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Multi-fault quakes more common than thought

Complex multi-fault earthquakes may be more common than previously thought, based on a review of data by New Zealand researchers following last year’s Kaikoura catastrophe.

Until recently each quake was expected to mainly take place on an individual fault. But the Kaikoura event was one of the most complicated recorded, and ruptured at least 17 different faults.

A team from Canterbury University, Otago University and GNS Science received $NZ67,000 ($62,600) of Earthquake Commission funding to study data from quakes dating back to 1840 and to use new 3D mapping techniques to generate improved information.

Professor Andy Nicol says research so far has found earthquakes before 1930 were recorded as mostly happening on a single fault, but after that date, when better information was available, more were shown rupturing multiple faults.

“The research makes us think that a rupture on one fault could certainly trigger ruptures in neighbouring faults, including faults we don’t know about and are unmapped,” he said.

“Therefore, complicated earthquakes may be more normal than was previously thought.”

The findings will inform how New Zealand’s National Seismic Hazard Model can better capture complex ruptures.

“Given the new data we are seeing, maybe we should be planning for a greater number of complicated multi-fault earthquakes than we currently are,” Professor Nicol said.

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