According to Roger Bilham of the University of Colorado in Boulder and Rebecca Bendick of the University of Montana in Missoula, a tiny shift in the speed of the Earth’s rotation could trigger a doubling of the number of earthquakes the planet experiences.
“They believe variations in the speed of Earth’s rotation could trigger intense seismic activity, particularly in heavily populated tropical regions.
“Although such fluctuations in rotation are small – changing the length of the day by a millisecond – they could still be implicated in the release of vast amounts of underground energy, it is argued.”
The scientists studied earthquakes above a 7.0 magnitude since 1900. “Major earthquakes have been well recorded for more than a century and that gives us a good record to study,” Billham told the Observer.
In analyzing the data, they found five periods of time where the incidence of earthquakes was higher than other times. “In these periods, there were between 25 to 30 intense earthquakes a year,” said Bilham.“The rest of the time the average figure was around 15 major earthquakes a year.” These periods occurred roughly every 32 years.
In their search for correlating factors, they found these periods of higher rates of earthquakes followed a slowing of the earth’s rotation. They found that there were more large-scale seismic incidents following these five-year intervals of slowed rotations.
“It is straightforward,” said Bilham. “The Earth is offering us a five-year heads-up on future earthquakes.” In their official presentation summary, the researchers note it can be between five and six years, and the latest slowdown began in 2011, “suggesting that the world has now entered a period of enhanced global seismic productivity with a duration of at least five years.”
“The inference is clear,” Billham said. “Next year we should see a significant increase in numbers of severe earthquakes. We have had it easy this year. So far we have only had about six severe earthquakes. We could easily have 20 a year starting in 2018.”
Though it is not clear why the slowed rotation may lead to more earthquakes, Billham and Bendick believe activity in planet’s core could be involved. Science Mag explained:
“When day length changes over decades, Earth’s magnetic field also develops a temporary ripple. Researchers think slight changes in the flow of the molten iron of the outer core may be responsible for both effects. Just what happens is uncertain—perhaps a bit of the molten outer core sticks to the mantle above. That might change the flow of the liquid metal, altering the magnetic field, and transfer enough momentum between the mantle and the core to affect day length.”
The researchers’ findings ultimately only establish correlation, not causation. However, they have stirred up interest. “The correlation they’ve found is remarkable, and deserves investigation,” said Peter Molnar, another geologist the University of Colorado.
They also found most of the massive quakes related to this phenomenon have occurred near the equator.