? asked in 科學及數學地理學 · 1 decade ago

about earthquake

information about earthquake !!!!!! QUICK

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information about earthquake !!!!!! QUICK

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  • Tobbit
    Lv 7
    1 decade ago
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    An earthquake is the result of a sudden release of stored energy in the Earth's crust that creates seismic waves. Earthquakes are accordingly measured with a seismometer, commonly known as a seismograph. The magnitude of an earthquake is conventionally reported using the Richter scale or a related Moment scale (with magnitude 3 or lower earthquakes being hard to notice and magnitude 7 causing serious damage over large areas).

    Most naturally occurring earthquakes are related to the tectonic nature of the Earth. Such earthquakes are called tectonic earthquakes. The Earth's lithosphere is a patchwork of plates in slow but constant motion caused by the release to space of the heat in the Earth's mantle and core. The heat causes the rock in the Earth to become flow on geological timescales, so that the plates move slowly but surely. Plate boundaries lock as the plates move past each other, creating frictional stress. When the frictional stress exceeds a critical value, called local strength, a sudden failure occurs. The boundary of tectonic plates along which failure occurs is called the fault plane. When the failure at the fault plane results in a violent displacement of the Earth's crust, the elastic strain energy is released and seismic waves are radiated, thus causing an earthquake. This process of strain, stress, and 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 and is converted into heat, or is released to friction. Therefore, earthquakes lower the Earth's available potential energy and raise its temperature, though these changes are negligible.[1]

    The majority of tectonic earthquakes originate at depths not exceeding tens of kilometers. In subduction zones, where older and colder oceanic crust descends beneath another tectonic plate, Deep focus earthquakes may occur at much greater depths (up to seven hundred kilometers). These seismically active areas of subduction are known as Wadati-Benioff zones. These are earthquakes that occur at a depth at which the subducted lithosphere should no longer be brittle, due to the high temperature and pressure. A possible mechanism for the generation of deep focus earthquakes is faulting caused by olivine undergoing a phase transition into a spinel structure.[2]

    Earthquakes may also occur in volcanic regions and are caused there both by tectonic faults and by the movement of magma in volcanoes. Such earthquakes can be an early warning of volcanic eruptions.

    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, and with some of the later earthquakes as damaging as the early ones. Such a pattern was observed in the sequence of about a dozen earthquakes that struck the North Anatolian Fault in Turkey in the 20th century, the half dozen large earthquakes in New Madrid in 1811-1812, and has been inferred for older anomalous clusters of large earthquakes in the Middle East and in the Mojave Desert.

    Source(s): Wikipedia
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  • 1 decade ago

    information可以分好多方面.唔知你講which one

    http://earthquake.usgs.gov/

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  • 1 decade ago

    地震,就是突然而強烈的震動。當地球內部長期積累起來的地應力(即單位面積上產生的抵抗外力的力)超過岩層所能承受的限度時,岩層便會突然發生斷裂或錯位,使積累的能量急劇地釋放出來,並以波動的震盪形式向四方八面傅播出去,令地面發生震動。

    震動的發源處稱為震源 focus。大多數震源都在地殼和上地幔頂部,即岩石圈內。根據震源的深度,地震可分為三類:淺源地震(深度在0-70公里)、中源地震(深度在70-300公里)和深源地震(深度在300公里以上)。

    由震源豎一垂直線至地面上的位置稱為震中 epicentre。震中是地表距離震源最近的地方,因此地震波最早到達這處,震動也最為強烈,破壞程度也最大。

    地震而產生的波動叫地震波。在地球內部移動的地震波稱為體波,可分為縱波(初波/P波)和橫波(次波/S波)兩種。縱波傳播時,岩石物質振動的方向與傳播的方向一致,而且傳播速度較快;橫波傳播時,岩石物質的振動方向與傳播方向垂直,而且傳播速度較慢。所以,當地震發生時,人們的感覺是先顛後晃。祇能沿地面傳播的地震波稱為面波(L波),是縱波或橫波到達地面後,在一定條件下激發起來的次生波,速度比橫波還慢。一般當橫波或面波到達時,振動最為猛烈,破壞作用也最大。

    地震是地球上極為普遍的自然現象之一。全世界每年大約發生五百萬次地震,平均起來,真是震個不停。幸而,人能夠感覺到的地震祇佔1%左右,能造成傷害的地震更祇是其中的極少數,而災難性的特大地震就更少了。據統計,全世界平均每年發生約18次能造成嚴重破壞的大地震,而特大的地震平均每年祇有一次。

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