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Earthquakes give engineers a chance to reevaluate

Major earthquakes in Italy, Haiti and New Zealand in the past two years have shown the devastating effect they can have on infrastructure and communities.

The difference in death tolls between Haiti and New Zealand also highlights the need for buildings that can withstand the effects of a quake.

Engineers have a huge responsibility but how far can they go to protect communities? It seems much needs to be communicated in hazard perception.

“If you look at Haiti the hazard maps were wrong,”

Peter Sammond, UCL

“If you look at Haiti the hazard maps were wrong,” said University College London’s (UCL) professor of geophysics Peter Sammond. “They were understandable more concerned about Aids and hurricanes.”

No building codes

Haiti’s earthquake last year highlighted the dangers of inadequate building stock in seismic zones. The magnitude 7 earthquake struck about 25km from the capital Port-au-Prince at a depth of 8km.

Its effects were devastating – killing over 200,000 and injuring a further 300,000, and displacing over 2M people. Over 70% homes were destroyed or damaged.

A combination of virtually no building codes and poor appreciation of the risk – there was no similar quakes in anyone’s lifetime – contributed to the devastation.

Sammond is just beginning consultation on a £7M research programme called “Increasing resilience against natural hazards”.

He hopes the research will better combine social and hard sciences to help make people and infrastructure more resilient against earthquakes and enable the population to understand the risks.

Geologists charged

Risk perception was an important factor in the L’Aquila earthquake – a magnitude 6.2 that struck central Italy on 6 April 2009.

Several days before the some members of Italy’s Commissione Grande Rischi (Commission of Big Risks) reassured the local population that recent seismic activity did warrant any form of emergency action.

As a result many died or were injured when the quake struck in the middle of the night.

Victims’ relatives are taking legal action against seven members of the commission. Following last month’s Christchurch earthquake some academics have questioned why the authorities should have been taken by surprise.

The events in Christchurch will give engineers opportunities to learn.

“I don’t think they [New Zealand authorities] should have been surprised that the earthquake occurred in Christchurch,” said UCL reader in earthquake geology Gerald Roberts.

“They may have missed clues from the quake in September 2010 – it happens, sometimes you can’t see the wood for the trees.”

However, while experts cannot predict exact locations of quakes, they do know the areas where they will occur. Engineers can then use the latest techniques to help buildings withstand the resulting ground movements.

“It’s an aspiration to make buildings quake-proof but you have to pragmatic,” said Arup seismic specialist Ziggy Lubkowski.

“When designing to a code it’s important to recognise that things develop. In the case of the Christchurch earthquake we may learn more about the effects of vertical shockwaves.”

Lubkowski adds that there is always a trade off when designing buildings in seismic zones between cost and the ability to withstand a quake.

As in any project, designers will not want to over-engineer structures, which could potentially indebt owners with huge maintenance costs.

The events in Christchurch will give engineers opportunities to learn and implement any new effects that were previously not known.

Earthquake engineering field investigation team (EEFIT) is travelling to Christchurch next week to investigate how the structures responded in the quake.

Readers' comments (1)

  • Jonathan Gammon

    Checking on structural integrity can be an exercise fraught with difficulty. I remember being told about the inspection of a steel plate girder railway bridge. Train drivers had reported a loud bang every time they took their train over the bridge. Trains were prevented from crossing the bridge in order to allow a visual inspection to be carried out. No defects were found. However, an inspection engineer remained beside the bridge at track level when the trains began to cross at their usual speed. By luck, he was in such a position that he saw the briefest flash of light towards the top of the girder just before the bang occurred. Running a heavy train slowly over the bridge then showed that the connection between the upper flange and the web of the girder had failed and the girder had been significantly weakened. The opening of the joint under load resulted in the flash of light; the rapid closure of the joint on removal of the load resulted in the bang.
    Structural weakness as a result of an earthquake might also not be readily identifiable by visual inspection under static conditions if the structure returns to its original geometry. The weakness might only manifest itself in a subsequent earthquake event. At least for structures not retro-fitted to current Codes, perhaps it should be a requirement that instrumentation be fitted at critical connections so that any displacement that occurs during an earthquake can be recorded? This could then be taken into account when assessing the robustness of the structure to withstand a subsequent event.

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