About earthquakes

      world of physical Geography

  What is plate Tectonics？
In order to explain the phenomenon of continental drift and developed a kind of geology theory. The theory is that, the earth's lithosphere is by plate split and become; The global is divided into 6 parts, Marine and land position is changing. According to this theory, the internal structure of the earth the most outer layer is divided into two parts: the outer layer of the lithosphere and intimal asthenosphere. This theory is based on two independent geological observation results: submarine expansion and continental drift.

What are the different types of Plate movements?

---Constructive Plate Movement

l  The plates move away from each other

l  Magma rises to the surface through the gap

l  This will cool down and form new crust (thus constructive plate movement).

---Destructive Plate Movement

l  2 plates move towards each other

l  One plate is forced to subduct (dips/sinks) below the other.

l  The plate that is forced to subduct gets destroyed in the mantle（thus destructive plate movement）.

---Conservative Plate Movement

l  2 plates slide past each other.

l  No crust is created or destroyed.

What are the causes/types of earthquakes?

1.Tectonic earthquake
Due to crustal movement caused by crustal rock fracture movement and happen crustal shock, known as the tectonic earthquake. The result of the earth keep movement change, and within the crust from the tremendous stress effect. In the ground stress under the action of long-term slow, resulting in crustal rock happen bending deformation, the local stress more than rock itself can bear strength would make fracturation movement, its huge energy suddenly release, form tectonic earthquake, earthquake experts usually use elastic rebound theory to describe this phenomenon. The vast majority of the earthquake in the world belong to tectonic earthquake.






2.Volcanic earthquake
Due to the volcanic activities magma eruption impact or thermal effect caused by the earthquake, called volcanic earthquake. Volcanic earthquake generally small, the number of accounts for about 7% of the total number of earthquake. Earthquakes and volcanic often exist in the association. Volcanic eruptions may trigger earthquakes, and happened in volcanic nearby earthquake can also cause volcanic eruption. Generally the impact is not big













3.Collapse earthquake
Due to the water dissolved soluble rocks, or due to underground mining formation of huge hole, causing formation collapse collapse caused by earthquake, called collapse earthquake. This kind of earthquake accounts for about 3% of the total number of earthquake left and right sides, magnitude are relatively small.


4.Induced earthquake
In special areas for some crust induced by external factors caused by the earthquake, called induced earthquake. These external factors can be underground nuclear explosion, meteorite fall, oil well irrigation, etc., one of the most common is reservoir earthquake. Reservoir impounding changed the ground stress state, and the reservoir water infiltration to the existing fault, which has a lubrication and corrosion function, and impel the fault produces sliding. However, not all reservoir impounding can happen reservoir earthquake, only when the existence of active faults, lithology hard conditions, just have the possibility of induced.



Reference:http://zh.wikipedia.org/wiki/%E5%9C%B0%E9%9C%87