5.12 Wenchuan Earthquake - China's Natural Disasters

Wenchuan earthquake

The Wenchuan Earthquake was the most destructive and most extensive earthquake in China since 1949. The intensity and intensity of the earthquake exceeded that of the 1976 Tangshan earthquake. China Earthquake Research and Geological Disaster Research Experts Analyzed Wenchuan Earthquake Destructively Stronger Than Tangshan Earthquake

The main reason.

5.12 Wenchuan Earthquake

At 14:28:04 on May 12, 2008, Wenchuan and Beichuan in Sichuan Province struck a strong earthquake of magnitude 8. The earth trembled and the mountains and rivers shifted, causing devastating devastation. This is the most destructive and widespread earthquake since the founding of New China. The earthquake hit about 500,000 square kilometers of land in China! In order to express the deep condolences of the people of all ethnic groups across the country on the victims of the Sichuan Wenchuan earthquake, the State Council decided that the National Day of Condolences will be held from May 19 to May 21, 2008. Since May 2009, May 12th is the national disaster prevention and reduction day.

Loss of casualties

Local casualty summary (official)

According to the report of the Ministry of Civil Affairs, as of 12:00 on September 25, 2008, the Sichuan Wenchuan earthquake had confirmed 69,227 people were killed, 374,643 people were injured and 17,923 people were missing. According to the report of the Ministry of Health, as of 12:00 on September 22, a total of 96,544 hospitalizations for injuries due to earthquakes (excluding the number of patients in the disaster area) have been discharged 93,518 people, there are still 352 hospitalizations, of which the wounded in Sichuan Province is still hospitalized 153 People, a total of 4,273,551 people were treated and treated. According to the report of the General Staff, as of 12:00 on September 25, emergency rescue workers have rescued and transferred 1,486,407 people.

Regional deaths, injuries and disappearances
Wenchuan County 15941 34583 7930
Beichuan County 8605 9693 /
Bazhong 10 258 /
Nanchong 30 7632 /
Suining 27 402 /
Shifang 5891 31990 252
An County 1571 13476 /
Pingwu County 1546 32145 /
Pengzhou 952 5770 /
Mao County 3933 8183 336
Jiangyou 394 10016 44
County 103 1612 28
Yaan 28 1351 /
Leshan 8 534 /
Neijiang 7 225 /
Ganzi 9 23 /
Guangan 1 37 /
Zhangzhou 1 1 /
Liangshan 3 4 /
Zigong 2 87 /
Mianzhu 11098 36468 298
Dujiangyan City 3069 4388 /
Guangyuan 4819 28241 125
Qingchuan County 4695 15453 124
Chengdu 4276 26413 /
Meishan 10 315 /
Ziyang 20 633 /
Gansu 365 7865 11
Shaanxi 121 2932 /
Chongqing 16 637 /
Total 67551 281367 9148

Economic losses (as of September 4, 2008) The Wenchuan earthquake caused direct economic losses of 845.2 billion yuan. Sichuan is the most serious, accounting for 91.3% of total losses, Gansu accounting for 5.8% of total losses, and Shaanxi accounting for 2.9% of total losses. The National Bureau of Statistics classified the loss indicators into three categories. The first category was the issue of casualties, the second category was the issue of property damage, and the third category was the destruction of the natural environment. In the property loss, the loss of the house is very large, and the loss of private houses and urban residents' housing accounts for 27.4% of the total loss. Including schools, hospitals and other non-residential houses, the loss accounted for 20.4% of the total loss. In addition, there are infrastructure, roads, bridges and other urban infrastructure losses, accounting for 21.9% of the total losses, these three categories is a relatively large proportion of losses, more than 70% of the losses are caused by these three aspects.

Cause of earthquake

The Indian Ocean plate subducted into the Asia-European plate, causing the rapid uplift of the Tibetan Plateau to cause an earthquake. The plateau material flows slowly to the east, squeezing eastward along the Longmenshan tectonic belt on the eastern edge of the plateau, and meets the tenacious blockage of the rigid block below the Sichuan Basin, causing long-term accumulation of tectonic stress energy.

Eventually it was suddenly released in the Longmen Shan Beichuan-Yingxiu area. Thrust, dextrorotatory, extrusion-type fault earthquakes. The Sichuan earthquake occurred in the brittle-ductile transition zone of the crust. The focal depth is 10 km to 20 km. It is close to the earth's surface and has a long duration. It is therefore destructive and has a strong influence.

