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    Earthquake Earthquake Presentation Transcript

    • A POWERPOINT ON
    • WHAT IS AN EARTHQUAKE? An earthquake (also known as a quake, tremor or temblor) is the result of a sudden release of energy in the Earth's crust that creates seismic waves. The seismicity, seismism or seismic activity of an area refers to the frequency, type and size of earthquakes experienced over a period of time. Earthquakes are measured using observations from seismometers. The moment magnitude is the most common scale on which earthquakes larger than approximately 5 are reported for the entire globe. The more numerous earthquakes smaller than magnitude 5 reported by national seismological observatories are measured mostly on the local magnitude scale, also referred to as the Richter scale. These two scales are numerically similar over their range of validity. Magnitude 3 or lower earthquakes are mostly almost imperceptible or weak and magnitude 7 and over potentially cause serious damage over larger areas, depending on their depth. The largest earthquakes in historic times have been of magnitude slightly over 9, although there is no limit to the possible magnitude. The most recent large earthquake of magnitude 9.0 or larger was a 9.0 magnitude earthquake in Japan in 2011 (as of October 2012), and it was the largest Japanese earthquake since records began. Intensity of shaking is measured on the modified Mercalli scale. The shallower an earthquake, the more damage to structures it causes, all else being equal.[1] At the Earth's surface, earthquakes manifest themselves by shaking and sometimes displacement of the ground. When the epicenter of a large earthquake is located offshore, the seabed may be displaced sufficiently to cause a tsunami. Earthquakes can also trigger landslides, and occasionally volcanic activity.
    • MAPS OF EARTHQUAKES
    • MAJOR EARTHQUAKES One of the most devastating earthquakes in recorded history occurred on 23 January 1556 in the Shaanxi province, China, killing more than 830,000 people (see 1556 Shaanxi earthquake).[56] Most of the population in the area at the time lived in yaodongs, artificial caves in loess cliffs, many of which collapsed during the catastrophe with great loss of life. The 1976 Tangshan earthquake, with a 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.[57] The 1960 Chilean Earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960.[29][30] Its epicenter was near Cañete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday Earthquake, which was centered in Prince William Sound, Alaska.[58][59] The ten largest recorded earthquakes have all been megathrust earthquakes; however, of these ten, only the 2004 Indian Ocean earthquake is simultaneously one of the deadliest earthquakes in history. Earthquakes that caused the greatest loss of life, while powerful, were deadly because of their proximity to either heavily populated areas or the ocean, where earthquakes often create tsunamis that can devastate communities thousands of kilometers away. Regions most at risk for great loss of life include those where earthquakes are relatively rare but powerful, and poor regions with lax, unenforced, or nonexistent seismic building codes.
    • NATURALLY OCCURRING EARTHQUAKE Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain Tectonic earthquakes occur anywhere in the earth where there is energy to drive fracture strain energyalong a fault plane. The sides of a fault move past each other sufficient stored elastic propagation to drive fracture propagation along smoothly andThe sides of aonly ifmove past no irregularities or asperities along the fault surface a fault plane. aseismically fault there are each other smoothly and that increase only if there are no irregularities or surfaces do havethe fault aseismically the frictional resistance. Most fault asperities along such asperities and this leads to a form of stick-slip behaviour. Once the fault Most fault surfaces do relative motion between the surface that increase the frictional resistance. has locked, continued have plates leads to increasing stress and therefore, stored strain energy in the volume around the fault such asperities and this leads to a form of stick-slip behaviour. Once the surface. This continues until the stress has risen sufficiently to leads to fault has locked, continued relative motion between the plates break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This increasing stress and therefore, stored strain energy in the volume around energy issurface. This continues until the stress elastic strain seismic waves, frictional heating of the fault released as a combination of radiated has risen sufficiently to the fault surface, and cracking of the allowing sliding over the locked This process of gradual break through the asperity, suddenly rock, thus causing an earthquake. build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as portion of the fault, releasing the stored energy. This energy is released as the elastic-rebound theory.elastic strain seismic waves,percent or heatingan earthquake's total a combination of radiated It is estimated that only 10 frictional less of energyfault surface, and cracking of the rock, the earthquake'searthquake. of the is radiated as seismic energy. Most of thus causing an energy is used to power the earthquake fracture growth or is converted into heat punctuated by This process of gradual build-up of strain and stress generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these occasional sudden earthquake failure is referred to as the elastic-rebound changes are estimated that only 10 percent or less of an earthquake's total heat out from the theory. It is negligible compared to the conductive and convective flow of Earth's is radiated as [2] energy deep interior. seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available
    • EARTHQUAKE FAULT TYPES There are three main types of fault, all of which maythe earth where there is sufficient stored elastic strain Tectonic earthquakes occur anywhere in cause an earthquake: normal, reverse (thrust) and strike-slip. Normal and reverse faulting are examples of dipenergy tothe displacement along the fault is in the direction ofplane. The sides of a fault move past each other drive fracture propagation along a fault dip and slip, where smoothly and aseismically only if there Normal faults occur mainly inasperities along the fault surface movement on them involves a vertical component. are no irregularities or areas where the the frictional resistance. divergent boundary. Reverse that increasecrust is being extended such as aMost fault surfaces do have such asperities and this leads to faults occur in areas where the crust is being shortened such as at a convergent a form of stick-slip behaviour. Once the fault has locked, continued relative motion between the boundary. Strike-slip faults are steep structures where the two sides of the fault plates leads to increasing stress and therefore,astored strain of slip horizontally past each other; transform boundaries are particular type energy in the volume around the fault surface. fault. Many earthquakes are caused by movement on faults that have break through the asperity, strike-slip This continues until the stress has risen sufficiently to components allowing slidingstrike-slip; this is known as obliquethe fault, releasing the stored energy. This suddenly of both dip-slip and over the locked portion of slip. Reverse faults, particularly