10 years since the Darfield earthquake rocked New Zealand: what have we learned?
- Written by Mark Quigley, Associate Professor of Earthquake Science, University of Melbourne
Many of us may remember the magnitude 6.2 earthquake that hit Christchurch, New Zealand, on February 22 2011. The quake caused 185 deaths, thousands of injuries and billions of dollars in damage and economic loss.
But six months before that earthquake an interconnected maze of previously unidentified active faults ruptured beneath the alluvial plains some 20km to 80km west of Christchurch.
This multi-fault rupture produced a magnitude 7.1 earthquake that released 13 times more energy than the Christchurch earthquake. It was named the Darfield earthquake, after the nearest town, and violently shook us from our beds at 4.35am on September 4 2010.
No deaths occurred, but the significant damage to land and infrastructure stimulated numerous scientific investigations.
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Ten years on and it is useful to summarise some of the lessons learned in its aftermath.
Early discoveries
Within hours of the Darfield earthquake, scientists rushed to the scene. They located evidence for a major ground surface rupture at Highfield Road (pictured above).
This site quickly became a geological tourist destination for the public, news media and politicians alike.
Amy Adams, Author providedMany scientific experiments were done there, including the excavation of large trenches and age-dating of faulted sediments. This revealed an earthquake had occurred at this location, with similar characteristics, some 22,000 to 28,000 years ago.
Evidence for this ancient quake was eroded and buried beneath the gravels of the Canterbury Plains, so the fault system evaded discovery until its rupture in 2010.
But its emergence supported prior assertions that this sparsely studied region was populated with hidden active faults that could generate earthquakes with maximum magnitudes of 7.0 to 7.2.
The existence of planning guidelines at or near active faults before the Darfield earthquake also allowed scientists to rapidly place their preliminary observations into a decision-making context.
Specifically, decisions to allow residents to rebuild in the area after the Darfield earthquake were able to be made before all scientific evidence was acquired.
From this perspective, even though the Darfield earthquake was commonly described as a surprise, it was a scenario that seismic hazard models, building codes and land-use planning guidelines had considered before it occurred.
This reaffirms some important lessons in science: uncertainty and risk are everywhere, but we can create systems and guidelines to allow us to cope with this.
And to best contribute to decision-making, scientists need to be prepared, collaborative, diverse, strategic and very efficient in how we collect and communicate scientific information to decision-makers. This can be quite demanding in the time-compressed environment of a crisis.
Complex earthquakes
By combining a range of data New Zealand scientists were the first to recognise the Darfield earthquake began on a very steep, unfavourably oriented fault that theory suggests was too inclined to rupture.
But it did rupture and cascaded from this fault (the Charing Cross Fault) on to its neighbour (the Greendale Fault) and across the fault network.
Authors: Mark Quigley, Associate Professor of Earthquake Science, University of Melbourne