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The Sichuan earthquake of May 12, 2008, 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.
On a continental scale, the seismicity of central and eastern Asia is a result of northward convergence of the India plate against the Eurasia 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. The magnitude 7.5 earthquake of August 25, 1933, killed more than 9,300 people. - USGS Website
The eastern Xizang earthquake of October 6, 2008 occurred as a result of normal faulting in the Tibetan Plateau. The style of faulting is inferred from the characteristics of seismic waves radiated by the earthquake source. The faulting that caused the earthquake is a consequence of predominantly east-west oriented extensional stress that ultimately arises from the convergence of the India plate northwards with respect to the Eurasia plate at a rate of over 40 mm/yr. This convergence drives the uplift of the Himalaya Mountains and Tibetan Plateau and produces generally north-south compressional stresses on the north and south margins of the plateau. The plateau interior is spreading to the east and, as a result, is an area of east-west extension within the larger region of north-south compression. The epicentral region of the 2008 earthquake previously experienced a magnitude 6.1 normal faulting earthquake on July 30, 1992.
Download full detail PDF of Sichuan M7.9 from USGS (8.5M file)
BBC News Learning Guide on How Earthquakes Happen
USGS - Sichuan Earthquake Details
The Science Behind China's Sichuan Earthquake
Tectonics Observatory, Caltech
MIT Details on Sichuan Earthquake
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