4b Group 2 Sichuan Earthquake

Geography Project Sichuan

Earthquake

Member List      

Cheung Chi Lok (4) Chow Siu Yin (5) Yan Kin Chung (20) Fong Wai Sum (24) Ho Mei Ching (25) Kwan Shuk Yee (26)

Earthquake  Earthquakes are the results of earth movement. Rocks of the crust are under great pressure which causes strain to build up.  With continuous tectonic movement the strain may exceed the elastic strength of the rock, so that rock fractures along a fault plane, causing release of the strain and great shaking.

Sichuan a province in western China capital at Chengdu. The area lies in the Sichuan basin and is surrounded by the Himalayas to the west, Qinling range to the north, and mountainous areas of Yunnan to the south.

Sichuan Earthquake Date : 12 May 2008 Time :14:28 – 14:51

Sichuan Earthquake • Earthquake's epicenter :Wenchuan County • Depth of the earthquake focus : 29 km • Richter magnitude scale : 8.0 Ms . • Damage : more than 100,000 square kilometers . • Lasting time : 5 minutes

Cause The earthquake occurred as the result of motion on a northeast striking reverse fault or thrust fault on the northwestern margin of the Sichuan Basin. The earthquake’s epicenter and focal-mechanism are consistent with it having occurred as the result of movement on the Longmenshan fault or a tectonically related fault. The earthquake reflects tectonic stresses resulting from the convergence of crustal material slowly moving from the high Tibetan Plateau, to the west, against strong crust underlying the Sichuan Basin and southeastern China.

Cause On a continental scale, the seismicity of central and eastern Asia is a result of northward convergence of the Indian Plate against the Eurasian Plate with a velocity of about 50 mm/y. The convergence of the two plates is broadly accommodated by the uplift of the Asian highlands and by the motion of crustal material to the east away from the uplifted Tibetan Plateau. The northwestern margin of the Sichuan Basin has previously experienced destructive earthquakes.

Result  Immediate effects Highways and buildings were collapsed. At least 5 million people were homeless.

• Up to May 25, China Wenchuan major earthquake has resulted in 62,664 people were killed and 358,816 injured, a total 23,775 were missing. Transfer of emergency rehousing 14385640, a total number of affected 4550.9241 million people.

• Rescue work is delayed because of disruption of transport and telecommunication. • Public services, such as water, electricity and gas supply, are cut off. • Land subsidence and landslides occur.

Further Damage A. More long-term effects • Aftershocks : Up to May 22, according to China Seismological Network Center determination, a total of Wenchuan area 4.0 times more than 169 aftershocks, the largest aftershock of 6.1. China Seismological Network Center experts said, five more aftershocks will continue intensive activities may be around two months.

Aftershocks

• Due to the dead bodies and contamination of water by sewage, diseases may easily spread out. • It is difficult to resume normal social and economic activities owing to the disruption of transport.

Landslide • Landslides are caused when the stability of a slope changes from a stable to an unstable condition. • It may cause landslide dam, which is a serious problem for the Chinese government to solve.

landslide dam ( debris dam ) • a natural damming of a river by some kind of mass wasting: landslide, debris flow, rock avalanche or volcano.Some landslide dams are known to be as high as the largest existing artificial dam .

• The water impounded by a landslide dam may create a dam lake . • Due to the earthquake-stricken area in Sichuan and rocks to plug a 35 dam lake . • last from short times to several thousand years.

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Consequences landslide dams frequently fail catastropically and lead to downstream flooding, often with high casualties. two types of flooding: backflooding (upstream flooding) upon creation and downstream flooding upon failure. Compared with catastrophic downflooding, relative slow backflooding typically presents little life hazard, but property damage can be substantial. Dammed groundwater surrounding groundwater level rises. The dam failure may trigger further catastrophic processes. As the water level rapidly drops, the uncompensated groundwater hydraulic pressure may initiate additional landslides. Those which fall into the dam lake may lead to further catastrophic spillages. Moreover, the resulting flood may undercut the sides of the river valley to further produce landslides downstream. After forming, the dam leads to aggradation of the valley upstream, and dam failure leads to aggradation downstream.