The province where the earthquake took place, Sichuan, is in western China and its capital is named Chengdu. It is surrounded by the Sichuan Basin. In the Great Sichuan earthquake, the epicenter was in Wenchuan County, Ngawa Tibetan and Qiang Autonomous Prefecture, which is 80 km north-west of Chengdu; and its depth was 19 km. On May 12, 2008, the earthquake occurred at 14:28 (China Standard Time) and the first tremor was felt. The earthquake was so strong that it was felt by cities like Beijing and Shanghai, and neighbour places like Hong Kong, Macau, Vietnam and Thailand also experienced tremors. The scope of the areas affected by the quake mainly included the north-east China along the Longmen Shan fault.
The Sichuan Basin was created 55 millions years ago, where the Indo-Australian Plate collided with the Eurasian Plate. These endogenetic forces create fold mountains, and therefore the Sichuan basin is bounded by mountains on all sides. As a consequence, areas around the Sichuan Basin are prone to earthquake. In 1933, there was a 7.5-magnitude earthquake occurring in north-west of Sichuan, causing 7500 deaths.
What has caused such a massive earthquake? To be precise, according to the United States Geological Survey, the earthquake occurred because of the motion on a northeast striking reverse fault on the northwestern edge of the Sichuan Basin. Since the crustal materials moved slowly from the high Tibetan Plateau, when they flowed to the strong crust underlying the Sichuan Basin and southeastern China, pressure gradually developed. The energy was then released in the form of seismic waves and thus led to the occurrence of the earthquake. Another possible cause is that the huge amount of water storage in reservoirs in Sichuan developed stress over the crust. The pressure stored may be released, causing an earthquake.
There were not any official warnings prior to the main quake. This is attributed to the fact that earthquakes are hard to forecast, and the results are not always accurate. However, it is said that there was a sign revealing the earthquake: a large number of toads were migrating in Sichuan two days before the main quake. These animals’ abnormal acts may reflect in earthquake events. In the Sichuan Earthquake, the China Earthquake Administration did not find strong evidence to show that an earthquake was to be occurred. Therefore, when the earthquake came, evacuation could not be made effective and thus a huge damage was resulted.
Then on 12 May, an earthquake indeed struck the area. The main quake of the Sichuan Earthquake took place at 14:28 local time, nevertheless, the rupture lasted for only 120 seconds. In the following three days, many aftershocks still threatened the people. There were 64 to 104 major aftershocks, with magnitude ranging from 4.0 to 6.1. These aftershocks continued to bring new deaths and casualties in the area. For example, on 17 May, an aftershock destabilized a slope and caused a landslide. On 25 and 27 May, the Qingchuan County had two aftershocks on the spot with magnitudes greater than 5. On 27 May again, an aftershock hit the Ningciang County.
Till 29 June, the number of deaths has reached about 70,000 and over 370,000 people were injured. More than 17,000 people were missing, and many people were made homeless. More than 15 million people must be evacuated out of the area, and about 45 million people were affected by the incident. As a recent natural hazard, the Sichuan Earthquake is definitely a severe one, with a tremendous destruction. This earthquake caused the most serious casualties and deaths after the occurrence of the Tangshan Earthquake in 1976.
Apart from the loss of lives, the earthquake brought about many impacts as...