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Aftershocks strike NZ

Engineers this week warned some areas of Christchurch, New Zealand might have to be abandoned after latest aftershocks from February’s earthquake.

Foundations compromised

Liquefaction damage caused by February’s devastating earthquake destabilised ground in the eastern part of the city so severely that foundations for buildings and bridges and roads were compromised (NCE 3 March).

Immediately afterwards New Zealand prime minister John Key said parts of eastern Christchurch may have to be permanently abandoned as a result.

Two major aftershocks struck the New Zealand city of Christchurch on Monday, causing major liquefaction and disruption existing clean-up efforts.

The first was a magnitude 5.5 quake and the second and bigger tremor, which struck just over an hour later at 2.20pm local time, was a magnitude 6.0 event, according to the US Geological Survey.

Remediation “could prove too costly”

Stafford said the ground shaking would have been quite severe for this to produce further liquefaction.

“When liquefaction occurs, the compaction usually produces denser sand [making it less likely to occur again],” said Stafford.

Imperial College London lecturer in modelling engineering risk Peter Stafford said that although no decision to abandon parts of the city this could happen if remediation work is considered too costly.

This week’s quakes and subsequent liquefaction have directly caused damage to roads and four key bridges, according the Christchurch Earthquake Recovery Authority (CERA).

The event has also left 30,000 households without power.

However, CERA said that power should be quickly restored and there is “no serious damage to the network”.
CERA is also considering whether to re-impose emergency conditions which were lifted in May depending on its assessment of infrastructure damage over the next couple of days.

Readers' comments (1)

  • More recent research may support Stafford's view but I seem to recall (from my PhD literature review) that work by Seed and others at Berkeley, California in the 1970s showed that once-liquefied materials were more easily reliquefied. I believe the thinking was that the initial liquefaction left the material in a looser (higher void ratio) state that before. Counter-intuitive, perhaps?

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