What is earthquake?10marks!!!!!

What is earthquake?
An earthquake is the result of a sudden release of energy in the Earth's crust that creates seismic waves. Earthquakes are recorded with a seismometer, also known as a seismograph. The moment magnitude of an earthquake is conventionally reported, or the related and mostly obsolete Richter magnitude, with magnitude 3 or lower earthquakes being mostly imperceptible and magnitude 7 causing serious damage over large areas. Intensity of shaking is measured on the modified Mercalli scale.
About Sichuan
The Sichuan earthquake which measured at 8.0 Ms and 8.3 Mw according to PRC's China Seismological Bureau, and 7.9 Mw according to USGS, occurred at 14:28:01.42 CST on 12 May 2008 in Sichuan. It was also known as the Wenchuan earthquake , after the earthquake's epicenter in Wenchuan County in Sichuan province. The epicenter was 80 kilometres (50 mi) west-northwest of Chengdu, the capital of Sichuan, with a depth of 19 kilometres (12 mi). The earthquake was felt as far away as Beijing (1,500 km away) and Shanghai (1,700 km away), where office buildings swayed with the tremor. The earthquake was also felt in nearby countries.

Official figures (as of June 2, 12:00 CST) state that 69,019 are confirmed dead, including 68,509 in Sichuan province, and 373,573 injured, with 18,627 listed as missing. The earthquake left about 4.8 million people homeless, though the number could be as high as 11 million. It is the deadliest and strongest earthquake to hit China since the 1976 Tangshan earthquake, which killed at least 240,000 people. Approximately 15 million people lived in the affected area.

On May 25, a major aftershock of 6.0 Mw hit northeast of the original earthquake's epicenter, in Qingchuan County, causing eight deaths, 1000 injuries, and destroyed thousands of buildings. On May 27, two more major aftershocks, a 5.2 Mw in Qingchuan County and a 5.7 Mw in Ningqiang in Shaanxi Province, led to the collapse of more than 420,000 homes and injured 63 people.

Earthquakes are the Earth's natural means of releasing stress. When the Earth's plates move against each other, stress is put on the lithosphere. When this stress is great enough, the lithosphere breaks or shifts. Imagine holding a pencil horizontally. If you were to apply a force to both ends of the pencil by pushing down on them, you would see the pencil bend. After enough force was applied, the pencil would break in the middle, releasing the stress you have put on it. The Earth's crust acts in the same way. As the plates move they put forces on themselves and each other. When the force is large enough, the crust is forced to break. When the break occurs, the stress is released as energy which moves through the Earth in the form of waves, which we feel and call an earthquake.
http://scign.jpl.nasa.gov/learn/eq1.htm
Sichuan's Earthquake
The 2008 Sichuan earthquake (Chinese: 四川大地震), or Great Sichuan Earthquake which measured at 8.0 Ms[5] and 8.3 Mw[6] according to PRC's China Seismological Bureau, and 7.9 Mw according to USGS, occurred at 14:28:01.42 CST (06:28:01.42 UTC) on 12 May 2008 in Sichuan province of China. It was also known as the Wenchuan earthquake (Chinese: 汶川大地震), after the earthquake's epicenter in Wenchuan County in Sichuan province. The epicenter was 80 kilometres (50 mi) west-northwest of Chengdu, the capital of Sichuan, with a depth of 19 kilometres (12 mi).[2] The earthquake was felt as far away as Beijing (1,500 km away) and Shanghai (1,700 km away), where office buildings swayed with the tremor.[7] The earthquake was also felt in nearby countries.....................................
and there is a Chinese version about Sichuan's earthquake on the following link
http://en.wikipedia.org/wiki/2008_Sichuan_earthquake