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10th anniversary of the magnitude 7.1 Darfield earthquake in Canterbury

This Friday marks the tenth anniversary of the magnitude 7.1 Darfield earthquake in Canterbury.  Former leader of the Natural Hazards and Risks Theme at GNS Science, Dr Kelvin Berryman, offers some thoughts on the earthquake and its ramifications.   

The rupture of a previously unknown fault west of Christchurch not only jolted Cantabrians awake on that Saturday morning in September 2010, but it was felt across the whole of New Zealand. 

Soon after daybreak, scientists from many parts of New Zealand started descending on the area with specialist equipment to gather as much information as they could about the rupture to understand this rare event and its ramifications for Canterbury and the rest of New Zealand.

“The main priorities for the scientists first on the scene were to map the fault rupture, understand its complexity, and accurately record the rich aftershock sequence,” says Kelvin Berryman, who led the science liaison with Canterbury response agencies in 2010 and 2011 and is now retired from GNS Science.

“It became evident that the Greendale Fault - as it became known - had not ruptured for at least 20,000 years. It turned out to be a very complex set of near simultaneous ruptures involving a network of up to eight small adjacent faults. But this wasn’t immediately apparent – it only became clear after some weeks of detailed investigation.” 

Thanks to the national monitoring network operated by GNS Science’s GeoNet project, the quake produced an unprecedented amount of high quality data that proved invaluable to the science community in the months following the earthquake. 

Aftershocks are a valuable diagnostic tool for scientists and after a large quake they act quickly to install temporary networks of seismic instruments surrounding the earthquake region. So within days of the quake, GNS Science through its GeoNet project, had deployed a dense network of seismographs in Canterbury to record aftershocks and GPS instruments to record any post-quake deformation of the Earth’s crust. 

Among the scientific innovations that came with the Darfield earthquake were aftershock forecasts.

GNS Science updated the forecasts daily to start with, and as the aftershock sequence gradually started to lose energy the updates became less frequent. Currently they are updated annually. 

In the months following the quake, the forecasts became an integral part of the Canterbury response and the rebuilding effort. Aftershock forecasts are now a regular part of GNS Science’s response after every major earthquake.     

Main scientific outcomes

The main scientific results stemming from the Darfield quake have been an understanding of the complexity of the rupture and the extent and severity of liquefaction damage, even though it was only a forerunner to the much more severe damage from the subsequent quakes on 22 February 2011 and 13 June 2011. 

“The Darfield earthquake also showed that rare events - once every 20,000 or 30,000 years - have to happen sometime. Low hazard does not mean no hazard.”

The long series of aftershocks provided new data to help understand how quakes can cluster. It has also provided scientists with an opportunity to test various models on how quakes can trigger one another, Dr Berryman says. 

A major area of research in the wake of both the Darfield and Christchurch quakes has been on societal and business impacts. Case studies have identified the characteristics of community and business resilience that go beyond ‘earthquake specific’.  This understanding has applications not just in New Zealand, but also internationally. 

“Another major outcome from the extended quake sequence has been the importance of a good scientific basis for managing response and recovery activities. National conversations about earthquake-prone buildings, maintaining in-ground infrastructure, land use planning, and science communication, have all been driven from the Canterbury experience.” 

There has also been a huge amount learned about liquefaction and this is being incorporated into risk management around New Zealand. 

“Another post-Darfield feature has been an improved joining together of science and policy in relation to natural hazard risks in New Zealand.” 

Looking ahead

Earthquake activity in Canterbury remains higher in the aftershock region than it was prior to 4 September 2010. The region is likely to continue to experience aftershocks for many years. 

“Scientists draw parallels with the Buller region which has had an elevated level of earthquake activity since the 1929 magnitude 7.8 Murchison quake. As recently as the early 1990's several magnitude 6 quakes occurred in the lower Buller Gorge, more than 60 years after the initiating event in 1929,” Dr Berryman says. 

The Canterbury experience has confirmed that cohesive communities where people know their neighbours, where the vulnerable are identified and supported, and where community leaders are empowered, result in a high level of resilience to whatever nature throws at us, Dr Berryman says. 

The fundamental message to Canterbury residents is still – ‘be prepared’. The level of earthquake hazard in Canterbury continues to be higher than prior to the Darfield earthquake and is similar to that faced by Nelson and Marlborough. 

“Being prepared should be a personal, family, community and business priority. Businesses that develop a good risk management approach bounce back from adversity better and are invariably more successful in 'peacetime' as well.” 

ENDS 

Note: GeoNet is a collaboration involving EQC, GNS Science and Land Information NZ.