Darfield earthquake: lessons from the September 4, 2010 shake that triggered the Canterbury sequence

The giant Darfield quake that triggered the deadly Canterbury earthquake sequence 10 years ago today was a “wake-up call” for seismologists who have since discovered a 50 percent chance that the next major earthquake will occur on an unknown fault. .

The terrifying 7.1 magnitude earthquake that struck near the agricultural town of Darfield on the Canterbury Plains, 50 kilometers west of Christchurch, struck at 4.35am on September 4, 2010.

The violent shaking lifted the Cantabrians from their beds and caused widespread damage to land and property throughout the region.

Immediately afterwards, there was widespread relief that it arrived at such an early time in the day and resulted in no deaths.

However, it sparked thousands of aftershocks and other earthquakes, including the 2010 Great St. Stephen’s Day earthquake and the shallow disaster of February 22, 2011 that occurred at 12:51 p.m. below the city of Christchurch and killed 185 people. .

And it also resulted in groundbreaking science by New Zealand researchers trying to understand where it came from and what lessons can be learned from it.

University of Otago professor Mark Stirling said September 4 came as a surprise to the scientific community, given that it happened in an area where there were no known faults and about 120 km from the main plate boundary of the Alpine fault.

“It was a wake-up call that we have large earthquakes in these areas and they occur in characteristics that we didn’t know existed,” he said.

It became known as the Greendale Fault. Studies by the University of Canterbury and GNS found that it was last broken between 20,000 and 30,000 years ago.

New Zealand scientists, including Stirling, began looking at the country’s earthquake records dating back to 1840 and plotting how many surprises. The results were “shocking,” Stirling said, as about 50 percent of all major New Zealand earthquakes were recognized as unknown faults.

“We have recognized that there is a lot of work to do to try to improve the detection of these sources of earthquakes before they occur,” said Stirling, president of the Otago Earthquake Science Group.

Research on New Zealand’s “sleeping giants” has been closely followed by other earthquake-prone nations, including the United States and Japan.

It has also driven studies in other areas of New Zealand, including Auckland, Waikato, Otago and Southland, to try to find potential sources of active faults.

And while some of the faults are likely to break only every 10,000 years or more, Stirling said New Zealanders should remember that events are “low probability, high consequence.”

All the research generated by the 2010/11 Canterbury earthquake sequence is now helping to update the National Seismic Hazard Model, which calculates the probability and strength of an earthquake occurring in different parts of New Zealand.

Darfield’s legacy meant the country was now in a scientifically better place to understand future earthquakes, Stirling said.

“It is never good to have a big earthquake, particularly in a populated area, and then have a sequence of earthquakes that was deadly, very tragic, but the lessons learned, the awareness acquired at the scientific, engineering and public levels have been incredibly valuable. “