those along convergent plate boundaries are associated energymost powerful as a combination of radiatedthose of magnitude 8 is released earthquakes, including almost all of elastic strain seismic waves, frictional heating of with the the fault surface, andparticularly continental transformscausing anmajor or more. Strike-slip faults, cracking of the rock, thus can produce earthquake. This process of gradual earthquakesof strain and stress8. Earthquakes associated with normal faults build-up up to about magnitude punctuated by occasional sudden earthquake failure is referred to as are generally less than magnitude 7. is estimated that only 10 percent or less of an earthquake's total the elastic-rebound theory. It This is so because the energy released in an earthquake, and thus its magnitude, is energy is radiated as the fault that rupturesMost the the earthquake's energy is used to power the proportional to the area of seismic energy. [3] and of stress drop. Therefore, earthquake length and the wider the is converted into heat generated by friction. Therefore, earthquakes the longer the fracture growth or width of the faulted area, the larger the resulting magnitude. The topmost, elastic potential energy andthe coolits temperature, though these lower the Earth's available brittle part of the Earth's crust, and raise slabs of the tectonic plates that are descending down into the hot mantle, are the changes of our planet whichcompared to the conductive and fault are negligible can store elastic energy and release it in convective flow of heat out from the only parts Earth's Rocks hotter than[2] 300 degrees Celsius flow in response to stress; ruptures. deep interior. about they do not rupture in earthquakes.[4][5] The maximum observed lengths of ruptures and mapped faults, which may break in one go are approximately 1000 km. Examples are the earthquakes in Chile, 1960; Alaska, 1957; Sumatra, 2004, all in
    • The most important parameter controlling the the earth where there is sufficient stored elastic strain Tectonic earthquakes occur anywhere in maximum earthquake magnitude on a fault is however not the maximum available length, but energy to drive fracture propagation alongaafactor of 20. Along sides of a fault move past each other fault plane. The the available width because the latter varies by smoothly and aseismically dip angle of the rupture plane is very or asperities along the fault surface converging plate margins, the only if there are no irregularities that increase theabout 10 degrees.[6] Thus the width of the plane have such asperities and this leads to shallow, typically frictional resistance. Most fault surfaces do a formthe top brittle crust of the Earth can become hasto 100 kmcontinued relative motion between the within of stick-slip behaviour. Once the fault 50 locked, (Japan, 2011; Alaska, 1964), making the most powerful earthquakes plates leads to increasing stress and therefore, stored strain energy in the volume around the fault possible. This continues until the stress has risen sufficiently to break through the asperity, surface. Strike-slip allowing sliding over the locked portion of the fault, releasing the stored energy. This resulting in an suddenly faults tend to be oriented near vertically, [7] approximate width of 10 km within the brittle crust, elastic strain seismic waves, frictional heating of energy is released as a combination of radiated thus earthquakes with magnitudes much larger than 8 are not possible. Maximum the fault surface,many cracking of the rock,more limited because and normal faults are even thus causing an earthquake. This process of gradual magnitudes along build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as many of them are located along spreading centers, as in Iceland, where the thickness of the brittle layer is only about 6that [8][9] 10 percent or less of an earthquake's total the elastic-rebound theory. It is estimated km. only energy is radiated as seismic energy. Most ofin the three fault energy is used to power the In addition, there exists a hierarchy of stress level the earthquake's types. Thrust faults are generated is the highest, strike slip by earthquake fracture growth or by converted into heat generated by friction. Therefore, earthquakes intermediate, and normal faults by the lowest stress levels.[10] raise its lower the Earth's available elastic potential energy and This can temperature, though these easily be understood by considering the direction of the greatest changes are negligible compared to the conductive and convective flow of heat out from the principal stress, the direction of the force that 'pushes' the rock mass Earth's deep interior.[2] during the faulting. In the case of normal faults, the rock mass is pushed down in a vertical direction, thus the pushing force (greatest principal stress) equals the weight of the rock mass itself. In the case of thrusting,
    • EARTHQUAKES AWAY FROM PLATE BOUNDARIES Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain Main article: Intraplate earthquake energy plate boundaries propagation along a fault lithosphere,sides of a fault move past each other Where to drive fracture occur within continental plane. The deformation is spread out smoothly and aseismically only if there are no irregularities or asperitiesSan Andreas fault over a much larger area than the plate boundary itself. In the case of the along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to continental transform, many earthquakes occur away from the plate boundary and are a form of stick-slip behaviour. Once the fault has locked, continued caused by majorbetween the related to strains developed within the broader zone of deformation relative motion plates leads to increasingtrace (e.g., the "Big bend" region).energy in the volume around the fault irregularities in the fault stress and therefore, stored strain The Northridge earthquake surface. This continues until theon a blind thrust sufficiently to zone. Another example is was associated with movement stress has risen within such a break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This the strongly oblique convergent plate boundary between the Arabian and Eurasian plates energyit runs throughathe northwesternradiatedthe Zagros mountains.waves, frictional heating of where is released as combination of part of elastic strain seismic The deformation the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual associated with this plate boundary is partitioned into nearly pure thrust sense movements build-up of strainthe boundary over a wide zone to the sudden earthquake failure is referred to as perpendicular to and stress punctuated by occasional southwest and nearly pure strikethe elastic-rebound theory. It is estimatedcloseonly 10 percent or boundary itself. This is total slip motion along the Main Recent Fault that to the actual plate less of an earthquake's energy is radiated as seismic focal mechanisms.[11] demonstrated by earthquake energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is stress fields caused by their interactions with All tectonic plates have internal converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, [12]). These neighbouring plates and sedimentary loading or unloading (e.g. deglaciation though these changes maynegligible compared tofailure along existing fault planes, giving rise to from the stresses are be sufficient to cause the conductive and convective flow of heat out Earth's deep interior.[2][13] intraplate earthquakes.
