Quake shook Earth to core, say scientists

[emad]

The Independent
By Andrew Buncombe in Washington
30 December 2004


The quake that set off the devastating tsunami literally shook the Earth to its core, scientists believe, accelerating its rotation and shortening days by a fraction of a second. It may be necessary to add a "leap second" in years to come in order to correct the change.

Meanwhile, experts said the quake, which measured 9.0 on the Richter scale, may have shifted some small islands in the region by more than 30 metres.

Richard Gross, a geophysicist with Nasa's jet propulsion laboratory in California, said he believed a shift of mass towards the Earth's centre caused the planet to spin three microseconds - one millionth of a second - faster. It also caused the planet to tilt around 2.5cm on its axis.

" had the effect of making the Earth more compact and spinning faster," he said, saying that the changes were too slight to be detected by global positioning satellite networks.

http://news.independent.co.uk/world/science_technology/story.jsp?story=596798

[Deja Q]

1. GPS networks can't see the change but he can?

I'm confused. Computers are supposed to be much better with fine and minute details than humans.

[pmbryant]

2. Looks like he's making an educated guess

Based on some calculations he made.

--Peter

[Silverhair]

5. GPS doesn't measure the earth's surface.

It measures where a signal is in reference to a network of satellites. The earthquake had no effect on the satellites' orbits. That stayed the same. If you had a GPS device and used it before and then after the quake, at the effected island of course, it would show the change.

[Salviati]

10. I believe that they do have GPS recievers attached to bedrock

in various places, to monitor just this type of thing, though usually not so violent. I'm not sure if this is how they got this 30m figure or if they have GPS monitoring of these islands though...

[liberal N proud]

3. 30 Meters is too slight to be detected by GPS?

that is like more than 30 yards for the metrically challenged.

[pmbryant]

4. No. He's talking about any change in Earth's rotation.

His calculated millionth of a second change in Earth's rotation is too slight to be detected by GPS. That's what he seems to be saying.

--Peter

[rabid_nerd]

6. Great.. spinning faster = higher gravity

Doesn't this throw off atomic science, however slight?

[pmbryant]

7. What do you mean?

:shrug:

[Az]

8. Reverse that

Lower gravity. Acceleration outwards lowers gravity from mass.

[Salviati]

9. Well, not so much the actual gravitational force,

but it's that some of the gravitational force is "used" to make you move in a big circle as the earth rotates, the rest of it is balanced out by the "normal force", AKA the force of your ass on the chair. It can also be thought of, mathematically equivalently, in terms of a fictitious "centrifugal force" pointed away from the earth.

In any case, the whole rotation of the earth, at the equator where the effect is maximum, causes a slight decrease of the usual 9.8 and change m/s^2 of about 0.0054 m/s^2, a small, but not completely negligible amount (which is why I believe France launches it's rockets from South America...) So such a small change in the rotation of earth compared to it's normal rotation speed will have a very negligible effect...

[indigobusiness]

11. An object's gravity is not altered by centripetal force.

Earth's gravity is a relative constant, except for slight variations in mass, as meteors etc come in, and aliens etc go out. No?

[rman]

12. true, but it counteracts gravity

which explains the 'bulging' of the earth near the equator.
same effect on anything on the surface.

[James T. Kirk]

13. Ah, but was it shaken to the VERY CORE or just the core?

:P:P:P:P