The 2008 Great Sichuan / Wenchuan Earthquake
The 2008 Sichuan Earthquake was one of the most disastrous earthquakes in terms of destruction, cost, casualties and other factors. It is five years today (May 12th 2013) since this earthquake struck China on the 12th of May 2008 at 02:28:01 pm local time.
The quake struck with a magnitude of 7.9 on the Richter scale and lasted for about 2 minutes, destroying millions of homes and buildings including schools and hospitals, damaging dams, breaking water pipes and gas mains, causing power failures, disrupting telecommunications, creating dangerous quake lakes, destroying and damaging roads and railways, killing and injuring thousands of people, leaving millions homeless, leaving many children orphaned and many more.
The epicentre of the quake was in the Wenchuan county in the Sichuan province and hence it is also mentioned as the Wenchuan earthquake.
Longmenshan fault system:
This earthquake occurred along the Longmenshan fault and hence we will briefly look at the details about this fault.
The Longmenshan fault zone or fault system is made up of a few faults; in other words, there are a few faults that lie within the Longmenshan fault zone. This fault is found at the base of the Longmen mountains in the Sichuan province of China. The cause of the fault is the continental convergence of the Indo-Australian plate and the Eurasian plate. The earthquake occurred due to a rupture on this fault which in turn ruptured two other faults in the fault zone. The rupture was due to the motion of the tectonic plates.
The Longmenshan fault is a thrust fault, where ground on one side of the fault moved up or over the ground on the other side. Thrust fault is a reverse fault at a very low angle. If you look at the pictures to the right hand side, you will get a better understanding of the different types of faults and also the difference between a reverse fault and thrust fault.
Details of the 2008 Sichuan earthquake:
- The epicentre of the earthquake was in the Wenchuan County, Sichuan which is a mountainous region in western china. The depth of focus of the quake was 19 km. The quake occurred on the 12th of May 2008 at 14:28 hours local time and lasted for about two minutes.
- The magnitude of the quake was 7.9 with intensity XI on the intensity scale.
- The quake was felt in the neighbouring countries of Beijing and Shanghai (more than 1,500 km away from epicentre) where buildings swung due to the tremors.
- The fault broke to a length of 240 km
- There were thousands of aftershocks even after months of the quake and killed more people and caused more damages.
Cause of the 2008 Sichuan earthquake:
- The earthquake occurred on the Longmenshan fault system that lies along the border of the Indo-Australian plate and the Eurasian plate in the eastern border of the Tibetan plateau. The quake occurred due to the rupture on this fault, which occurred starting from Wenchuan. The quake waves travelled north-east at an average speed of around 3.1 km per second.
- The rupture was due to the impact of Indian plate striking on the Eurasian plate (reverse fault) pushing it northward. The total length of the rupture was 240 km and the maximum displacement was around 9 metres.
- This fault system has many other faults in which two of them were ruptured; the Yingxiu-Beichuan Fault (YBF) and the Guanxian-Anxian fault (GAF).
Reason for high intensity earthquake and heavy damage:
- The earthquake occurred in a region of the fault that was along the place where the mountain and basin met. The Sichuan basin area is made up of soft sedimentary rocks, so when seismic waves travel through this area, they slow down and increase in amplitude.
Note: Seismic waves travel faster in rigid terrain (this is the reason why the effect was felt in far away cities) and they travel slower in sedimentary plains (reason for more destruction in the Sichuan basin area).
General rule, soft rocks shake more (easier to shake) compared to rigid rocks, hence the higher intensity of the quake and severe damage in Sichuan area. More than 100 million people live in this area.
- Also the depth of focus or focal depth (the depth of the quake) of the quake was shallow.
- Again in the mountain region, earthquake caused hill slides and landslides and hence buried the towns in this area. This hindered relief work and also blocked rivers to form lakes which later broke due to accumulation of more water, leading to more destruction.
Note: Focal depth and epicentre are two different terms in an earthquake. The pictures to the right hand side will clearly help you distinguish between these two terms
Focal depth - is the point within the earth where the rupture initiates.
Epicentre - Point vertically above the focal depth of the earthquake on the surface of the earth
Different views about why this earthquake occurred:
- According to USGS, the displacement was around nine metres along the length of the fault and there were surface deformations greater than three metres.
- According to the Japanese seismologist Yuji Yagi from the University of Tsukuba, the earthquake took place in 2 stages.
In the first part, the Longmenshan fault was ripped apart by seven meters.
In the second part, the fault sheared by four meters. The total quake lasted around two minutes. The severity of the earthquake was due to shallow focal depth of the quake.
- According to Japanese seismologist Teruyuki Kato from the University of Tokyo, the seismic waves travelled long distances without losing their energy, because of the firm terrain in Central China.
- It is also believed that this earthquake was triggered by the construction and the filling of the Zipingpu dam (50 stories tall situated 5.5 km from epicentre of earthquake) that released the tension between the two sides of the fault causing them to move apart. However this was not the cause, the dam could have just triggered the earthquake earlier than it was supposed to happen.
