Earthquake Map 'LINK'

At the Earth's surface, earthquakes manifest themselves by shaking and displacing or disrupting 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.

The 1960 Chilean earthquake is the largest earthquake that has been measured on a seismograph, reaching 9.5 magnitude on 22 May 1960.[4][5] Its epicenter was near Caete, Chile. The energy released was approximately twice that of the next most powerful earthquake, the Good Friday earthquake (27 March 1964), which was centered in Prince William Sound, Alaska.[6][7] 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.

Earthquake Map

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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.

Tectonic earthquakes occur anywhere on 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 increases the frictional resistance. Most fault surfaces do have such asperities, which leads to a form of stick-slip behavior. 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.[8] This energy is released as a combination of radiated elastic strain seismic waves,[9] 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.[10]

There are three main types of fault, all of which may cause an interplate earthquake: normal, reverse (thrust), and strike-slip. Normal and reverse faulting are examples of dip-slip, where the displacement along the fault is in the direction of dip and where movement on them involves a vertical component. Many earthquakes are caused by movement on faults that have components of both dip-slip and strike-slip; this is known as oblique slip. The topmost, brittle part of the Earth's crust, and the cool slabs of the tectonic plates that are descending into the hot mantle, are the only parts of our planet that can store elastic energy and release it in fault ruptures. Rocks hotter than about 300 C (572 F) flow in response to stress; they do not rupture in earthquakes.[11][12] The maximum observed lengths of ruptures and mapped faults (which may break in a single rupture) are approximately 1,000 km (620 mi). Examples are the earthquakes in Alaska (1957), Chile (1960), and Sumatra (2004), all in subduction zones. The longest earthquake ruptures on strike-slip faults, like the San Andreas Fault (1857, 1906), the North Anatolian Fault in Turkey (1939), and the Denali Fault in Alaska (2002), are about half to one third as long as the lengths along subducting plate margins, and those along normal faults are even shorter.

Reverse faults occur in areas where the crust is being shortened such as at a convergent boundary. Reverse faults, particularly those along convergent plate boundaries, are associated with the most powerful earthquakes, megathrust earthquakes, including almost all of those of magnitude 8 or more. Megathrust earthquakes are responsible for about 90% of the total seismic moment released worldwide.[15]

Strike-slip faults are steep structures where the two sides of the fault slip horizontally past each other; transform boundaries are a particular type of strike-slip fault. Strike-slip faults, particularly continental transforms, can produce major earthquakes up to about magnitude 8. Strike-slip faults tend to be oriented near vertically, resulting in an approximate width of 10 km (6.2 mi) within the brittle crust.[16] Thus, earthquakes with magnitudes much larger than 8 are not possible.

For every unit increase in magnitude, there is a roughly thirtyfold increase in the energy released. For instance, an earthquake of magnitude 6.0 releases approximately 32 times more energy than a 5.0 magnitude earthquake and a 7.0 magnitude earthquake releases 1,000 times more energy than a 5.0 magnitude earthquake. An 8.6 magnitude earthquake releases the same amount of energy as 10,000 atomic bombs of the size used in World War II.[18]

Earthquakes often occur in volcanic regions and are caused there, both by tectonic faults and the movement of magma in volcanoes. Such earthquakes can serve as an early warning of volcanic eruptions, as during the 1980 eruption of Mount St. Helens.[23] Earthquake swarms can serve as markers for the location of the flowing magma throughout the volcanoes. These swarms can be recorded by seismometers and tiltmeters (a device that measures ground slope) and used as sensors to predict imminent or upcoming eruptions.[24]

A tectonic earthquake begins as an area of initial slip on the fault surface that forms the focus. Once the rupture has been initiated, it begins to propagate away from the focus, spreading out along the fault surface. Lateral propagation will continue until either the rupture reaches a barrier, such as the end of a fault segment, or a region on the fault where there is insufficient stress to allow continued rupture. For larger earthquakes, the depth extent of rupture will be constrained downwards by the brittle-ductile transition zone and upwards by the ground surface. The mechanics of this process are poorly understood because it is difficult either to recreate such rapid movements in a laboratory or to record seismic waves close to a nucleation zone due to strong ground motion.[25]

Supershear earthquake ruptures are known to have propagated at speeds greater than the S-wave velocity. These have so far all been observed during large strike-slip events. The unusually wide zone of damage caused by the 2001 Kunlun earthquake has been attributed to the effects of the sonic boom developed in such earthquakes.

Slow earthquake ruptures travel at unusually low velocities. A particularly dangerous form of slow earthquake is the tsunami earthquake, observed where the relatively low felt intensities, caused by the slow propagation speed of some great earthquakes, fail to alert the population of the neighboring coast, as in the 1896 Sanriku earthquake.[25]

During an earthquake, high temperatures can develop at the fault plane, increasing pore pressure and consequently vaporization of the groundwater already contained within the rock.[27][28][29] In the coseismic phase, such an increase can significantly affect slip evolution and speed, in the post-seismic phase it can control the Aftershock sequence because, after the main event, pore pressure increase slowly propagates into the surrounding fracture network.[30][29]From the point of view of the Mohr-Coulomb strength theory, an increase in fluid pressure reduces the normal stress acting on the fault plane that holds it in place, and fluids can exert a lubricating effect.As thermal overpressurization may provide positive feedback between slip and strength fall at the fault plane, a common opinion is that it may enhance the faulting process instability. After the mainshock, the pressure gradient between the fault plane and the neighboring rock causes a fluid flow that increases pore pressure in the surrounding fracture networks; such an increase may trigger new faulting processes by reactivating adjacent faults, giving rise to aftershocks.[30][29] Analogously, artificial pore pressure increase, by fluid injection in Earth's crust, may induce seismicity.

Most earthquakes form part of a sequence, related to each other in terms of location and time.[31] Most earthquake clusters consist of small tremors that cause little to no damage, but there is a theory that earthquakes can recur in a regular pattern.[32] Earthquake clustering has been observed, for example, in Parkfield, California where a long-term research study is being conducted around the Parkfield earthquake cluster.[33]

An aftershock is an earthquake that occurs after a previous earthquake, the mainshock. Rapid changes of stress between rocks, and the stress from the original earthquake are the main causes of these aftershocks,[34] along with the crust around the ruptured fault plane as it adjusts to the effects of the mainshock.[31] An aftershock is in the same region as the main shock but always of a smaller magnitude, however, they can still be powerful enough to cause even more damage to buildings that were already previously damaged from the mainshock.[34] If an aftershock is larger than the mainshock, the aftershock is redesignated as the mainshock and the original main shock is redesignated as a foreshock. Aftershocks are formed as the crust around the displaced fault plane adjusts to the effects of the mainshock.[31] ff782bc1db