Richard Gross, research scientist at the Jet Propulsion Laboratory (JPL), calculates that the recent magnitude 8.8 earthquake in Chile was so violent that it shoved the earth’s axis a full eight centimetres from it’s original location. Additionally, the resulting change to the Earth’s Moment of Inertia would have slowed its rotation down, to make the day several microseconds longer!
Earthquakes are caused by plate tectonics. Plates grinding past each other tend to stick, and when they finally break loose, they jerk ahead to their new positions with tremendous force. The bigger the earthquake, the further the motion, and these sudden movements tend to shift the Earth’s weight around. However, Gross points out that the earth is constantly changing it’s rotation and and axis, because of far bigger movements deep within: the liquid core and mantle swirl and flow over time, dragging the planet with them! So, dramatic and tragic as the Chilean earthquake was, the planet as a whole barely felt a thing.