    • SHALLOW-FOCUS AND DEEPFOCUS EARTHQUAKES The pointearthquakes occur anywhere in the earth earth there is sufficient stored elastic strain Tectonic of disturbance below the surface of the where is called Focus. fracture propagation along a fault plane. The sides of a fault move past each other energy to drive The majority of tectonic earthquakes originate at the ring of fire in depths notare no irregularities or asperities along the fault surface smoothly and aseismically only if there exceeding tens of kilometers. Earthquakesresistance. at a depth of less do have such asperities and this leads to that increase the frictional occurring Most fault surfaces than 70of stick-slip behaviour. Once the fault has locked, continued relative motion between the a form km are classified as 'shallow-focus' earthquakes,to increasing with a and therefore, stored 70 energy in the volume around the fault plates leads while those stress focal-depth between strain and 300 Thisare commonly termed 'mid-focus' or surface. km continues until the stress has risen sufficiently to break through the asperity, 'intermediate-depth' earthquakes. Inlocked portion of the fault, releasing the stored energy. This suddenly allowing sliding over the subduction zones, where older and coldercombination of radiated beneathstrain seismic waves, frictional heating of energy is released as a oceanic crust descends elastic another tectonic plate, deep-focusthe rock, thusmay the fault surface, and cracking of earthquakes causing an earthquake. This process of gradual occur at much greater stress punctuated by occasional sudden earthquake failure is referred to as build-up of strain and depths (ranging from 300 up to [14] 700elastic-rebound theory.seismically active areas of percent or less of an earthquake's total the kilometers). These It is estimated that only 10 subduction are known as Wadati-Benioff zones. Deepenergy is radiated as seismic energy. Most of the earthquake's energy is used to power the focus earthquakes occur at a depth where the subducted earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lithosphere should no longer be brittle, due energyhigh raise its temperature, though these lower the Earth's available elastic potential to the and temperature negligible compared to the conductive and convective flow of heat out from the changes are and pressure. A possible mechanism for the generation ofinterior.[2] earthquakes is faulting caused Earth's deep deep-focus by olivine undergoing a phase transition into a spinel structure.[
    • EARTHQUAKES AND VOLCANIC ACTIVITY Earthquakes often occur in anywhere in the and are caused there, both by stored elastic and the Tectonic earthquakes occur volcanic regions earth where there is sufficient tectonic faultsstrain movement of magma in volcanoes. along a fault plane. The sides an early move past each other energy to drive fracture propagationSuch earthquakes can serve as of a faultwarning of volcanic eruptions, as aseismically only if Helens eruption of 1980. or Earthquake swarms can surface smoothly andduring the Mount St. there are no irregularities[16] asperities along the faultserve as markers for the frictional the flowing magma throughout the volcanoes. These and this leads that increasethe location ofresistance. Most fault surfaces do have such asperitiesswarms can be to recorded stick-slip behaviour. tiltmeters (a device that measures ground slope) and between a form ofby seismometers and Once the fault has locked, continued relative motion used as the sensors to predict imminent or and therefore, stored plates leads to increasing stressupcoming eruptions strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.[2]
    • RUPTURE DYNAMICS A tectonic earthquakeoccur anywhere in the earth at a point on is sufficient stored elastic strain Tectonic earthquakes begins by an initial rupture where there the fault surface, a process known as nucleation. The scale of the nucleation a fault plane. The sides of a evidence, such each energy to drive fracture propagation alongzone is uncertain, with some fault move pastas the other rupture dimensions of the smallestthere are no irregularitiesthatasperities along the fault surface smoothly and aseismically only if earthquakes, suggesting or it is smaller than 100 m while other evidence, frictional resistance. Most fault surfaces do have such asperities and that increase thesuch as a slow component revealed by low-frequency spectra of somethis leads to earthquakes, suggest that it is Once The possibility that continued relative motion between a form of stick-slip behaviour.larger. the fault has locked,the nucleation involves some sort ofthe preparation process is supportedand the observation that about 40%in the volume around the fault plates leads to increasing stress by therefore, stored strain energy of earthquakes are preceded by foreshocks. Once the rupture has initiated it sufficiently to break through fault surface. surface. This continues until the stress has risenbegins to propagate along the the asperity, The mechanics of this process are poorly understood, partly because it is difficult to recreate the high suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This sliding velocities as combination of radiated elastic strain seismic waves, frictional heating of energy is releasedin aalaboratory. Also the effects of strong ground motion make it very difficult to record information close to of the rock, zone.[18] the fault surface, and cracking a nucleation thus causing an earthquake. This process of gradual Rupture propagation is generally modeled using a fracture mechanics approach, likening the as build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to rupture to a propagating mixed estimated that only 10 rupture velocity an function of the the elastic-rebound theory. It is mode shear crack. The percent or less ofis a earthquake's total fractureis radiated as seismic energy. Most of the earthquake's energy is used tofracture the energy energy in the volume around the crack tip, increasing with decreasing power energy. The velocity of rupture propagation is orders of magnitude faster friction. Therefore, earthquakes earthquake fracture growth or is converted into heat generated by than the displacement velocity across the fault. available elastic potential energy and raise its temperature, in the these lower the Earth'sEarthquake ruptures typically propagate at velocities that arethough range 70– 90% of the S-wave velocity and thisthe independentandearthquake size. A small subset of the changes are negligible compared to is conductive of convective flow of heat out from earthquake ruptures [2] Earth's deep interior.appear to have propagated at speeds greater than the S-wave velocity. These supershear earthquakes have all been observed during large strike-slip events. The unusually wide zone of coseismic damage caused by the 2001 Kunlun earthquake has been attributed to the effects of the sonic boom developed in such earthquakes. Some earthquake ruptures travel at
