At www.forbes.com/sites/trevornace/2017/11/20/earths-rotation-is-mysterious… … back in 2017 we were told at Forbes that scientists think 2018 and 2019 might turn out to be years in which earthquakes were more frequent as earth's rotation has a habit of slowing down, and speeding up again. The expectation derives from a piece of research on earthquake frequency since 1900. It was found they peaked at roughly 32 year intervals. Subsequently, this was traced back to fluctuations in earth's rotation rate. Around every 25 to 30 years the earth's rotation slows down, and afterwards, increases speed once again. Around this time there is an uptick in tectonic episodes (earthquakes and volcanoes). We are of course talking about a very mild slowing down, somewhat akin to the Chandler Wobble – a residue perhaps of something more signficant in the past.
The story has been resurrected at https://tallbloke.wordpress.com/2019/12/27/forces-from-earths-spin-may-s… … forces pulling on Earths' surface as the planet spins may trigger earthquakes and eruptions of volcanoes (see also https://phys.org/news/2019-12-earth-earthquakes-volcanic-eruptions-mount… ). Seismic activity and bursts of magma on Italy's Mount Etna increases when Earth's rotational axis is furthest from its geographical axis. Earth's spin does not always line up perfectly with the north and south poles. Instead, the geographical poles sometimes twirl around like a top at Earth's rotational axis (when viewed from space). A new study in Geophysical Research Letters (2019) says this polar motion and subsequent shifts in earth's crust may increase volcanic activity. OPldbrew comments – every 25 to 20 years earth's rotation slows temporarily and this lasts for around 5 years (27 + 5 = 32). The story is also at the AGU blog = http://blogs.agu.org/geospace/2019/12/26/forces-from-earths-spin-may-spa… … and https://doi.org/10.1029/2019GL085525
The Earth's polar axis may not be as stable as mainstream insists. Is this a vestige of events in the deep past.