Apparently the spinning of the earth slows during certain periods due to unknown reasons and this is thought to be related to an increase in big earthquakes - especially in tropical countries

We've had the slowing period for the last five years and now it is predicted that 2018 will follow the pattern of previous slowings and we will see a dramatic spike in activity

https://www.theguardian.com/world/2017/nov/18/2018-set-to-be-year-of-big-earthquakes