clearwater volcanic field and the Rio Grande Rift in North America. This type the Rio Grande Rift in North America. This type of volcanism falls under the umbrella of "Plate of volcanism falls under the umbrella of "Plate hypothesis" volcanism. Intraplate volcanism has hypothesis" volcanism. Intraplate volcanism has also been postulated to be caused by mantle also been postulated to be caused by mantle plumes. These so-called "hotspots", for example plumes. These so-called "hotspots", for example Hawaii, are postulated to arise from upwelling Hawaii, are postulated to arise from upwelling diapirs from the core-mantle boundary, 3,000 km diapirs from the core-mantle boundary, 3,000 km deep in the Earth.deep in the Earth.

FloodsFloods

A flood is an overflow of an expanse of water that submerges land. The A flood is an overflow of an expanse of water that submerges land. The EU Floods directive defines a flood as a temporary covering by water EU Floods directive defines a flood as a temporary covering by water of land not normally covered by water. In the sense of "flowing of land not normally covered by water. In the sense of "flowing water", the word may also be applied to the inflow of the tide. water", the word may also be applied to the inflow of the tide. Flooding may result from the volume of water within a body of Flooding may result from the volume of water within a body of water, such as a river or lake, which overflows or breaks levees, water, such as a river or lake, which overflows or breaks levees, with the result that some of the water escapes its usual boundaries. with the result that some of the water escapes its usual boundaries. While the size of a lake or other body of water will vary with While the size of a lake or other body of water will vary with seasonal changes in precipitation and snow melt, it is not a seasonal changes in precipitation and snow melt, it is not a significant flood unless such escapes of water endanger land areas significant flood unless such escapes of water endanger land areas used by man like a village, city or other inhabited area. Floods can used by man like a village, city or other inhabited area. Floods can also occur in rivers, when flow exceeds the capacity of the river also occur in rivers, when flow exceeds the capacity of the river channel, particularly at bends or meanders. Floods often cause channel, particularly at bends or meanders. Floods often cause damage to homes and businesses if they are placed in natural flood damage to homes and businesses if they are placed in natural flood plains of rivers. While flood damage can be virtually eliminated by plains of rivers. While flood damage can be virtually eliminated by moving away from rivers and other bodies of water, since time out moving away from rivers and other bodies of water, since time out of mind, people have lived and worked by the water to seek of mind, people have lived and worked by the water to seek sustenance and capitalize on the gains of cheap and easy travel and sustenance and capitalize on the gains of cheap and easy travel and commerce by being near water. commerce by being near water.

LandslidesLandslides

A landslide or landslip is a geological A landslide or landslip is a geological phenomenon which includes a wide range of phenomenon which includes a wide range of ground movement, such as rock falls, deep ground movement, such as rock falls, deep failure of slopes and shallow debris flows, failure of slopes and shallow debris flows, which can occur in offshore, coastal and which can occur in offshore, coastal and onshore environments. Although the action onshore environments. Although the action of gravity is the primary driving force for a of gravity is the primary driving force for a landslide to occur, there are other landslide to occur, there are other contributing factors affecting the original contributing factors affecting the original slope stability. Typically, pre-conditional slope stability. Typically, pre-conditional factors build up specific sub-surface factors build up specific sub-surface conditions that make the area/slope prone to conditions that make the area/slope prone to failure, whereas the actual landslide often failure, whereas the actual landslide often requires a trigger before being released.requires a trigger before being released.

THE ENDTHE END

By Godwin MangionBy Godwin Mangion 3.33.3