Ground liquefaction a factor in New Zealand earthquake

Guardian : The damage caused by Tuesday’s earthquake in Christchurch, New Zealand, caught many experts by surprise. The severity of the damage appears to be due to a combination of the earthquake coming from a previously unknown fault that runs beneath the city, building weakening caused by the 2010 earthquake, and the violence of the shaking because the city rests on damp sediments. “Liquefaction is a huge problem in Christchurch because the city is built on an alluvial plain, on sediments that are vulnerable to liquefaction,” said John Clague, an expert in natural hazards at Simon Fraser University in British Columbia. “When shaken, these sediments transform into a liquid, causing irregular settlement of the ground, which is extremely damaging to buildings and buried structures, like water lines.”