[THS] Chilean Quake Likely Shifted Earth`s Axis, NASA Scientist Says

[Peter Webster]

http://www.bloomberg.com/apps/news?pid=20601109&sid=aLAUn4Gy92ss&pos=10

Chilean Quake Likely Shifted Earth’s Axis, NASA Scientist Says

By Alex Morales

March 1 (Bloomberg) -- The earthquake that killed more than 700 people in Chile on
Feb. 27 probably shifted the Earth’s axis and shortened the day, a National
Aeronautics and Space Administration scientist said.

Earthquakes can involve shifting hundreds of kilometers of rock by several meters,
changing the distribution of mass on the planet. 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. Some changes may be more obvious, and islands may have
shifted, according to Andreas Rietbrock, a professor of Earth Sciences at the U.K.’s
Liverpool University who has studied the area impacted, though not since the latest
temblor.

Santa Maria Island off the coast near Concepcion, Chile’s second-largest city, may
have been raised 2 meters (6 feet) as a result of the latest quake, Rietbrock said
today in a telephone interview. He said the rocks there show evidence pointing to
past earthquakes shifting the island upward in the past.

‘Ice-Skater Effect’

“It’s what we call the ice-skater effect,” David Kerridge, head of Earth hazards and
systems at the British Geological Survey in Edinburgh, said today in a telephone
interview. “As the ice skater puts when she’s going around in a circle, and she pulls
her arms in, she gets faster and faster. It’s the same idea with the Earth going
around if you change the distribution of mass, the rotation rate changes.”

Rietbrock said he hasn’t been able to get in touch with seismologists in Concepcion to
discuss the quake, which registered 8.8 on the Richter scale.

“What definitely the earthquake has done is made the Earth ring like a bell,”
Rietbrock said.

The magnitude 9.1 Sumatran in 2004 that generated an Indian Ocean tsunami
shortened the day by 6.8 microseconds and shifted the axis by about 2.3
milliarcseconds, Gross said.

The changes happen on the day and then carry on “forever,” Benjamin Fong Chao,
dean of Earth Sciences of the National Central University in Taiwan, said in an e-mail.

“This small contribution is buried in larger changes due to other causes, such as
atmospheric mass moving around on Earth,” Chao said.

To contact the reporter on this story: Alex Morales in London at
amorales2 at bloomberg.net.