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Type of earthquake

The Wenchuan earthquake was a structural earthquake.

Earthquake Depth The Wenchuan Earthquake is a shallow source earthquake. (Earthquakes can be classified into shallow source earthquakes according to the depth of the source. Earthquakes occur within 60 km. The shallow source earthquakes are mostly distributed on the outer edge of the island arc, inside the deep trench, and on the mainland. The coastal part of the arc-shaped mountain range.The shallow source earthquakes mostly occur in the range of 30km or more below the surface of the earth's surface, while the deep-seismic earthquakes, the deepest ones can reach about 650km, and form an inclined seismic belt called Benioff. With the connection of shallow-source and deep-sourced earthquakes in the “blood”, it is a global structural theory called the “revolution of the earth science.” The shallow-source earthquakes are mostly distributed on the outer edge of the island arc. The inner part of the deep trench and the coastal part of the continental arc-like mountain range.) The depth of the focal depth is 10 km - 20 km, so it is very destructive.
Influence scope Unusual handshakes include the county within 50km of the epicenter and the large and medium-sized cities within 200km. Shaanxi, Gansu, Ningxia, Tianjin, Qinghai, Beijing, Shanxi, Shandong, Hebei, Henan, Anhui, Hubei, Hunan, Chongqing, Guizhou, Yunnan, Inner Mongolia, Guangxi, Guangdong, Hainan, Tibet, Jiangsu, Shanghai, Zhejiang, Liaoning, Many provinces (autonomous regions, municipalities directly under the Central Government) and Hong Kong, Macao Special Administrative Region of Taiwan as well as the Taiwan region of Fujian province have obvious sense of tremor. In addition to Heilongjiang, Jilin, and Xinjiang, China has different degrees of quake. Among them, the earthquakes in Sichuan, Shaanxi and Gansu provinces are the most serious. Even the Thai capital Bangkok, the Vietnamese capital Hanoi, the Philippines, Japan and other places have a sense of quake. Earthquake Intensity: The epicentral intensity of the Wenchuan earthquake was as high as 11 degrees. It was distributed in strips in the two centers of Yingxiu Town and Beichuan County in Wenchuan County of Sichuan Province, covering an area of ​​2,419 square kilometers. Among them, Yingxiu 11-degree district is located along the direction of Wenchuan - Dujiangyan - Pengzhou, and Beichuan 11th district is located along the Anxian - Beichuan - Pingwu direction. The 10-degree area of ​​Wenchuan Earthquake is about 3,144 square kilometers, showing a long stretch from north to east, and the northeastern end reaches Qingchuan County in Sichuan Province and Wenchuan County in the southwestern end. The area of ​​the 9-degree zone is about 7,738 square kilometers, and it is also spread in the northeast to the east and west. The northeastern end reaches the junction of Wudu District, Weinan City, Gansu Province and Ningqiang County, Shaanxi Province, and reaches Wenchuan County in the southwestern end. Solidified time
Destruction is extremely serious in areas above 9 degrees, and its distribution area is close to the seismogenic fault and follows the trend of the fault to grow into strips. Among them, the boundary between the 10 degree and 9 degree areas was affected by the shift of the Longmenshan Qianshan fault, and it protruded toward the basin in the mountains of Mianzhu city and Shifang city, and also highlighted slightly in the urban area of ​​Dujiangyan. The 8 degree area of ​​the Wenchuan earthquake covers an area of ​​27,787 square kilometers. The southwest end reaches Baoxing County and Lushan County in Sichuan Province, and the northeastern reaches the Xiayang County and Ningqiang County in Shaanxi Province; the 7 degree area covers an area of ​​84,449 km2 and the southwest end reaches Sichuan Province. In Tianquan County, the northeast reaches the Liangdang County of Gansu Province and Fengxian County of Shaanxi Province, the most eastern is Nanzheng County of Shaanxi Province, the west is Xiaojin County of Sichuan Province, the northernmost region is Maiji District of Tianshui City, Gansu Province, and the south is Sichuan Province. Ya'an Yucheng District. The 6 degree zone has an area of ​​about 314,906 square kilometers, and it extends to the west of Chongqing City and the north end of Zhaotong City in Yunnan Province. The southwestern end of the area is Jiulong County, Suining County and Heide County of Sichuan Province, and the northeastern end is the Zhenyuan County and Qingyang County of Gansu Province. The city, the most eastern part is Zhen'an County of Shaanxi Province, the west is Daofu County of Sichuan Province, the northernmost reaches Guyuan County of Ningxia Hui Autonomous Region, and the southernmost is Leibo County of Sichuan Province. In the transitional zone on the edge of the Longmenshan Basin, the intensity of the Wenchuan earthquake decayed quickly to the east, while the attenuation on the west side was relatively slow. At the same time, the intensity distribution of Wenchuan earthquake is also asymmetric in the north and south: the 8 degree zone and the 7 degree zone extend to the surrounding area, showing an irregular oval shape in the northeast, and the same intensity of the area is larger in the north than in the south and enter Gansu Province and In Shaanxi Province, the fault rupture was shown to propagate in the northeast direction, and the largest aftershock occurred in the north of the fault.

