The geography of science - Sichuan Earthquake (2008): lessons learnt?
Key question and ideas
- How do earthquakes happen?
- What can be done to reduce the impact of earthquakes on people and places?
- Earthquakes affect a huge number of people
- Physical processes
- Human processes
How do earthquakes happen?
The earth's crust is made up of huge tectonic plates which move slowly on the molten mantle beneath the earth's crust. The plates meet on conservative (plates slide past each other), destructive (plates collide into each other) and constructive (plates move away from each other) plate boundaries. Earthquakes occur along these plate boundaries or fault lines.
The impact of the 2008 Sichuan earthquake
The Sichuan earthquake occurred along a destructive plate margin, where the Indo-Australian Plate and the Eurasian Plate collide. The earthquake occurred along a mid-fracture (known as the Yingxiu-Beichuan fracture). The earthquake in Sichuan was a magnitude 7.9 on the Richter Scale, occurred at a depth of 19 meters and its epicentre was in Wenchuan, north-east in the Sichuan Province.
Dams - it is estimated that approximately 400 dams have been affected by the Sichuan earthquake (2008). The safety of these dams is a concern as many may not have been designed to withstand earthquakes. Some Chinese and US scientists believe that the quake could have been triggered by the huge Zipingpu dam. The dam is 50 stories tall and holds back several hundred million tons of water in the Zipingpu reservoir. It is situated just 500 meters from the Beichuan fault, only 5.5 kilometres from the epicentre of the earthquake. The Beichuan fault would have been under natural stress but this would have been multiplied by 25 times due to the weight of the water in the reservoir.
The Sichuan earthquake killed approximately 70,000 people, although other estimates put the total far higher. More than 10,000 children were killed when their schools collapsed or were buried beneath landslides. At least 4,727 children were orphaned as a result of the quake. The quake also left five million people homeless and 375,000 people injured. The impacts of this quake will be felt for generations to come especially as families tend to have only one child due to China's strict ‘One Child Policy'. Other impacts of the quake include: the collapse of buildings, particularly in the Beichuan County, the collapse of two chemical plants which led to the leakage of 80 tons of liquid ammonia which buried many people. Schools, homes and buildings were destroyed.
Reducing the impact of Earthquakes on people and places
The Sichuan earthquake killed many people due to unsafe building construction, particularly that of schools which were referred to by local people as ‘tofu dregs'. There is a great deal in modern construction techniques which can be done to reduce the impact of earthquakes on people and reduce the death toll. Within the USA, there are strict building codes for buildings within earthquake zones. These can help ensure minimum standards of building. In addition, instruments are installed in public buildings to measure the response of buildings to earthquakes. The response of buildings to earthquakes can be measured and then alterations to their construction can be made. It is also considered that metal buildings are far better at withstanding an earthquake than concrete ones because metal ones are more ductile (they can bend and flex without breaking). It is also important to consider the distribution of weight. A building which is top heavy is much more likely to fall than a building which is light weight on the top. Therefore, an earthquake building should be constructed of steel rebar but should be framed with lighter materials in the upper floors and have a heavily reinforced lower section. However, just because it is made of metal, does not mean it will not fall down during an earthquake.
In the USA, residential buildings are designed so that the roof falls directly in the middle of the room but stays up near the wall. People are then advised to take shelter in the doorways and away from the middle of the room. Scientists have considered the side to side movements during an earthquake in the design of earthquake proof buildings. However, they are now considering the up and down (vertical) movements also. To ensure that buildings are able to move in all directions, scientists suggest isolating the building from the ground in order to reduce the vibrations from an earthquake. Instead of having the foundation rest directly on soil or rock, use a material that will provide a cushioning effect and reduce the energy transfer from the ground to the building. Also, using liquid dampers. These are like putting a water tank at the top of the building. These are particularly useful where there are high winds.
How do earthquakes happen?
Use the BBC's interactive earthquakes resource (online or print out) to explore how earthquakes happen. Note down key words from this resource and write a short paragraph summarising how earthquakes happen.
Comparing two earthquakes in China: Tangshan (1976) and Sichuan (2008)
Watch and read the PowerPoint China Earthquakes: Learning from the past and read the Sichuan quake factfile, referring particularly to the section "Poorly constructed schools".
Complete the card sort activity entitled Learning from the past: Tangshan and Sichuan compared. By doing this you start to think about how the two earthquake case studies are similar/different to each other.
Then produce a Venn-diagram on a large piece of paper to compare the two earthquakes. How were the earthquakes similar? How were they different? Once you have completed your diagram discuss and share your ideas with the class.
For the second part of this activity use the resource sheet Learning from the past: Changing the future. Write an email response to the Chinese Government with recommendations of how they could prepare better for another earthquake. Use this ScienceDaily link and search ‘Earthquake resistant building' in Google images to help.
Feed back your recommendations on how the Chinese government could reduce the impact of earthquakes in China to the class.
Design your own earthquake resistant building. Here are some key points to think about in planning its construction: How will you stop the building from falling down? If the building does not fall down, how will you prevent accidents both inside and outside as it moves? What about falling glass and rubble on the people outside?