    • Tidal forces Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain Research work has shown a robust correlation between small tidally induced forces and non-volcanic tremor energy[19][20][21][22]fracture propagation along a fault plane. The sides of a fault move past each other to drive activity. smoothly and aseismically only if there are no irregularities or asperities along the fault surface Earthquake clusters that increase the frictionalaresistance. Most fault other in terms of location and time.[23] Most earthquake to Most earthquakes form part of sequence, related to each surfaces do have such asperities and this leads clusters of stick-slip tremors that cause the fault has locked, continued relative motion between the a form consist of smallbehaviour. Oncelittle to no damage, but there is a theory that earthquakes can recur in a regular pattern.[24]increasing stress and therefore, stored strain energy in the volume around the fault plates leads to Aftershocks surface. This continues until the stress has risen sufficiently to break through the asperity, Main article: Aftershock suddenly allowing sliding that occurslockedprevious earthquake, the mainshock. the aftershock is in the same An aftershock is an earthquake over the after a portion of the fault, releasing An stored energy. This energy is released as but always of a smaller magnitude. If anstrain seismic waves,the main shock, the of region of the main shock a combination of radiated elastic aftershock is larger than frictional heating aftershock is redesignated as the main shock and the original main an earthquake. This a foreshock. gradual the fault surface, and cracking of the rock, thus causing shock is redesignated as process of Aftershocks [23] are formedof strain and stress punctuated by occasional sudden earthquake failure is referred to as build-up as the crust around the displaced fault plane adjusts to the effects of the main shock. Earthquake swarms the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total Main article: Earthquake swarm energy is radiated as seismic of earthquakes striking in a specific areaenergyais used to power the are Earthquake swarms are sequences energy. Most of the earthquake's within short period of time. They earthquake fracture growth or is convertedaftershocks by the fact that no single earthquake in the sequence is different from earthquakes followed by a series of into heat generated by friction. Therefore, earthquakes obviously the main available elastic have notable higher magnitudes than the other. An example of an lower the Earth'sshock, therefore nonepotential energy and raise its temperature, though these [25] earthquake swarm is the 2004 activity atto the conductive and convective flow of heat out earthquakes changes are negligible compared Yellowstone National Park. In August 2012, a swarm of from the shook Southern California's Imperial Valley, showing the most recorded activity in the area since the 1970s.[26] Earth's deep interior.[2] Earthquake storms Main article: Earthquake storm Sometimes a series of earthquakes occur in a sort of earthquake storm, where the earthquakes strike a fault in clusters, each triggered by the shaking or stress redistribution of the previous earthquakes. Similar to aftershocks but
    • SIZE AND FREQUENCY OF OCCURRENCE Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain It is estimated that around 500,000 earthquakes occur each year, detectable with current instrumentation. About 100,000 of these can be felt.[29][30] Minor earthquakes occur nearly constantly around the world in energy to drive fracture propagation along a fault plane. The sides of a fault move past each other places like California and Alaska in the U.S., as well as in Mexico, Guatemala, Chile, Peru, Indonesia, Iran, smoothly and aseismically only if there are no irregularities or India and Japan, but earthquakes can Pakistan, the Azores in Portugal, Turkey, New Zealand, Greece, Italy, asperities along the fault surface that increase the frictional resistance. Most fault surfacesAustralia.[31] Larger earthquakesthis leads to occur almost anywhere, including New York City, London, and do have such asperities and occur less a form of stick-slip behaviour.exponential; for example, roughly ten times as many earthquakes larger frequently, the relationship being Once the fault has locked, continued relative motion between the plates leads to 4 occur in a particular time period than earthquakes larger than magnitude 5. In the the fault than magnitude increasing stress and therefore, stored strain energy in the volume around (low seismicity) United Kingdom, for example, has been calculated that break through the asperity, surface. This continues until the stress it hasrisen sufficiently tothe average recurrences are: an earthquakeallowing slidingyear, an earthquakeportion of every 10 years, and an earthquake of 5.6 or larger suddenly of 3.7–4.6 every over the locked of 4.7–5.5 the fault, releasing the stored energy. This every 100 years.[32] Thisais an example of the Gutenberg–Richter law. energy is released as combination of radiated elastic strain seismic waves, frictional heating of The number of seismic stations has increased from about 350 in 1931 to many thousands today. As a result, the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual many more earthquakes are reported than in the past, but this is because of the vast improvement in build-up of strain and stress increase in the number of earthquakes.earthquake States Geological Survey instrumentation, rather than an punctuated by occasional sudden The United failure is referred to as the elastic-rebound theory. It have been an average of 18 major earthquakes (magnitude 7.0–7.9) and one estimates that, since 1900, there is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most year, and that this average has is used to power the[34] In great earthquake (magnitude 8.0 or greater) per of the earthquake's energy been relatively stable. earthquake fracture growth or is converted into heat generated by friction.isTherefore, statistical recent years, the number of major earthquakes per year has decreased, though this probably a earthquakes fluctuation rather than a systematic trend.