Damages and casualties in the 2008 Sichuan earthquake:
- This quake is considered to be one of the 21st deadliest quakes of all times with 69,195 casualties, 18,392 missing and 374,643 injured.
- Around 4.8 million people were left homeless but estimates predict that it could be as high as 11 million as the government did not release the official figures. The population in the affected area was 15 million.
- There were 149 to 284 major aftershocks and more than 42,719 aftershocks in total that occurred through to the 28th of May 2008.
- More than eighty percent of the buildings were destroyed and most of this was due to the poor construction.
- Almost all provinces in China except Xinjiang, Jilin and Heilongjiang were affected by the quake.
- Two chemical plants collapsed in Shifang leading to leakage of Ammonia and sulphuric acid in large quantity and hundreds of people being buried under the debris.
- A school in Dujjangyan collapsed with hundreds of students buried under the debris.
The Wenchuan China Earthquake May 12, 2008
- Juyuan middle school collapsed and many students were buried.
- The security guards at a Panda reserve were killed in the quake. One Panda died being smashed by the walls in her enclosure. The other pandas in two reserves close to the epicentre survived but many with injuries. Not much is known about the pandas in the wild.
- The Zipingpu Hydropower plant had minor damages and is structurally safe and stable.
- The Tulong reservoir is in danger of collapsing.
- Around 391 to 400 dams were damaged due to the quake.
- Thousands of school children died due to poor construction of school buildings. (19,065 students died and 546 disabled). Around 4,727 children were orphaned.
- Around 7,000 school buildings collapsed throughout the provinces and a total of 21 million buildings were damaged.
- An estimated 5 million people were left homeless, millions of livestock were killed and agricultural lands were damaged.
- Around a million pigs died in the Sichuan province
- The total loss due to the quake is estimated to be $123 billion as property loss and $147 billion (1 trillion yuan) as economic loss.
Other countries that felt the effect of this quake:
Hongkong and Macau felt tremors three minutes after the quake and that lasted for 30 seconds with intensity III, the shaking was felt in Vietnam, Thailand felt shaking from the tremors six minutes after the quake, with buildings swinging for few minutes, Taiwan and Mongolia felt tremors almost eight minutes after the quake, Nepal and Bangladesh felt tremors, India felt tremors almost nine minutes after the quake, and tremors were also felt in Russia and Pakistan.
- There were around a hundred major aftershocks within seventy two hours of the major quake and these had magnitude between M4.0 and M6.1.
- According to data on the 6th of November 2008, there had been more than 42,700 aftershocks in total, out of which 246 had intensities between 4.0 and 4.9, thirty four of them had intensities between 5.0 and 5.9 and eight of them had intensities between 6.0 to 6.4.
- An aftershock on May 25th measuring M6.0 occurred in Qingchuan county, Sichuan and caused deaths and injuries to around a thousand people and destructed thousands of buildings.
- Two aftershocks on the 27th of May (M5.2 in Qingchuan county, M5.7 in Ninggiang county) injured 63 people and more than 420,000 homes collapsed. There were two more aftershocks in the same area on the 23 of July 2008, killing one, six injuries and damaging hundreds of homes and highways
- There was an aftershock of M6.1 on the 1st of August 2008 in the Pingwu and Beichuan counties causing two deaths, 345 injuries, collapsing and damaging hundreds of houses and damaging highways.
- An aftershock measuring M6.1 occurred on the 5th of August 2008 in Qingchuan, killing one and injuring thirty two people. It caused hill slides and disrupted telecommunications.
A complete list of all the aftershocks with details of time, date, location and magnitude can be found on the link below:
Aftermath of the 2008 Sichuan earthquake:
- Many main buildings in Shanghai, for example, the Jin Mao Tower and Hongkong New World Tower were evacuated.
- Workers in industries were evacuated
- The international airport at Chengdu was shut down and was opened later in the evening with restricted service.
- Most of the office towers in Beijing were evacuated.
- There were cracks in many buildings in Chengdu
- A cargo train that was carrying tanks of petrol derailed due to deformation caused in the railway tracks and caught fire. Many other railway systems were buried.
- Rescue troops were delayed due to all the highways to Wenchuan being damaged.
Landslides Threaten Sichuan Province
- Trade was suspended in the Shanghai and Shenzhen stock exchanges.
- All mobile, landline telecommunications and internet were disconnected for the affected and surrounding areas.
- Many relief workers were killed due to landslides when they were repairing roads.
- Some Taiwanese tourists were trapped inside cable cars on the Lingyanshan Ropeway.
- Due to the high magnitude quake and the many aftershocks, a large number of rivers were blocked by landslides. These formed lakes called “quake lakes” and around 34 such lakes were formed out of which 28 were in danger to local people, according to reports on the 27th May 2008.
- Worst of the quake lake was the Tangjiashan quake lake which was in a location inaccessible by road or rail transport and was the largest of all the quake lakes. 17 helicopters were involved in this operation of breaking the lake, where engineers, explosive specialists, earth moving tractors, tons of fuel for the machineries were airlifted. 1,200 soldiers arrived by foot and 200,000 people living downstream in Mianvangbyon were evacuated on the 1st of June 2008 in anticipation of the dam bursting.
