The researchers found that over the past century and a half, there have been several periods of slowing earth's speed, each lasting about five years, and, crucially, that slowdown has been accompanied by an increase in powerful earthquakes
During periods of slower earth rotation, about 25 to 30 strong earthquakes occur each year, and at other times, about 15 occur
 This led the researchers to conclude that the earth's slowing speed led to more powerful earthquakes