Posted on 07 Sep 2010
New Zealand's South Island was rocked by a strong earthquake, causing ground motions and damage in Christchurch, New Zealand. Reported as a preliminary magnitude 7.4 event, the (revised) magnitude 7.0 event occurred at 4:35 AM local time on Saturday, September 4. The 12 kilometer deep earthquake occurred about 35 miles WNW of Christchurch and 200 miles south of Wellington, New Zealand.
AIR Worldwide estimates that industry insured losses to be between NZD $2,700 million ($2.0 billion USD) and NZD $6,000 million ($4.5 billion USD).
While design requirements for new construction in New Zealand are quite stringent, Christchurch -- the country's oldest city -- has many historical masonry buildings, which dominate the central business district. Few had undergone seismic retrofit and many were the target of strong ground motion caused by the earthquake, which is now estimated to have occurred at a depth of just 5 km and about 44 km from the city. The shallow focal depth will undoubtedly have exacerbated the damage.
Christchurch’s central business district was heavily affected. Streets lined with buildings of unreinforced masonry or frame with masonry infill walls are now littered with fallen bricks and broken glass. Whole sections of walls fell away from buildings' frames, and chimneys and parapets toppled. Officials in Christchurch have activated the Building Safety Evaluation process, roping off streets so buildings can be individually assessed. It is likely that many older masonry buildings—even those in which damage is not immediately apparent—will have sustained cracks that compromise structural integrity. Broken shop windows led to some looting and an overnight curfew was imposed, though it was said to be intended to protect people from falling debris. The state of emergency in the city is likely to remain in effect until at least noon on Monday. Meanwhile, inside shops, goods fallen from shelves litter floors. One fire broke out, which was thought to be caused by a surge when the gas and power supply was turned back on.
Significant damage to residential structures has also been reported, including some collapses in inland Canterbury nearer the epicenter. Much of the damage seems to have been the result of toppled chimneys smashing roofs and the contents beneath.
Many local roads were damaged and railways warped, though bridges seem to have escaped significant damage and regional highways are largely intact. Christchurch airport, which was closed for inspection following the quake, was reopened by early afternoon local time.
Injuries are numerous, but most are minor. Two people were seriously injured as a result of falling masonry and glass; one remains in critical condition. Remarkably, there have been no reports of fatalities, likely due to the fact that the earthquake occurred in the early morning before Christchurch’s commercial center became filled with people. The Red Cross has opened shelters for those whose homes are destroyed or unsafe.
Officials say that power has been restored to most homes and businesses in Christchurch. However, there is still no electricity in rural areas of Canterbury, where the quake toppled utility poles. In areas where broken mains cut off the water supply or where water has been contaminated, tankers will be used to bring in water. However, in the coastal town of Kaiapoi, north of Christchurch, officials are advising residents to leave town if possible, as it may take considerable time before clean water and sewage services are restored. In Christchurch, shelters have been set up to house those made homeless by the earthquake.
The earthquake is thought to have occurred on the Porters Pass-Amberley Fault Zone (PPAFZ), which forms the southern part of the collision zone along the Pacific-Australia plate boundary. Scientists at New Zealand’s Institute of Geological and Nuclear Sciences (GNS Science), however, are now speculating that it occurred on a previously unknown fault. GNS Science is joining forces with several local and regional universities to deploy 40 portable instruments in the epicentral region that will record aftershocks; data will be used to better understand the rupture mechanism of the main shock and to ascertain whether seismic stress may have been transferred to neighboring faults.