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March 5, 2010 / Dave Gorham

Quake Shortens Days

Last week’s Chilean earthquake was the seventh strongest earthquake in the known history of the world (actually, at 8.8 magnitude, it ties the 1906 earthquake off the coast of Ecuador). It was so strong that it actually shifted the Earth’s figure axis (axis around which the Earth’s mass is balanced and perhaps confused with the Earth’s north-south rotational axis; the difference between the two being about 33 feet). Based on computer models, the shift in mass should have shortened the time it takes the Earth to make one rotation about its axis by 1.26 milliseconds and shifted the figure axis by as much as three inches. Typically, the normal cycle of the Earth’s rotation can change by one millisecond over the course of a year.

Interestingly, stronger quakes have not had the same affect. Due to their location closer to the Equator, stronger quakes have had less of an impact on the Earth’s axis than the February 27 mid-latitude Chilean quake centered at 35.846 South latitude, 72.719 West longitude. In addition, last week’s quake struck along a deeper and more sharply angled fault than, for instance, the 9.0 magnitude quake of 2004 near Sumatra. By contrast, the Sumatra quake shifted the axis 2.76 inches. According to NASA officials, the location and steepness of the quake and fault make it more effective at moving the Earth’s mass, therefore more effective at shifting the Earth’s figure axis and, in this case, allows the Earth to spin ever so slightly faster.


Earth’s axial or obliquity tilt. Image: Wiki

The 2010 Chilean Earthquake centered about 200 miles southwest of Santiago, Chile. Image: Wiki





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