The powerful 6.3 magnitude shallow earthquake that hit New Zealand last week struck less than 6 miles from Christchurch’s historic downtown district, and only about 3 miles below the surface. Engineers were not surprised by the damage and tumbling of the older structures, since the epicenter of the quake was so close to the city, but the amount of damage to the more contemporary structures which had seismic retrofitting, was not anticipated.
With so many buildings in the United States using very similar, if not the same building standards as New Zealand, it is important for contractors to study the effects of this quake, before designing any new structures.
New Zealand Building Standards
New Zealand was as prepared as possible for earthquakes. According to Dr. René Tinawi, Manager of the Canadian Seismic Research Network, their construction code “is one of the most stringent in the world for new buildings.”
John Wilson, Chair of the Australian Earthquake Loading Standard, speaking on behalf of the Australian Science Media Centre noted that New Zealand, is a progressive first world country, and “has very good loading standards and a strict regulatory environment and since the mid-70s onwards, the building have been designed for earthquake resistance very well.”
Effect of the Earthquake
International engineers have just begun their investigations and it is too early to tell why these buildings failed. One reason for the structural failure could be that the buildings had been damaged and/or weakened by the prior 7.1 magnitude earthquake that occurred this past September. That earthquake, however, struck much farther from the city and did not cause nearly the amount of damage.
Nevertheless, there is already evidence that some of the buildings that had received seismic retrofitting failed. Amir S.J. Gilani, a structural engineer, said that Christchurch Cathedral, “which crumpled this week, had been retrofitted in the late 1980s and seemed to have performed well [during] last September[s earthquake].” Gilani continued to say that, “the retrofitting project had been used to showcase…advances in this field, however, it certainly experienced much larger accelerations in the 2011 earthquake for which it was obviously not prepared for.”
Since the time and location of an earthquake cannot be changed or predicted, builders need to be aware of prime areas where they are likely, and make sure to include seismic retrofitting in all plans.
Researchers, especially those in California, are worried that a situation like Christchurch could occur in the States. According to the LA Times, “California has about 7,800 such buildings in high-seismic zones, and many more vulnerable concrete-frame buildings.”
Architects are expecting tougher national building standards for strengthening old buildings to be enforced after seeing the damage from this earthquake. If tougher standards do come down, it will affect thousands of buildings that were built prior to 1970, when the current earthquake standards were released.