Tuesday, April 27, 2010

Tectonic Summary of Magnitude 6.9 - SOUTHERN QINGHAI, CHINA Earthquake, 2010 /04/13

 The southern Qinghai Province, China earthquake of April 13, 2010 killed at least 2183, missed 84, injured 12,135 and many building were damaged Yushu County. It occurred as a result of strike-slip faulting in the tectonically complex region of the eastern Tibetan Plateau. This earthquake occurred several hundred kilometers north of the convergent India:Eurasia plate boundary, where the Indian Plate is moving northwards with respect to Eurasia at a rate of approximately 46 mm/yr. This convergence drives the uplift of the Himalaya Mountains, at a rate of approximately 10 mm/yr, and the Tibetan Plateau, which is an extremely broad region of thickened and uplifted crust sitting above 4.5-5 km. 

Fig: Map of CHINA 

In the region of the April 13 earthquake the Tibetan Plateau is extending and translating east-southeastward within a larger zone of generally north-south convergence. Based on the location, depth, and moment tensor of the event, the Qinghai Province earthquake likely reflects the interplay amongst these major tectonic forces, dominated in this location by southeastward translation along the Yushu fault, a strand of the larger Xianshuihe fault system. This fault accommodates approximately 9-12 mm/yr of motion, approximately one third of the overall eastward motion of Tibet. The April 13 earthquake is one of the largest known historic earthquakes within several hundred kilometers of its location. In 1738, a nearby earthquake of approximately magnitude 6.5 caused over 300 fatalities. Historic ruptures on the Xianshuihe fault system further to the southeast include the 1792 magnitude 6.8 earthquake; the 1816 magnitude 7.5 earthquake; the 1904 magnitude 7.0 earthquake; the 1973 magnitude 7.6 earthquake; and the 1981 magnitude 6.9 earthquake (Allen et al., 1991). 

 N.B. Major Tectonic Boundaries: Subduction Zones -purple, Ridges -red and Transform Faults -green in fig.
The magnitude 7.9 Wenchuan (Sichuan) earthquake of May 12, 2008 occurred on the margin of the Tibetan Plateau, in contrast with the April 13, 2010 earthquake, which occurred in the plateau's interior. The 2008 earthquake killed over 70,000 people and displaced over 15 million.