By Tao Lai.
March 9, 2011. Earthquake Engineering Research Institute.
It has been two weeks since the Feb. 22, 2011 M6.3 Christchurch earthquake. Although this quake had a much smaller magnitude compared to the one last September, but because the rupture was much closer to the city, it shook Christchurch much more severely than the one six months ago.
The Central Business District (CBD) was particularly hit hard. Indeed both earthquakes caused the collapse here of many seismically vulnerable URM buildings built between 1885 and 1920s. Unlike the first quake, which hit the city at midnight when the CBD was empty, the second quake fiercely shook the city at 12.51pm when many people were working, shopping and having lunch. By March 7, 2011, 166 were confirmed dead and many are still missing.
Ground motions recorded at the city center indicate that the shaking intensity from last September’s quake was about 50-60% of current design strength, while the shaking by the smaller February event exceeds current design strength by about 50%.
The New Zealand government and the people of Christchurch responded to the catastrophe promptly and effectively. Within just two weeks, most streets have been cleaned and a significant number of unsafe buildings have been demolished to prevent secondary hazard. However, the extent of the damage, compounded by technical and financial challenges of restoration will mean that Christchurch has a difficult road ahead.
Authorities in New Zealand have estimated that one third of buildings in the CBD will need to be demolished, with another one third requiring repair or retrofit. The same sources have said that 10,000 houses will be demolished and another 100,000 repaired. The prime minister has indicated his concern for the financial health of New Zealand’s Earthquake Commission (EQC), and is considering an “Australian-style” disaster levy to help meet the Christchurch earthquake repair bill.
Within 24 hours of the event, AIR Worldwide estimated insured losses would be in the range of 5-11.5 billion NZD, which would exceed the losses caused by the previous earthquake. AIR’s estimate includes only building and contents damage. Since AIR issued its estimate, Swiss Re stated that insured losses may be up to 12 billion NZD. Christchurch officials estimate the reconstruction will cost 15 billion NZD and take about 5-10 years to complete. Some of the damaged areas are beyond repair and will likely have to be abandoned.
Due to the damage and sustained closure of the CBD, the employment of about 52,000 people (of a total population of Christchurch of about 360,000 people) remains uncertain. Media reported that hundreds of Canterbury University students have been transferred to Australia to continue study, some schools are likely to be closed for up to a year, and about one sixth to one fifth of the population has left, either temporarily or permanently.
Certainly, the earthquake has changed Christchurch. It is also likely to change the approach to managing natural catastrophes in the country. Both earthquakes occurred on a previously unknown fault, which suggests an a priori low probability of occurrence from an historical point of view. Unfortunately, low probability events do occur, and a once-lovely city is now struggling to recover.
Learning from Earthquakes: First person reports