Expert Analysis

Feng Mei, an expert in the Institute of Geology and Mechanics of the Institute of Geomechanics at the Chinese Academy of Geological Sciences, who was visiting the portal of the Ministry of Land and Resources, pointed out that the Wenchuan earthquake was more destructive than the Tangshan earthquake.

First, it can be seen from the magnitude that the Wenchuan earthquake was slightly stronger. The Tangshan earthquake is internationally recognized as 7.6, and the Wenchuan earthquake is 8.0.

Secondly, from the perspective of the dislocation of the geopolitical mechanism, the Tangshan earthquake is tensile and falls off the wall. The Wenchuan Earthquake was built up on the wall and was more influential than the Tangshan earthquake.

Thirdly, the Tangshan earthquake fault dislocation time is 12.9 seconds. The Wenchuan earthquake is 22.2 seconds. The longer the dislocation time is, the longer the people feel the strong earthquake. This means that the duration of the Wenchuan earthquake is longer than Tangshan. The earthquake is stronger.

Fourth, from the index of the earthquake tensor, the Tangshan earthquake is 7.2, and the Wenchuan earthquake is 9.4, which is very different.

Fifth, the area affected by the Wenchuan earthquake was larger than the Tangshan earthquake. Feng Mei said that this is mainly due to the fault shifting. The Wenchuan earthquake is an extrusion fracture and the shifting direction is in the direction of the north east. That means the Wenchuan's northeast direction is affected more, but its western situation is better. some. The Mianyang Bell Tower Wenchuan earthquake affected a large area, and it is said that almost all of Southeast Asia and the entire East Asia region have felt. “The main reason is that the Wenchuan Earthquake has a long period of dislocation, which is longer than the Tangshan earthquake. This is why the Tangshan earthquake has a large number of deaths, but in fact the impact of the disaster is not as great as the Wenchuan earthquake.” Feng Mei said that because of the distribution of Wenchuan disasters wide.

Sixth, the geological disasters and secondary disasters induced by the Wenchuan earthquake are much larger than those of the Tangshan earthquake. Professor Jia Jiafa of the Ministry of Land and Resources Senior Consultation and Research Center said that because the Tangshan earthquake occurred mainly in the plains, the Wenchuan earthquake occurred mainly in mountainous areas, the types of secondary disasters and geological disasters are not the same, and the devastation caused by the Wenchuan earthquake is relatively large. Collapse, rolling rock and landslides are much more serious than the secondary geological disasters of the Tangshan earthquake. In addition, because there is more water in Sichuan, the barrier lake is also different from the Tangshan earthquake. An Meijian, an expert in the Institute of Geology and Mechanics of the Institute of Geomechanics at the Chinese Academy of Geological Sciences, added that the magnitude of the Wenchuan earthquake is slightly higher than that of the Tangshan earthquake and the energy difference is three times. The greater the energy of the earthquake, the more distant the earthquake is. Damage caused within the distance. In addition, the position of the Wenchuan earthquake is also very special. The Tangshan earthquake occurred in eastern China, because the delay line in the eastern region was relatively thin, and the seismic wave in the east was severely attenuated, while the delay line in Sichuan was thick, so the seismic wave attenuated slowly. From these two perspectives, the Wenchuan earthquake has a greater impact than Tangshan.