Global General

Chile quake may have shortened length of Earth day

(Xinhua)
Updated: 2010-03-03 04:38

LOS ANGELES -The magnitude-8.8 earthquake that struck Chile on February 27 might have shortened the length of an Earth day by 1.26 milliseconds, NASA scientists said.

The quake, which struck Chile on Saturday, might have changed the entire Earth's rotation and shifted the Earth's axis, NASA officials said in an update published on space.com Tuesday.

"Perhaps more impressive is how much the quake shifted Earth's axis," NASA said.

Scientists at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, the US state of California used a computer model to determine the effects of the Chile earthquake.

They found that the quake should have moved Earth's figure axis by about 3 inches (8 cm or 27 milliarcseconds).

The findings are based on early data available on the Chile earthquake, said Richard Gross, a research scientist at JPL.

The Earth's figure axis is not the same as its north-south axis, which it spins around once every day at a speed of about 1,000 mph (1,604 kph), according to NASA.

The figure axis is the axis around which the Earth's mass is balanced. It is offset from the Earth's north-south axis by about 33 feet (10 meters), NASA said.

Strong earthquakes have altered Earth's days and its axis in the past. The magnitude-9.1 Sumatran earthquake in 2004, which set off a deadly tsunami, should have shortened Earth's days by 6.8 microseconds and shifted its axis by about 2.76 inches (7 cm, or 2. 32 milliarcseconds), according to NASA.

One Earth day is about 24 hours long. Over the course of a year, the length of a day normally changes gradually by one millisecond. It increases in the winter, when the Earth rotates more slowly, and decreases in the summer.

The Chile earthquake was much smaller than the Sumatran temblor, but its effects on the Earth are larger because of its location. Its epicenter was located in the Earth's mid-latitudes rather than near the equator like the Sumatran event, according to NASA.

The fault responsible for the 2010 Chile quake also slices through Earth at a steeper angle than the Sumatran quake's fault, NASA scientists said.

"This makes the Chile fault more effective in moving Earth's mass vertically and hence more effective in shifting Earth's figure axis," NASA officials said.