[citation energy and raise statistics on the size and frequency lower the Earth's available elastic potentialneeded] More detailed its temperature, though these of [35] earthquakes isnegligible compared to the conductive and convective flow of heat out from the changes are available from the United States Geological Survey (USGS). A recent increase in the number of major earthquakes has been noted, which could be explained by a cyclical pattern of periods of Earth's deep interior.[2] intense tectonic activity, interspersed with longer periods of low-intensity. However, accurate recordings of earthquakes only began in the early 1900s, so it is too early to categorically state that this is the case. [36] Most of the world's earthquakes (90%, and 81% of the largest) take place in the 40,000 km long, horseshoe-
    • SEISMOGRAPH An instrument for automatically detecting and recording there is sufficient storedand duration of a Tectonic earthquakes occur anywhere in the earth where the intensity, direction, elastic strain movement of the ground, especially of an earthquake. Seismometers are instruments that measure energy to drive fracture propagation along a fault plane. The sides of a fault move past each other motions of theaseismically only ifthose of seismic waves generated by earthquakes,fault surface smoothly and ground, including there are no irregularities or asperities along the volcanic eruptions, and other seismic sources. Records of surfaces waves allow seismologists to map the to that increase the frictional resistance. Most fault seismic do have such asperities and this leads interiorof stick-slip behaviour. Oncemeasure the size of these different sources. a form of the Earth, and locate and the fault has locked, continued relative motion between the The word derives from the Greek σεισμός, seismós, astrain energy in the from the around the fault plates leads to increasing stress and therefore, stored shaking or quake, volume verb σείω, seíō, to shake; and continues until the stress has risen coined by David Milne-Home in asperity, surface. This μέτρον, métron, measure and was sufficiently to break through the 1841, to describe an instrument designed bylocked portion of the fault, releasing the[1] suddenly allowing sliding over the Scottish physicist James David Forbes. stored energy. This Seismograph is another Greek term from seismós and γράυω, gráphō, to draw. It is often usedof energy is released as a combination of radiated elastic strain seismic waves, frictional heating to mean seismometer, though it isof the rock, thus causing an earthquake. Thiswhich the measuring the fault surface, and cracking more applicable to the older instruments in process of gradual and recording of ground motion were combined than to modern systems, in which these functions build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as are separated. Both theory. It is estimated that only 10 of ground motion;an earthquake's total the elastic-rebound types provide a continuous record percent or less of this distinguishes them from seismoscopes, which merely indicate of the earthquake's energy perhapsto power the energy is radiated as seismic energy. Most that motion has occurred, is used with some simple [2] measure of fracture growth or is converted into heat generated by friction. Therefore, earthquakes earthquake how large it was. The concerning technical discipline is called seismometry,[3] itsbranch of seismology.these lower the Earth's available elastic potential energy and raise a temperature, though changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.[2]
    • MEASURING AND LOCATING EARTHQUAKESfault move past each other Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a Earthquakes can be recorded by seismometers up to great distances, because seismic waves travel through the whole Earth's interior. The absolute magnitude of a quake is conventionally reported by numbers on the Moment magnitude scale (formerly Richter scale, magnitude 7 causing serious damage over large areas), smoothly and aseismically reported there are modified Mercalli intensity scale along the II–XII). whereas the felt magnitude is only if using the no irregularities or asperities (intensity fault surface that increaseproduces different types of seismic fault surfacestravel through rock with different velocities: Every tremor the frictional resistance. Most waves, which do have such asperities and this leads to Longitudinal P-waves (shock- or Once waves) a form of stick-slip behaviour.pressurethe fault has locked, continued relative motion between the Transverse S-waves (both body waves) therefore, stored strain energy in the volume around the fault plates leads to increasing stress and Surface waves — (Rayleigh and the stress has risen sufficiently to break through the asperity, surface. This continues until Love waves) Propagation velocity sliding over the locked portionapprox. 3 km/sreleasing the stored energy. This suddenly allowing of the seismic waves ranges from of the fault, up to 13 km/s, depending on the density and elasticity of the medium. In the Earth's interior the shock- or P waves travel much faster than the energy is released as a combination of radiated elastic strain seismic waves, frictional heating of S waves (approx. relation 1.7 : 1). The differences in travel time from the epicentre to the observatory are a the faultof the distance and can beof theto image both sources an quakes and structures within of gradual measure surface, and cracking used rock, thus causing of earthquake. This process the Earth. build-updepth of the hypocenter can be computed roughly. sudden earthquake failure is referred to as Also the of strain and stress punctuated by occasional the elastic-rebound theory. It is estimated thatsecond; the velocity increasesan earthquake's total to In solid rock P-waves travel at about 6 to 7 km per only 10 percent or less of within the deep mantle ~13 km/s. radiated as of S-waves ranges from 2–3 km/s in light sediments and 4–5 km/s in the the energy is The velocity seismic energy. Most of the earthquake's energy is used to power Earth's crust up to 7 km/s fracture growth or isaconverted into heat generatedaby friction. Therefore, earthquakes earthquake in the deep mantle. As consequence, the first waves of distant earthquake arrive at an observatory via the available elastic potential energy and raise its temperature, though these lower the Earth's Earth's mantle. On average, the kilometercompared to the conductive and convective flow of heat out and S wave changes are negligible distance to the earthquake is the number of seconds between the P from the times 8.