Department of Civil and Environmental Engineering
All about earthquakes
The world’s sixth largest earthquake in 2003 struck the remote Fiordland area of New Zealand. Details of this earthquake are available on the US Geological Survey (USGS) website.
Civil Engineers design buildings, bridges, dams and embankments to withstand earthquakes. New Zealand is a seismically active country so engineers in universities and research labs have done research that has been at the forefront of international work on improving earthquake performance.
Earthquakes occur when deep movement causes rocks to break deep underground usually 5-200km down. This generates a shock that propagates as a series of waves. Different types of waves travel at different speeds. When the waves arrive and how strongly they are felt depend on how deep the hypocentre is. Different types of rock and soil influence this too.
One type of seismic wave is a pressure wave (P-wave )and another is the S-wave. The animations show how they travel around the world, the difference in arrival time of the waves and how this allows the location of the earthquake to be identified.
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This animation demonstrates how strongly the different types of waves are felt.
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This animation demonstrates how different types of waves travel at different speeds.
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This animation demonstrates the difference in arrival time relative to the hypocentre.
To resist earthquakes, buildings can be built very stiff and very strong but this gets very expensive when they are large. It saves a lot of money if they can be made to flex in a major earthquake and sustain some damage but stay standing and save lives. One way is to make the vertical columns stronger than the beams and design the beams to crack but stay together so people are safe and able to leave the building after an earthquake.
New Zealand engineers led the world in another way of dealing with earthquakes. This is to put the building on a flexible base so the building moves gently while the ground shakes violently underneath it. This is called base isolation.
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This animation demonstrates how a building would behave with stronger columns in an earthquake.
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This animation demonstrates how a building would behave with the use of a flexible base.
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