10 years after the Darfield earthquake that struck New Zealand: What have we learned?

Many of us may remember the magnitude 6.2 earthquake that struck Christchurch, New Zealand, on February 22, 2011. The earthquake killed 185 people, injured thousands, injured billions of dollars and economic losses.

But six months before that earthquake, an interconnected maze of previously unknown active faults erupted under the sedimentary plains about 20 to 80 km west of Christchurch.

This multi-fault rupture produced a magnitude 7.1 earthquake and released 13 times more energy than the Christchurch earthquake. The Darfield earthquake, named after the nearest town, shook our beds violently at 4.35 am on September 4, 2010.

There were no fatalities, but the extensive damage to land and infrastructure stimulated many scientific investigations.

Read more: New Zealand sits atop the remains of an ancient volcanic plume

Ten years on, it is useful to summarize some of the lessons learned following this.

Early discoveries

Within hours of the Darfield earthquake, scientists rushed to the scene. They found evidence of a major rupture of the Earth’s surface on Highfield Road (pictured above).

This site has quickly become a geological tourism destination for the public, news media and politicians alike.

Then-minister, Amy Adams (left), Prime Minister, John Key (center), and geologist Mark Quigley (right) discuss the Darfield earthquake in the aftermath of the Grindale Fault in September 2010. Amy Adams, author introduces

Numerous scientific experiments were conducted there, including digging large trenches and chronology of defective sediments. This revealed that an earthquake occurred at this site, with similar characteristics, about 22,000 to 28,000 years ago.

Evidence for this ancient earthquake eroded and buried beneath the gravel of the Canterbury plains, so the fault system avoided detection until it ruptured in 2010.

But their emergence supported earlier assertions that this minimally studied region was riddled with hidden active faults that could generate earthquakes of maximum magnitude from 7.0 to 7.2.

The presence of planning guidelines at or near active faults prior to the Darfield earthquake also allowed the scientists to quickly place their initial observations in the context of decision-making.

Specifically, decisions could have been made to allow residents to rebuild in the area after the Darfield earthquake before all scientific evidence was obtained.

From this perspective, although the Darfield earthquake has been described as a surprise, it was a scenario in which seismic risk models, building codes, and land-use planning guidelines considered before they occurred.

This reaffirms some important lessons in science: Uncertainty and risk are everywhere, but we can create systems and guidelines to allow us to deal with this.

To better contribute to decision-making, scientists need to be prepared, collaborative, diverse, strategic, and highly effective in how scientific information is gathered and transmitted to decision-makers. This can be very demanding in a time-pressed crisis environment.

Complex earthquakes

By combining a set of data, New Zealand scientists were the first to realize that the Darfield earthquake was started by a steep and unfavorable fault, the theory proposes that it tended to rupture.

But it was torn apart and crept from this bug (Charing Cross Fault) into its neighbor (Grendale’s fault) and crossed the fault network.

Mapbox / The Conversation, CC BY-ND

We are still fascinated by this aspect, and we have assumed that unfavorably directed faults like Charing Cross may serve as the bedrock regulating rupture behaviors for complex fault networks such as those responsible for the Darfield earthquake.

Modeling also shows that complex multi-fault ruptures such as the Darfield earthquake (and the Kaikoura earthquake in 2016) may be more common than single-fault earthquakes in these types of geologically complex regions.

This requires more careful study of how we characterize them or integrate them diversely into seismic risk models.

Earthquake hazards as a precursor

Earthquake hazards in the Darfield earthquake such as falling rocks and liquefaction were a harbinger of future dangers.

For example, my backyard in East Christchurch turned liquid for the first time in the Darfield earthquake. The Earth was liquefied repeatedly in at least nine other earthquakes over the next 16 months.

Subsequent studies revealed that liquefaction is expected to recur with equal intensity over time scales from 100 to 300 years. And the geological evidence for all of these hazards is in our landscapes before the earthquake sequence begins.

At the time of the Darfield earthquake, we did not yet have an understanding of the origins and significance of many of these hazards. Hence, they are unaware of land use planning decisions.

Major earthquake risk programs operating across New Zealand continue to help improve our understanding of it and may support decision-making in the future.

Similarly complex fault systems are found throughout the Canterbury Plains and provide similar sources of hazards. Complex earthquakes with multiple faults may be the rule, not the exception.

Read more: Satellites reveal melting of rocks beneath the volcanic zone, deep in the Earth’s mantle

Major rocky events similar to those in the 2011 Christchurch earthquakes have average return periods of 3,000 to 5,000 years. This does not mean that future events cannot happen again within a much shorter period of time.

The Darfield earthquake has sparked keen interest in using multiple geological sources to understand earthquakes. This knowledge continues to influence the course of seismology more broadly.

Combined with advances in engineering and other disciplines, this work shifts the narrative away from predicting the exact times and locations of earthquakes, which may never be possible, toward minimizing risks and enhancing our ability to adapt to future events.

Then Prime Minister John Key in front of a farm destroyed by the Darfield earthquake. Rob Griffiths / AP

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