The Sichuan 2008 Earthquake

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The Sichuan 2008 Earthquake Factors On 12 May 2008 at 14:28:01.42 CST, an earthquake, measuring up to 8.0 on the Richter scale struck the Wenchuan County of the southwest Sichuan province of China. The epicentre location was 31°01’16”N and 103°22’01”E. Between 64 and 104 major aftershocks, ranging in magnitude from 4.0 to 6.1, were recorded within 72 hours of the main quake. According to Chinese official counts, by October 23, there had been 34,498 total aftershocks. By September 2008, the recorded number of dead was 69,227, with 374,643 injured, 17,923 missing and at least 5 million homeless. The earthquake occurred under some of the steepest and most rugged mountains in the world, the Longmen Shan also called the Dragon's Gate Mountains. These mountains are on the eastern edge of the Tibetan Plateau and are steeper than the Himalayas. They are formed by the collision between the Indian and Asian tectonic plates that began about 55 million years ago. Two long faults in particular, running the length of the Longmen Shan, had slipped many millimetres during the last few hundred years. One of these faults resulted in the earthquake in Sichuan. Unlike the Himalayas, which have small earthquakes continuously, there is no historical record of earthquakes above magnitude 6 in the Longmen Shan region. Therefore, while scientists knew the faults were there and active in the Dragon’s Gate, no-one ever expected an earthquake of this size. The Geomorphological evidence suggests that the faults are very steep with mainly lateral or strike-slip displacements taking place over time. Global Positioning Systems measurements show a greater proportion of thrust or shortening displacement than lateral displacement faults. The observations of seismologists suggest both things: more thrust in the SW, nearer the epicentre, and more strike-slip toward its
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