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Assumptions must be reassessed

Paul Jowitt

Christchurch quake was a huge surprise.

When earthquakes occur in well-known seismic zones, they don’t usually come as a surprise. However until recently it was not known that the quiet garden city of Christchurch lay on a major faultline, even though New Zealand itself is prone to earthquakes.

The country has some of the most advanced seismic codes in the world, thanks to the work of Bob Park, Tom Paulay and others at the University of Canterbury in Christchurch, and this has prevented more widespread devastation like that witnessed in such as Haiti, Chile and Pakistan.

I have spent considerable time in Christchurch, most recently as ICE President giving the IPENZ/University of Canterbury Hopkins Lecture.

Ironically, I also helped launch the Park-Paulay Fund to support further study and research in structural and earthquake engineering.

The effects of the September event were relatively benign - no deaths and no widespread damage, although the many aftershocks caused some distress within the city’s population.

But it seemed that that was that. Not so.

Last week’s quake was much closer to the city centre, and only 4km deep. It has resulted in more than 200 dead and destroying a third of the Central Business District and many other properties in the Christchurch area.

Liquefaction of loose sediments has been a major source of structural and foundation failures. Vertical accelerations (up to 2.2g) were far higher than those reasonably assumed when the codes were drawn up in the 1970s, and when the focus was on lateral ground motions. But in any event, it seems that the code’s return period of 500 years has been exceeded by a factor of at least two or three times.

In due course, the key assumptions in the codes will be re-examined by our engineering colleagues in New Zealand and worldwide.

The aftermath of such an event really highlights the critical role of engineers in the recovery, as local engineers continue to inspect buildings at great personal risk. Salute them. They are the unsung heroes.

It also brings into sharp focus the issues of resilience and the interactive effects of infrastructure networks; a key theme of my presidential address. The damage isn’t just to buildings - it goes beyond that, disrupting sewerage, water supply, power and communications networks, bringing civilised society to a standstill.

Reinstating basic infrastructure will be a major challenge. But through the support and dedication of the local engineering community and the strength of the Kiwi spirit, the recovery will happen. And the Land of the Long White Cloud - “Aotearoa” - will re-emerge from the long grey cloud that covers it in the wake of this devastating event.

  • Paul Jowitt is a past ICE President

Readers' comments (1)

  • Thank you Paul for your support. From the other side of the world in this one article you have given more encouragement than certain organisations have here. I am prouud to be an ICE member.

    Graham Boorman

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