Earthquake changes Earth's rotation

[George]

ABC's Diane Sawyer stated that the Earth's rotation was altered by 1.26 millionths of a second due to the Earthquake.

I found the following here (http://www.businessweek.com/news/2010-03-01/chilean-quake-likely-shifted-earth-s-axis-nasa-scientist-says.html):



This affects the Earth’s rotation, said Richard Gross, a geophysicist at NASA’s Jet Propulsion Laboratory in Pasadena, California, who uses a computer model to calculate the effects.
“The length of the day should have gotten shorter by 1.26 microseconds (millionths of a second),” Gross, said today in an e-mailed reply to questions. “The axis about which the Earth’s mass is balanced should have moved by 2.7 milliarcseconds (about 8 centimeters or 3 inches).”
The changes can be modeled, though they’re difficult to physically detect given their small size, Gross said...

Assuming the 8 cm is correct, I don't get 1.26 microseconds, but about 170 microseconds. Will someone check this out while I go out for Mexican food? :)

Also, ABC stated on the screen that the "Day shorter by 1.26 millionth/sec.". :)

I would assume that much of the rotation rate change would be nullified once the small, fortunately, tsunami bounced off the eastern shores far away.

[loupgarou]

Well, intuitively, while the tsunami was a force wave sent out from the site of the earthquake, it didn't displace the mass of the crust either north or south (to a different latitude) which would affect rotation. On the other hand, rock was displaced to a different latitude, which changes rotation.

And the tsunami is a wave and not a balancing displacement of water from one part of the world to another. Remember that a cork on the sea bobs up and down with the waves (neglecting the effect of wind) and does not otherwise change its position. Ocean waves and tsunamis are like standing waves on a string.

I also have a lot of questions about this event. Example--

If the axis of the earth is displaced, and/or if the period of the earth's rotation is changed, doesn't that affect tectonics? In other words, aren't earthquakes more likely while these new stresses are being relieved?

And aren't the currents within the mantle affected, likewise causing more earthquakes?

If the above speculation is correct, then historically there would be increased earthquake activity after major quakes--at least, where there was a north south displacement of crust.

[hhEb09'1]

George's questions are answered here, I think:
http://www.bautforum.com/universe-today-story-comments/101446-chilean-earthquake-may-have-shortened-length-day-earth.html


I also have a lot of questions about this event. Example--

If the axis of the earth is displaced, and/or if the period of the earth's rotation is changed, doesn't that affect tectonics? In other words, aren't earthquakes more likely while these new stresses are being relieved?

And aren't the currents within the mantle affected, likewise causing more earthquakes?

If the above speculation is correct, then historically there would be increased earthquake activity after major quakes--at least, where there was a north south displacement of crust.The effects of earthquakes are relatively local (increased activity because of aftershocks for instance) but in general an earthquake releases stress. The stress in the earth as a whole is not zero--the rotation axis doesn't line up with its symmetry axis, so there is an induced wobble, for instance. Studies have found that the earthquakes tend to reduce that global stress too, but it's only a tendency, not a general rule.

[loupgarou]

An earthquake releases stress, granted. But a change in the earth's axis and/or in the speed of rotation will create new stresses. At least, if the magnitude is great enough. If this conjecture is correct, then the occurrence of earthquakes (number and magnitude) worldwide will increase following the most severe quakes. Are we seeing that?

[hhEb09'1]

An earthquake releases stress, granted. But a change in the earth's axis and/or in the speed of rotation will create new stresses. At least, if the magnitude is great enough. If this conjecture is correct, then the occurrence of earthquakes (number and magnitude) worldwide will increase following the most severe quakes. Are we seeing that?We've seen some aftershocks of course, but that's local. Globally the stress is too small to create any pattern much above the usual level of earthquakes. And, as I say, earthquakes tend to relieve stress, so even if there are follow-ons, the resulting earthquakes are usually much smaller.