Scientists believe that a shift of mass toward the Earth's center during the quake caused the planet to spin 3 microseconds faster and to tilt about an inch on its axis.
LOS ANGELES, California (Reuters) -- The deadly Asian earthquake may have permanently accelerated the Earth's rotation, shortening days by a fraction of a second and caused the planet to wobble on its axis, U.S. scientists said Tuesday.
Richard Gross, a geophysicist with NASA's Jet Propulsion Laboratory in California, theorized that a shift of mass toward the Earth's center during the quake Sunday caused the planet to spin 3 microseconds, or millionths of a second, faster and to tilt about an inch on its axis.
When one huge tectonic plate beneath the Indian Ocean was forced below the edge of another "it had the effect of making the Earth more compact and spinning faster," Gross said.
Gross said changes predicted by his model probably are too minuscule to be detected by a global positioning satellite network that routinely measures changes in Earth's spin, but said the data may reveal a slight wobble.
The Earth's poles travel a circular path that normally varies by about 33 feet , so an added wobble of an inch is unlikely to cause long-term effects, he said.
"That continual motion is just used to changing," Gross said. "The rotation is not actually that precise. The Earth does slow down and change its rate of rotation."
When those tiny variations accumulate, planetary scientists must add a "leap second" to the end of a year, something that has not been done in many years, Gross said.
Scientists have long theorized that changes on the Earth's surface such as tide and groundwater shifts and weather could affect its spin but they have not had precise measurements to prove it, Caltech seismologist Hiroo Kanamori said.
"Even for a very large event, the effect is very small," Kanamori said. "It's very difficult to change the rotation rate substantially."
Scientists: Quake shifts islands
Nicobar and Simeulue farther out to sea
Tuesday, December 28, 2004 Posted: 10:28 PM EST (0328 GMT)
U.S. scientists say movement of the tectonic plates during the earthquake shifted the Nicobar Islands.
LOS ANGELES, California (Reuters) -- The massive earthquake that devastated parts of Asia permanently moved the tectonic plates beneath the Indian Ocean as much as 98 feet (30 meters), slightly shifting islands near Sumatra an unknown distance, U.S. scientists said on Tuesday.
A tsunami spawned by the 9.0-magnitude quake off the northern tip of Sumatra killed an estimated 60,000 on Sunday in Indonesia, Thailand, India, Malaysia, Sri Lanka and East Africa.
Satellite images showed that the movement of undersea plates off the northern tip of Sumatra moved the Nicobar Islands and Simeulue Island out to sea by an unknown distance, U.S. Geological Survey geophysicist Ken Hudnut said.
Although the data showed that plates more than 12 miles (20 km) beneath the ocean's surface moved dramatically, scientists will have to use handheld satellite positioning systems at the sites to learn precisely how much the land masses on the surface shifted, Hudnut said.
The USGS team in Pasadena, California, also was studying more detailed satellite images on Tuesday to determine if the scraping of one plate over another plowed up enough debris on the ocean floor to block the port of Banda Aceh in Sumatra where international aid was headed.
Large earthquakes in the last decade in Kobe, Japan, and Golcuk, Turkey, deformed the coastlines and rendered their ports inoperable after the crises, Hudnut said.
The scientists have asked for cooperation from operators of commercial satellites that can provide high-resolution images to show the extent of damage to coastlines, he said.