- In June 2008 a quake lake that was formed as a result of landslide broke open, flooding one of the devastated towns in the low lying areas. This dislodged damaged buildings, cars and corpses.
- People mourned for earthquake victims on 19th May 2008 at Tiananmen square, Beijing.
- National mourning was declared by the state government for three days from 19th May 2008.
- National and regional flags flew at half mast.
- On the 19th of May 2008, a week after the quake, at 2:28 pm local time, people stood in silence for three minutes.
- The relay of the Beijing Olympic torch was suspended during the mourning period
- Many Chinese websites had their home page in black and white and television channels had their logos in grey and displayed banners about earthquake and relief efforts.
- Casinos were shut down and online gaming servers were shutdown.
China Blows Up 'Quake Lakes'
- The Chinese Government spent hundreds of billion dollars on relief and reconstruction.
- A few emergency medical teams were sent to Wenchuan county by the ministry of health.
- Thousands of troops from Chengdu Military region and armed police were sent to the Wenchuan county to help with relief work.
- Level II emergency contingency plan was started by the National Disaster Relief commission.
- An emergency relief team of around two hundred people was sent to Wenchaun County. The team consisted of Seismologists, commanders from military and army doctors.
- Due to worse land conditions, rescue operations were difficult. Helicopter evacuations had to be used and hundreds of Tibetan villagers suffered without food and water in their villages for around 5 days.
- Rain and landslide also affected rescue efforts badly
- Over 150 aircraft were involved in relief operations which included army, airforce and civil aircraft
- China accepted international aid to cope with the quake.
- Tzu Chi foundation and Red cross society from Taiwan sent around hundred tonnes of relief supplies
- Rescue teams from neighbouring countries joined the rescue efforts on the 16th of May 2008.
- U.S sent tents and generators through its air force
- 135,000 Chinese troops and medical officers were involved in rescue efforts across all the cities and counties.
- Jet Li’s "One foundation" also helped with rescue efforts.
- Programs were hosted where political figures, entertainers, businessmen etc., participated to raise money for relief work.
- Hong Kong actor Jackie Chan donated $1.57 million to the victims on the 24th of May 2008 and also said that he wished to produce a movie about this disaster.
There is a controversy that natural disaster prediction expert and geologist Geng Qingguo had predicted this earthquake and that it was dismissed by other mainstream seismologists.
Geng Qingguo also claimed that he sent a confidential letter to the State council office and also a report to the State seismological Bureau with information about the upcoming quake.
A few pictures from the 2008 Sichuan EarthquakeClick thumbnail to view full-size
Facts about the 2008 Sichuan Earthquake:
- This was the deadliest quake since the 1976 Tangshan Earthquake (around 240,000 people were killed) and the strongest quake since the 1950 Chayu earthquake (magnitude 8.5) in China
- The USGS warned about risks of major aftershocks over the next few weeks and months with some above M7.0
- The highest aftershock measured was M6.4 and an aftershock greater than M6.0 occurred on the 5th of August 2008.
- The Central government of China as part of the Chinese economic stimulus program officially informed that an amount of around $146.5 billion (1 trillion yuan) would be set aside to rebuild the areas affected by the quake.
- The area where the quake hit, was a rural area with poor healthcare, where poor people lived and was neglected by China’s economic rise.
- Buildings were not designed to withstand earthquakes and hence the reason for high percentage of damage in buildings.
- According to data released by the Chinese government on the 21st of November 2008, 200,000 homes were rebuilt and 685,000 were under construction. 1.94 million families still remained without permanent shelter. 1,300 schools were reconstructed. 25 counties were relocated.
- Internet was used as a source for rescue and recovery efforts during the rescue times. For example, to check contact information of victims, evacuees, landing spot for helicopters etc.
- On children’s day, which is the 1st of June 2008 in China, many parents who lost their children went to the school rubble and mourned.
- The ruins of the Beichuan county seat that was sealed officially was opened to public on the first anniversary of the quake, and this will remain as a reminder of the disastrous earthquake.
- The government dismissed warnings of so many dam projects in seismic zones and hence has denied access to seismological and geological data to researchers for investigating on causes of the quake
- There were protests from parents regarding poor school buildings that collapsed and killed thousands of children. The protesters were harassed by the police and made fun of by the government. They were paid little money (USD 8,800) as compensation and per-parent pension (USD 5,600) in order to maintain silence.
- A rescue helicopter that carried earthquake survivors and crew members crashed due to fog and turbulence on the 31st of May 2008.
- Government of China provided free aid for reversing sterilizations to parents who lost their only child in the quake.
Thank you for reading. Please leave your feedback and comments and also do not hesitate to share your thoughts or experiences if you have any.
The figures regarding damages, casualties and other information have been collected after research and data from various sources. Please feel free to comment if there are any errors so that this hub can be updated.
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