Nature says the earthquake prophet is IN. Or in the machine at least. For the first time, a machine-learning system beat human experts at figuring out where tremors would hit following a big quake:
“We’ve really just scratched the surface of what machine learning may be able to do for aftershock forecasting,” says Phoebe DeVries, a seismologist at Harvard University in Cambridge, Massachusetts. She and her colleagues report their findings1 on 29 August in Nature.
Aftershocks occur after the main earthquake, and they can be just as damaging — or more so — than the initial shock. A magnitude-7.1 earthquake near Christchurch, New Zealand, in September 2010 didn’t kill anyone: but a magnitude-6.3 aftershock, which followed more than 5 months later and hit closer to the city centre, resulted in 185 deaths.
Seismologists can generally predict how large aftershocks will be, but they struggle to forecast where the quakes will happen.
The scientists looked at more than 131,000 mainshock and aftershock earthquakes, including some of the most powerful tremors in recent history, such as the devastating magnitude-9.1 event that hit Japan in March 2011. The researchers used these data to train a neural network that modelled a grid of cells, 5 kilometres to a side, surrounding each main shock. They told the network that an earthquake had occurred, and fed it data on how the stress changed at the centre of each grid cell. Then the scientists asked it to provide the probability that each grid cell would generate one or more aftershocks. The network treated each cell as its own little isolated problem to solve, rather than calculating how stress rippled sequentially through the rocks.
When the researchers tested their system on 30,000 mainshock-aftershock events, the neural-network forecast predicted aftershock locations more accurately than did the usual stress-failure method. Perhaps more importantly, DeVries says, the neural network also hinted at some of the physical changes that might have been happening in the ground after the main shock. It pointed to certain parameters as potentially important — ones that describe stress changes in materials such as metals, but that researchers don’t often use to study earthquakes.
The findings are a good step towards examining aftershocks with fresh eyes, says Daniel Trugman, a seismologist at the Los Alamos National Laboratory in New Mexico.