[44] Slight deviations are caused by inhomogeneities of subsurface structure. By such analyses of Earth's deep interior.[2] seismograms the Earth's core was located in 1913 by Beno Gutenberg. Earthquakes are not only categorized by their magnitude but also by the place where they occur. The world is divided into 754 Flinn–Engdahl regions (F-E regions), which are based on political and geographical
    • EFFECTS OF EARTHQUAKES Tectonic earthquakes occur anywhereof earthquakes include, but sufficient stored elastic strain The effects in the earth where there is are not energy to drive fracture propagation along a fault plane. The sides of a fault move past each other limited to, the following: smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behaviour. Once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault surface. This continues until the stress has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This Shaking and ground rupture are the main effects created by earthquakes, principally resulting in energy is released as a combination of radiated elastic strain seismic waves, frictional heating of more or less severe damage to of the rock, thus causing an earthquake. This process of local the fault surface, and cracking buildings and other rigid structures. The severity of the gradual effects depends on thestress punctuated by occasional sudden earthquake failure is referred tothe build-up of strain and complex combination of the earthquake magnitude, the distance from as epicenter, and the local geological and geomorphological conditions, of an earthquake's total the elastic-rebound theory. It is estimated that only 10 percent or less which may amplify or reduce wave propagation.[46] The ground-shakingearthquake's energy is used to power the energy is radiated as seismic energy. Most of the is measured by ground acceleration. Specific local geological, geomorphological, and geostructural by friction. Therefore, earthquakes earthquake fracture growth or is converted into heat generated features can induce high levels of shaking on the ground surface even from low-intensity raise its temperature, though these or lower the Earth's available elastic potential energy and earthquakes. This effect is called site local amplification. It is principally due conductive andof the seismic motion from hard deep soils changes are negligible compared to the to the transfer convective flow of heat out from the to soft superficial soils and to effects of seismic energy focalization owing to typical geometrical Earth's deep interior.[2] setting of the deposits. Ground rupture is a visible breaking and displacement of the Earth's surface along the trace of the fault, which may be of the order of several metres in the case of major earthquakes. Ground Shaking and ground rupture
    • Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface Main article: Landslide that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to Earthquakes, along with severe storms, fault has locked, continued relative motion between the a form of stick-slip behaviour. Once thevolcanic activity, coastal wave attack, and wildfires, can produce slope instability leading to landslides,stored strain energy hazard. Landslide danger may plates leads to increasing stress and therefore, a major geological in the volume around the fault persist while continues until the stress attempting rescue. surface. This emergency personnel are has risen sufficiently to break through the asperity, suddenly allowing sliding over the locked portion of the fault, releasing the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of Fires of the 1906 and cracking of the rock, thus causing an earthquake. This process of gradual the fault surface, San Francisco earthquake Earthquakes can causestress by damaging electrical power or gas lines. In failure is referred to as build-up of strain and fires punctuated by occasional sudden earthquake the event of water mains rupturing andtheory. of is estimatedmay also become difficult toof an earthquake's total the elastic-rebound a loss It pressure, it that only 10 percent or less stop the spread of a fire once it has started.as seismic energy. Most of thethe 1906 San Franciscoused to power thecaused energy is radiated For example, more deaths in earthquake's energy is earthquake were [49] by fire than fractureearthquake is converted into heat generated by friction. Therefore, earthquakes earthquake by the growth or itself. lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Main article: Soil liquefaction Earth's deep interior.[2] Soil liquefaction occurs when, because of the shaking, water-saturated granular material (such as sand) temporarily loses its strength and transforms from a solid to a liquid. Soil liquefaction may cause rigid structures, like buildings and bridges, to tilt or sink into the liquefied deposits. For Landslides and avalanches Fires Soil liquefaction
