Earthquakes can be caused by many factors, therefore, the types
of earthquakes are also diversiform, but divided into five categories
usually: tectonic earthquake, volcanic earthquake, collapse
earthquake, induced earthquake and artificial earthquake.
Tectonic earthquake，under the action of tectonic movement，when
the crustal stress reach even exceed the ultimate strength of the
rock stratum, the rock stratum will suddenly deform, and even
rupture, release the energy at once, then result the ground shake.
Tectonic earthquake is the earthquake caused by the dislocation and
fracture of the deep underground rock stratum. In the earthquakes
of all over the world, more than 90 percent are tectonic earthquakes.
Tectonic earthquakes are most destructive, impact on a wider scope.
After the volcanic earthquake and volcanic eruption, due to massive
magmatic losses, the underground pressure decreases or the subsurface
magma are too late to replenish, a hollow happens. Volcanic earthquakes
are only possible to occur in volcanic activity areas, volcanic earthquakes
are rare. Modern volcanic belts such as Italy, Japan, the Philippines
and Indonesia, they are more prone to occur the volcanic earthquakes.
Falling earthquakes are the local earthquake that due to the underground
caverns or the subsidence of the mine goaf. Falling earthquakes are the
result of gravity, small scale, fewer times. In 1935, there was a collapse
earthquake in Baishou County Guangxi Procince, the collapse area is about
40000 m2, the ground fell into deep pools, sounds can be heard dozens of miles,
roof tiles vibrated nearby. In March 1972, large areas of roof collapse caused
the earthquake in western Datong coal goaf in Shanxi, which maximum magnitude
is 3.4, the buildings in the central area were slightly damaged.
Induced earthquakes caused by the activities, such as reservoirs storage and
oilfield water injection. Due to the increasing of reservoir storage, result
in uneven stress distribution and local pressure buildup, as a result, the rock
stratum cannot bear external additional pressure, rupture、dislocation occurs,
then earthquake occurs. Such as China's Xinfengjiang reservoir、Danjiangkou
reservoir, there have been medium and small earthquakes in the two regions.
Among them, the largest magnitude was the Xinfengjiang reservoir in 1962,
reached at 6.1 magnitude.
Man-made ground vibrations about artificial earthquake underground nuclear
explosion、explosive blasting etc.
Earthquake classification can also be divided into the following aspects.
(1)Classified according to the focal depth.
Shallow-focus earthquake: the focal depth is less than 70km:
Intermediate-focus earthquake: the focal l depth is l70km-300km:
Palintectic earthquake: the focal l depth is more than 300km.
90 percent of all earthquakes have the focal depth of less than 100km in
the world, only 3% of earthquakes are palintectic earthquake.
(2)Classified by the magnitude of the earthquakes
Microseismic earthquake: magnitude 1＜magnitude＜magnitude 3:
Minor earthquake: magnitude 3＜magnitude＜magnitude 4.5:
Moderate earthquake: magnitude 4.5＜magnitude＜magnitude 6:
Strong earthquake: magnitude 6＜magnitude＜magnitude 7:
Major earthquake: magnitude＞magnitude 7:
Huge earthquake: magnitude＞magnitude 8:
Felt earthquake: the earthquake that can be felt near the epicenter:
Destructive earthquake: the earthquake that causes casualties and economic damage：
Severely destructive earthquake: cause the seriously loss of casualties
and properties, make the disaster area lose or partially lose its
ability to recover.
Local earthquakes are classified according to the size of epicentral
distance: the epicenter was less than 100km:
Near earthquake: the epicenter100-1000km:
Distant earthquake: the epicenter﹥1000km.