Earthquakes and the earth's rotation
Posted by JAC on 3/3/2010, 6:10 pm
Earth's rotation is impacted by many factors.

Among them are the distribution of mass and the shape of the planet.  

Both play a role in Earth's rotational speed.

The rotation of a sphere causes its equator to bulge and its poles to be drawn together.  

The shape of the Earth is nearly spherical but not quite.  

The true shape of the Earth is a spherical shape flattened at the poles and bulging at the equator called a geoide.  

Earth scientists are capable of measuring the shape of the geoide with considerable accuracy.

Earthquakes occur when large bodies within the Earth shift position.  

If there is a large landslide or shift of a block of crust toward the center of the Earth, Earth's rotational speed will increase just as a skater's rotational speed increases as arms are drawn closer to the body.  

If there is a shift of a block of Earth's crust away from the center, as has been occuring in the Himalaya mountain chain in Asia for tens of millions of years, the rotational speed will decrease.  

To use the skater analogy again, the Himalayas are a slowing outstretched arm that is slowing the skater's (Earth's)rotation.  

The Himalayas have been growing episodically and many of those episodes are marked by earthquakes such as the devasting earthquake in Pakistan last year.

Though we can measure the Earth's rotational speed by comparing the length of a day against an atomic clock, the changes in rotation caused by sudden crustal movements (earthquakes) are too small to measure accurately.
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earth loses fraction of a second. - hillsboroughweather, 3/3/2010, 2:13 pm
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