    • Tsunami Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other Tsunamis and long-wavelength, long-period no irregularities or asperities along theabruptsurface smoothly are aseismically only if there are sea waves produced by the sudden or fault movement ofthe frictional resistance. Most fault surfaces dodistance between wave crests leads to that increase large volumes of water. In the open ocean the have such asperities and this can surpassof stick-slip behaviour. Once the wave has locked, continued relative motion between the a form 100 kilometers (62 mi), and the fault periods can vary from five minutes to one hour. Such tsunamis increasing stress and therefore,hour (373–497 miles in the volume around on water plates leads to travel 600-800 kilometers per stored strain energy per hour), depending the fault depth. Large waves producedthe stress has risen or a submarine break through overrun nearby surface. This continues until by an earthquake sufficiently to landslide can the asperity, coastal areas in a matter ofover the locked portion of the fault,thousands thekilometers across open suddenly allowing sliding minutes. Tsunamis can also travel releasing of stored energy. This [51] ocean andreleaseddestruction on far shores hours after the earthquakewaves, frictional heating of energy is wreak as a combination of radiated elastic strain seismic that generated them. Ordinarily, subduction earthquakes under magnitude 7.5an earthquake. This process cause the fault surface, and cracking of the rock, thus causing on the Richter scale do not of gradual tsunamis,of strain and stress punctuated byhave been recorded.earthquake failuretsunamis are as build-up although some instances of this occasional sudden Most destructive is referred to caused by earthquakes of magnitude 7.5 or more 10 percent or less of an earthquake's total the elastic-rebound theory. It is estimated that only energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.[2]
    • Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain energy to drive fracture propagation along a fault plane. The sides of a fault move past each other smoothly and aseismically only if there are no irregularities or asperities along the fault surface that increase the frictional resistance. Most fault surfaces do have such asperities and this leads to a form of stick-slip behaviour. Once the fault has locked, continued relative motion between the plates leads to increasing stress and therefore, stored strain energy in the volume around the fault A flood is an overflow of any amount of water that reaches land.[52] Floods occur usually when surface. This continues until the stresswater, such as a river or lake, exceeds the total capacity of the volume of water within a body of has risen sufficiently to break through the asperity, suddenly allowing as a result some lockedwater flows or fault, releasingthe normal energy. This the formation, and sliding over the of the portion of the sits outside of the stored perimeter of energy is released asfloods may be secondary effects ofstrain seismic if damsfrictional heating of the body. However, a combination of radiated elastic earthquakes, waves, are damaged. the fault surface, and cracking of thedam rivers, causing an earthquake. This process of gradual Earthquakes may cause landslips to rock, thus which collapse and cause floods.[53] build-up of below and Sarez Lake in Tajikistan is in danger of catastrophicfailure if the landslide The terrain strain the stress punctuated by occasional sudden earthquake flood is referred to as the elastic-rebound earthquake, estimated thatUsoi Dam, were or less duringearthquake's total dam formed by the theory. It is known as the only 10 percent to fail of an a future earthquake. energy is radiated as seismic energy. Most of the earthquake's energy is used to power the Impact projections suggest the flood could affect roughly 5 million people.[54] earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.[2] Floods
    • PREDICTION Many methods have been developed for predicting the time and place in which earthquakes will Tectonic earthquakes occur anywhere in the earth where there is sufficient stored elastic strain occur. Despite considerable research along a by seismologists, scientifically reproducible energy to drive fracture propagation efforts fault plane. The sides of a fault move past each other [60] predictions cannot yet be made to a specificno irregularities orHowever, for well-understood smoothly and aseismically only if there are day or month. asperities along the fault surface faults the probability that aresistance. Most fault surfacesthe next few decades canand this leads to segment may rupture during do have such asperities be that increase the frictional [61] estimated.stick-slip behaviour. Once the fault has locked, continued relative motion between the a form of Earthquake warning systems have been developed that can energy in the volume around thean plates leads to increasing stress and therefore, stored strain provide regional notification of fault earthquake incontinues until the stress ground surface has begun to move, potentially allowing surface. This progress, but before the has risen sufficiently to break through the asperity, people within the system's over the locked portion of the fault, releasing impact is felt. suddenly allowing sliding range to seek shelter before the earthquake's the stored energy. This energy is released as a combination of radiated elastic strain seismic waves, frictional heating of the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.[2]
    • BHUJ EARTHQUAKE The 2001 Gujarat earthquake (bhuj in the earth where there is sufficient stored elastic strain Tectonic earthquakes occur anywhere earthquake)occurred on January 26, 2001, India's 52nd Republic drive fracture propagation along a UTC) and lasted for over fault move past each other energy to Day, at 08:46 AM local time (3:16 fault plane. The sides of atwo minutes. The epicentre was about 9 km south-southwest there are no of Chobari[3] in Bhachau along of fault District smoothly and aseismically only ifof the village irregularities or asperitiesTalukathe Kutchsurface of Gujarat, India.[4] The earthquake reached a magnitude do have such asperities and this leads that increase the frictional resistance. Most fault surfaces of between 7.6 and 7.7 on the momentto magnitude scale and had a maximum felt intensity of X (Intense) on the Mercalli intensity scale. a form of stick-slip behaviour. Once the fault has locked, continued relative motion between the The quake to increasing stress people (including 18 in South eastern Pakistan), injured another plates leadskilled around 20,000and therefore, stored strain energy in the volume around the fault 167,000 and continues until the stress homes.[5] surface. This destroyed nearly 400,000 has risen sufficiently to break through the asperity, This was allowing sliding over the locked occurred the distance from the stored energy. This suddenly an intraplate earthquake, one thatportion of at a fault, releasingan active plate boundary, so the is released as a combination of shock waves spread 700 km. waves, frictional heating and energyarea was not well prepared. The radiated elastic strain seismic 21 districts were affected of 600,000 surface, and cracking the fault people left homeless. of the rock, thus causing an earthquake. This process of gradual build-up of strain and stress punctuated by occasional sudden earthquake failure is referred to as the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.[2]
