The Canterbury earthquake on Sept 4th was unusual because no one was killed. It is the only city in the world which has experienced a 7.1 magnitude earthquake without any deaths.
Part of the reason for this is our building code. New buildings have to be strong enough to withstand a big earthquake. The Civil Defence Headquarters during this emergency is the new Art Gallery, which has large panes of glass right along one side. It survived the earthquake with no damage at all.
Many old, historic buildings have been earthquake strengthened in the last 20 years. Most of these buildings had no damage or only a little. Unfortunately, the Arts Centre, which was built from 1877 onwards, suffered some damage. It was the site of the University of Canterbury until the University moved out to Ilam in the 1970s and 80s. These buildings had been earthquake-strengthened and that saved the buildings. They can be repaired but at a cost.
We are hearing the word “liquefaction” a lot now. Many areas in Christchurch, near rivers or the sea, are on sandy soil. During the earthquake, the water underneath the soil squeezed through the sand and mud, making cracks in the ground and pushing mud on top of grass and concrete. In some places the soil bubbled like little volcanoes. This is liquefaction. Even new houses developed cracks in the floor, walls and ceilings. There are maybe 4,000 homes badly damaged this way. One new subdivision near the sea, used machines to compact the soil – to push it down until it was firm. No houses were damaged in that area.
Engineers around New Zealand and from overseas want to find out how to build houses and bigger buildings so that they survive earthquakes. Christchurch might give them some answers.
Questions
1. Are there other areas in New Zealand which could suffer liquefaction?
2. Would buildings in your home town survive a big earthquake?
3. Earthquake strengthening is very expensive. If you are the owner of an old office building, would you pay for earthquake strengthening?
4. Are there other reasons why there were no deaths as a result of this earthquake?