Causes the Earth surface layer vibration reason to be very many,according to the earthquake origin, may divide into the earthquakefollowing several kinds:
1. tectonic earthquakes
Because the underground deep place rock layer moves out ofplace the earthquake which, bursts creates to be called the tectonicearthquake (chart 1 - 1). This kind of earthquake occurs number oftimes most, the destructive power is also biggest, approximatelycomposes above world earthquake 90%.
2. volcanic earthquakes
As a result of the volcanism, like the magmatic activity, thegaseous detonation and so on the earthquake which causes is called thevolcanic earthquake. Only has in the volcanic activity area only thenpossibly has the volcanic earthquake, this kind of earthquake onlyoccupies the world earthquake about 7%.
3. caves in the earthquake
Because the underground grotto or the mine pit crown cave inthe earthquake which causes to be called caves in the earthquake. Thiskind of earthquake scale quite small, the number of times very arealso few, even if has, also often occurs in the limestone cave denselycovered limestone area or the large-scale underground mining miningarea.
4. induces the earthquake
Because the reservoir stores water, the oil field pours waterthe earthquake which and so on the activity initiates to be calledinduces the earthquake. This kind of earthquake merely in certainspecific reservoir storehouse districts or oil field area occurrence.
5. artificial earthquakes
The underground nuclear explosion, the blasting explosivedemolition and so on artificial cause the ground vibration is calledthe artificial earthquake. The artificial earthquake is an earthquakewhich causes by the artificial activity. If the industry demolition,the underground nuclear explosion create vibration; Carried onhigh-pressure waterflood as well as the big reservoir after the deepwell stores water increased the earth's crust pressure, sometimes alsocould induce the earthquake.
The earthquake wave originates the place, is called center of origin.Center of origin in the ground vertical projection, is called theepicenter. Is called the depth of origin the epicenter to the centerof origin depth. Usually is smaller than 70 kilometers the depth oforigin to call the shallow source earthquake, the depth to call thesource earthquake, the depth in 70-300 kilometer to be bigger than 300kilometers to call the deep source earthquake. The ruinous earthquakegenerally is the shallow source earthquake. If 1976 Tangshanearthquake depth of origin was 12 kilometers.