    • EFFECTS The final death toll in Kutch was 12,300. Bhuj, situated only 20 kilometres (12 mi) from elastic strain Tectonic earthquakes occur anywhere in the earth where there is sufficient stored the epicenter, was devastated. Considerable damage also occurred in Bhachau and Anjar with hundreds of villages energy to drive fracture propagation along a fault plane. The sides of a fault move past each other flattened in Taluka of Anjar, Bhuj & Bhachau. Over a million structures were damaged or destroyed, smoothlymanyaseismically onlyandthere are no irregularities or asperities along the fault surface and historic buildings if tourist attractions.[7] The quake destroyed around 40% of homes, including that increase the frictionaland 4 km of road infault surfaces do have such asperities and this leads to eight schools, two hospitals resistance. Most Bhuj and partly destroyed the city's historic a form of stick-slip behaviour. Once as well Prag Mahal andcontinued relative motion between the Swaminarayan temple and historic fort the fault has locked, Aina Mahal. In Ahmedabad, Gujarat's plates leadscapital with a population of 5.6 million, as many as 50 multi-storied buildings collapsedfault commercial to increasing stress and therefore, stored strain energy in the volume around the and surface. This continues until the stress property damage was estimated at $5.5 billionasperity, In several hundred people were killed. Total has risen sufficiently to break through the and rising. Kutch, the quake destroyed over the of food and water the fault, releasing the stored energy. This suddenly allowing slidingabout 60%locked portion of supplies and around 258,000 houses - 90% of the district's housingas a combination of radiated elastic strain seismic waves, frictional heating of energy is released stock. The biggest set back was the total demolition of the Bhuj Civil hospital. The Indian military provided emergency the rock, thus was later an earthquake. This process of gradual of the fault surface, and cracking of support which causing augmented by the International Federation Red Crossof strain and stress punctuated by occasional sudden earthquake failure is referred care build-up and Red Crescent Society. A temporary Red Cross hospital remained in Bhuj to provide to as while a replacement hospital was built.[8] the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total Relief poured in from all over the world and over a longer period of time, the affected area was reenergy is radiated as seismic energy. Most of the earthquake's energy is used to power the equipped with all the basic facilities along with state-of-the-art upgrades. The result being that Bhuj, along earthquake fracture growth villages, is now complete with a better by friction. Therefore, earthquakes or is converted into heat generated hospital, town and first-aid center. with several small towns and lowerseveral guidelines and rules were put intoenergy and raise its government for real-estate and Also, the Earth's available elastic potential place by the Gujarat temperature, though these changes are businesses in foresight of another such event. Aconvective flow of heat out from the construction negligible compared to the conductive and rather amusing piece of trivia that happened Earth's deep interior.[2] the quake, India had shot down a Pakistani fighter aircraft for alleged violation was, a few months before of its air-space. So when the turn came for Pakistan to send a relief aircraft full with aid and goods, a rather global announcement was made in order to safe-guard it and avoid any such repetition. Another interesting event that occurred was the emergence of a river in the dry land of Kutch that ran
    • TECTONIC SETTING Gujarat lies about 400occur anywhere in the earth where there isIndian Plate and the Eurasian Tectonic earthquakes km from the plate boundary between the sufficient stored elastic strain Plate, but the current tectonics is still governed by the effects of the continuing continental energy to drive fracture propagation along a fault plane. The sides of a fault move past each other collision along this boundary. During the break-up of Gondwana in the Jurassic, this area was smoothly and aseismically only if there are no irregularities or asperities along the fault surface affected by rifting with a roughly west-east trend. During the collision asperities and this leads that increase the frictional resistance. Most fault surfaces do have such with Eurasia the area hasto undergone shortening, involving both reactivation of the continued relative motion between of a form of stick-slip behaviour. Once the fault has locked, original rift faults and development the new low-angleincreasing stress and therefore, storedformedenergy inof ranges, particularly infault plates leads to thrust faults. The related folding has strain a series the volume around the central This continues until the stress most earthquakes is to break through the asperity, surface.Kutch. The focal mechanism ofhas risen sufficiently consistent with reverse faulting on reactivated rift faults. The over theof uplift portion of the fault, releasing the stored energy.of suddenly allowing sliding pattern locked and subsidence associated with the 1819 Rann This Kutch is released as a combination reactivation of such a fault. The waves, frictional heating was energyearthquake is consistent with of radiated elastic strain seismic 2001 Gujarat earthquake of caused by movement on a previously unknown south-dipping fault, trending parallel to the the fault surface, and cracking of the rock, thus causing an earthquake. This process of gradual inferred rift strain and stress punctuated by occasional sudden earthquake failure is referred to as build-up of structures.[ the elastic-rebound theory. It is estimated that only 10 percent or less of an earthquake's total energy is radiated as seismic energy. Most of the earthquake's energy is used to power the earthquake fracture growth or is converted into heat generated by friction. Therefore, earthquakes lower the Earth's available elastic potential energy and raise its temperature, though these changes are negligible compared to the conductive and convective flow of heat out from the Earth's deep interior.[2]