The periodic slowing down of the Earth’s rotation may be an early warning for increased global seismic activity, argues a paper presented at the annual meeting of the Geological Society of America in October.
Based on this finding, the researchers predict an increase in deadly earthquakes in 2018, particularly in tropical regions near the equator.
In the paper, Roger Bilham from the University of Colorado, Boulder, and Rebecca Bendick from the University of Montana, Missoula, have examined all earthquakes of magnitude 7.0 or greater since the 1900s and found five intervals during which a significantly higher number of earthquakes occurred.
The paper notes that there were between 25 to 30 high-magnitude earthquakes a year during these intervals. The rest of the time the average figure has remained around 15 major earthquakes a year.
Read more: The Science of Earthquakes
By analyzing this data, the two scientists have drawn a correlation between the slowing down of the Earth’s rotation – accompanied by a corresponding decrease in a day’s length by as much as a millisecond – and the number of high-magnitude earthquakes. They have argued that this phenomena may be linked to small changes in the behavior of the Earth’s core such as a lithospheric overshoot – a process in which the equatorial lithosphere slowly overrides the decelerating underlying mantle westward. “It is similar to the way a loose cannon would slide on the deck of a rolling ship,” the paper notes.
According to Bilham and Bendick, most of the earthquakes during intervals with high seismic activity have taken place at equatorial latitudes 10°N-30°S. Since 1900, more than 80 percent of all high magnitude earthquakes on the eastern Caribbean plate boundary took place five years after a maximum deceleration of the Earth’s rotation. This includes the Haiti earthquake of 2010 which resulted in more than 100,000 casualties.
The paper notes that the most recent episode of the periodic slowdown of the Earth’s rotation began around 2011. “This suggests that we are due to have a high number of severe earthquakes starting in 2018. This period of enhanced global seismic productivity could last at least five years,” it says.