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Multi-fault earthquakes – the new normal?

Multi-fault earthquakes – the new normal?

A new look at historical earthquakes is leading to fresh insights for earthquake forecasting.

Until recently, each earthquake was expected to mainly take place on an individual fault. However research led by University of Canterbury Professor Andy Nicol, and funded by the Earthquake Commission (EQC), is giving a better understanding of the movement on fault lines when earthquakes happen.

“The 2010 Darfield and 2016 Kaikoura earthquakes got our team re-looking at the history of earthquakes in New Zealand,” says Professor Nicol.

“These earthquakes ruptured multiple faults and made us suspect that earthquakes are more complicated that we used to think. The Kaikoura earthquake is one of the most complicated ever recorded globally and ruptured at least 17 different faults. So the question for our research was are these events as rare as we think, and what can we expect to happen in future earthquakes?”

Professor Nicol and the team from Canterbury University, Otago University and GNS Science received $67,000 of EQC funding to study data from earthquakes from 1840 onwards. As well as looking at all the available data, they used new 3D mapping techniques to “re-map” each earthquake’s effects and generate new seismic information.

“What we’ve found so far is that earthquakes before 1930 were recorded as mostly happening on a single fault. But there was better information after this date when most earthquakes were recorded as rupturing multiple faults.

“The research makes us think that a rupture on one fault could certainly trigger ruptures in neighbouring faults, including faults that we don’t know about and are unmapped. Therefore complicated earthquakes may be more normal than was previously thought.

“This is important because researchers look at past earthquakes to try to forecast how future earthquakes will behave. 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 says that once the team is finished their analysis, they will use their findings to help understand how future versions of New Zealand’s National Seismic Hazard Model can better capture complex ruptures. This model is used to estimate the probability of earthquakes and ground shaking in different parts of New Zealand and will help our communities prepare for seismic hazards.
Picture Caption: Google Earth image showing the many faults that ruptured during the Kaikoura earthquake.

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