Ultima Thule

In ancient times the northernmost region of the habitable world - hence, any distant, unknown or mysterious land.

Friday, August 04, 2006

Earth's gravity changed after Sumatra quake

By Aussiegirl

I wasn't aware that gravity could vary, so I consulted a physics book I found on my shelf, and this is what I found: since the earth is not a perfect sphere and its density is not uniform, g, the acceleration due to gravity, varies from place to place on the earth's surface; at the top of a high mountain, g is less than at sea level; there is a tendency for g to increase as one goes from the equator to the poles; there are also local variations in g due to variations in the nature of the earth's crust; finally, the approximate value of g is 9.80m sec-2, and it varies by about 0.5% over the earth's surface.

United Press International - NewsTrack - Study: Earth changed after Sumatra quake

COLUMBUS, Ohio, Aug. 3 (UPI) -- U.S. scientists say they've determined Earth's gravity changed as a result of the giant 2004 Sumatran earthquake.

The discovery marked the first time scientists have used satellite data to detect changes in the Earth's surface caused by a massive earthquake.

The discovery signifies a new use for data from NASA satellites and offers a possible new approach to understanding how earthquakes work.

The 9.1-magnitude December 2004 Sumatra-Andaman earthquake in the Indian Ocean produced a tsunami that killed approximately 230,000 people, while displacing more than 1 million others.

The event followed the slipping of two continental plates under the seafloor that raised ocean bed in the region by several feet for thousands of square miles.

"The earthquake changed the gravity in that part of the world in two ways that we were able to detect," said Shin-Chan Han, a research scientist at Ohio State University. He and colleagues determined the quake triggered the massive uplift of the seafloor, changing the geometry of the region and altering previous global positioning satellite measurements of the area. And the density of the rock beneath the seafloor shifted, producing detectable gravity changes.


At 4:01 PM, Blogger Francis W. Porretto said...

The Earth's "gravity map" was one of the critical factors in the development of ICBMs. You can't hit a target many thousands of miles away with any degree of accuracy unless you:

1. Know exactly where it is;
2. Have full knowledge of the vectors of all the forces that will act on it the whole way.

So when ICBMs began to be contemplated, one of the U.S.'s immediate needs was a full geophysical mapping of the Earth, including a minutely particular mapping of the force of gravity.

Remember the International Geophysical Year? I do. And I only recently found out why it was considered so important.

At 4:51 PM, Blogger Luctor et Emergo said...

Looking for Ultima Thule, your blog came up.

I had used the words once in high school, saying "Ultima Thule!" while wagging a pencil at someone (figuratively).


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