Rescue efforts continue in Christchurch to extract trapped people from destroyed buildings as fears grow that Christchurch’s highest hotel, the Grand Chancellor, may collapse as a result of damage sustained in the earthquake.
On psychological impacts:
The New Zealand Psychological Society has prepared the publication Life After Earthquakes which looks at methods of dealing with trauma in the wake of an earthquake. It can be downloaded here.
Professor John McClure, School of Psychology at Victoria University conducted a survey of people’s perceptions of risk before and after the September earthquake. He comments:
“As with all earthquakes, this earthquake shows the importance of preparation including strengthening buildings, not only having survival items such as an emergency kit. It shows that New Zealanders need to get over the idea that Wellington is the only place vulnerable to a major earthquake. As seismologists are well aware, they can happen in many parts of New Zealand.
“It is not enough to be aware of the risk, people also need to have an attitude that their actions can prevent harm and help them survive. Our recent study on perceptions of Christchurch citizens showed that Christchurch citizens who perceived the risk of an earthquake in the region as high before the September earthquake were no more prepared than those who perceived the risk as low.”
Potential impact on Canterbury business and tourism: University of Otago’s Caroline Orchiston last year completed a PhD thesis: Seismic risk and the tourism industry in the zone of the Alpine Fault, New Zealand: disaster preparedness and business resilience.
On building engineering standards:
From the AusSMC:
Prof John Wilson is Chair of the Australian Earthquake Loading Standard and Deputy Dean of Engineering at Swinburne University of Technology:
“This quake was pretty much a bullseye – it was quite a large Mn 6.3 event and so close to Christchurch that we weren’t surprised to see significant damage; at that close range, the level of shaking is quite severe. We expected the older buildings with unreinforced masonry to suffer – their masonry is heavy, brittle and vulnerable to earthquake shaking. In general the contemporary buildings performed well, although a few contemporary buildings have collapsed which did surprise us.
“New Zealand has very good loading standards and a strict regulatory environment and since the mid-70s onwards the buildings have been designed for earthquake resistance very well. What’s more, the standard of design has still been improving over the last 20 years or so – which is why most buildings performed well, with the exception of a few buildings that were severely damaged or partially collapsed. The immediate challenge is to allow the Urban Search and Rescue (USAR) teams to respond and rescue in what is a very hazardous environment with continuing aftershocks.
“It is definitely possible to make earthquake-proof buildings nowadays. The most elegant approach is to use ‘base isolation’ – basically you found the building on springs and de-couple it from the ground. It adds about five per cent to the building cost but makes it totally secure. The design has been around for about 30 years, though really became more common about 15 years ago. It’s widely used in California and Japan, which see so many earthquakes, but is also used in Wellington for buildings like their large museum.”
From the Canadian Science Media Centre:
Dr René Tinawi,Manager of the Canadian Seismic Research Networkand Professor Emeritus at the Ecole Polytechnique de Montreal (translated from French):
“The New Zealand construction code is one of the most stringent in the world for new buildings and it partially inspired our own Canadian Code. This is why Canadians experts would like to inspect first-hand how newer buildings fared during this second Christchurch earthquake, as soon as the situation allows.
“The Christchurch cathedral and many other masonry buildings without reinforcement have been severely damaged. It was already known that those were the most vulnerable buildings since their structure is only made of bricks, stones and concrete blocks.
“Even buildings that most effectively resist earthquakes and have an internal steel or reinforced concrete structure, may have a fragile external envelope (glass, bricks and stones) which can crash in the streets. Those falling bricks can be very dangerous even if the building itself is sound.
“Even relatively modern buildings can be vulnerable. Scientists now freely admit that building codes for earthquake prone regions from the sixties, were simply inadequate. Experts all around the world, in Japan, California, New Zealand, Canada, United States, all agreed that those standards were inadequate.
“New standards are now much better. First, because of all the new data scientists have collected from great earthquakes, in Chile, Alaska, California, Japan, New Zealand… And we now have large seismic laboratories and impressive computer tools and models which didn’t exist a few years ago.”
Dr Maurice Lamontagne, Research Scientist in Seismology, Geological Survey of Canada (translated from French):
“What surprises me the most is not seeing the damage to masonry buildings like the cathedral’s bell-tower but to see new concrete buildings crumbling down.
“It is true that New Zealand has excellent earthquake standards in its building codes, but those standards were much more stringent on the Alpine Fault to the west of Christchurch than in the city, where secondary faults are poorly known. Experts have been surprised that the town itself has been hit.
“As a specialist, I am surprised that this second earthquake is so far from the first one, more than 40 km, and so strong. Normally, aftershocks happen almost at the same place as the first quake, and they are much weaker.
“I think that this second earthquake with its own aftershocks, will provoke an intense anxiety in the population who thought they were safe after weathering a first large earthquake without much damage. Now, nobody knows what will happen.”
Dr Melissa Giovanni,Professor of Geology at University of Calgary comments:
What does a magnitude 6.3 earthquake mean?
“New Zealand is a first-world country, and the reason the damage is so much greater is that it’s an aftershock of the larger 7.1 magnitude earthquake that happened last September near Christchuch. The buildings were already weakened such that a magnitude 6.3 would be much more devastating – for example, cracked foundations and damaged support structures.
“Another reason this earthquake was more damaging is that it was closer to the surface, and so the movement would be more intense than in a deeper quake where the earth can dissipate some of the energy. The fault that broke, we call an oblique thrust, which means there was some horizontal movement and some vertical movement. So the initial movement probably felt like a lift as the earth moved vertically, and then later you would feel vertical and horizontal movement.”
Why did this earthquake happen here?
“In New Zealand, the North Island is located where two plates are converging – the Australian Plate and the Pacific Plate. On the South Island, the plates are sliding past each other in what we call a strike-slip fault, called the Alpine Fault. It’s similar to the San Andreas Fault in California.
“These plates are always in motion. As the plates are grinding and scraping past each other, it breaks rocks and causes earthquakes like what we’ve seen. The crust is still trying to regain its equilibrium since the 7.1 magnitude September earthquake near Christchurch. This most recent 6.3 magnitude earthquake is part of a series of aftershocks from the September event. Aftershocks have been common since September with several having magnitudes larger than 5.0. We can expect aftershocks to continue for days, weeks, and months.”
What properties of the location may have made this earthquake worse than it would have been elsewhere?
“It has to do with what the ground is like. Christchurch is located on the Canterbury Plain and is quite close to sea level. Groundwater levels are close to the surface, and much of the Canterbury Plain is underlain by loose sand with water in its pore spaces. The ground is usually stable, but as soon as it starts shaking, the water pushes the grains apart.
“Is there something special going on with plate movement to have caused these quakes?
“This is geologically common. Plate boundaries are in constant motion and the result of that motion is earthquakes. We’re not to the point where we can predict earthquakes, but we can certainly expect repeated events along any plate boundary around the world.”