Sam wrote:I now understand that the earths rotation has changed due to the earthquake. Now that rattles my bones.
Yup. Lots of things operate to change the earth's rate of rotation, thereby changing the length of the day.
- Global warming melting of polar & glacial ice (earth spins faster)
- Tidal drag on the earth (braking) caused by moon & sun (earth spins slower)
- Erosion of mountains & land masses (earth spins faster)
- Earthquakes and tektonic plate motion (can go either direction)
- Seasonal global mass transport of air & water, and lunar monthly (cyclical, spinning up and down)
All of the changes above follow the law of conservation of angular momentum. It's the same principle as a spinning ice skater ... when his arms are extended he spins slowly, when he tucks them in close to his body he spins faster.
Occasionally the US Naval Observatory, the world's timekeeper, will introduce a correcting "leap second
" so that noon will not drift too far away from when the sun crosses the celestial meridian at midday.