Chile earthquake may have shortened days  
Seventh strongest quake in recorded history may have shifted Earth's axis

updated 9:11 a.m. CT, Tues., March. 2, 2010



The massive 8.8 earthquake that struck Chile may have changed the entire Earth's rotation and shortened the length of days on our planet, a NASA scientist said Monday.

The quake, the seventh strongest earthquake in recorded history, hit Chile Saturday and should have shortened the length of an Earth day by 1.26 milliseconds, according to research scientist Richard Gross at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"Perhaps more impressive is how much the quake shifted Earth's axis," NASA officials said in a Monday update.

The computer model used by Gross and his colleagues to determine the effects of the Chile earthquake effect also found that it should have moved Earth's figure axis by about 3 inches (8 cm or 27 milliarcseconds).

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).

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).

Strong earthquakes have altered Earth's days and its axis in the past. The 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).

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, Gross has said in the past.

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.

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.

Gross said his findings are based on early data available on the Chile earthquake. As more information about its characteristics are revealed, his prediction of its effects will likely change.

The Chile earthquake has killed more than 700 people and caused widespread devastation in the South American country.

Several major telescopes in Chile's Atacama Desert have escaped damage, according to the European Southern Observatory managing them.

A salt-measuring NASA satellite instrument destined to be installed on an Argentinean satellite was also undamaged in the earthquake, JPL officials said.

The Aquarius instrument was in the city of Bariloche, Argentina, where it is being installed in the Satelite de Aplicaciones Cientificas (SAC-D) satellite. The satellite integration facility is about 365 miles (588 km) from the Chile quake's epicenter.

The Aquarius instrument is designed to provide monthly global maps of the ocean's salt concentration in order to track current circulation and its role in climate change.

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Chile quake moves city 10 feet 
Powerful temblor shifts others parts of South America as well



updated 12:00 p.m. CT, Tues., March. 9, 2010

The massive 8.8 magnitude earthquake that struck Chile more than a week ago moved the city of Concepcin at least 10 feet (3 meters) to the west, seismological measurements indicate.

The violent temblor the fifth most powerful quake ever measured shifted other parts of South America as well, from the Falkland Islands (located just east of the southern tip of South America) to Fortaleza, Brazil, situated on that country's northern coast.

The quake occurred off the coast of the Maule region of Chile in one of Earth's seismic hotspots where the Nazca tectonic plate is squeezed under, or subducted below, the neighboring South American plate. Tension builds up as the plates move against each other, and earthquakes such as the one that struck Chile on Feb. 27 relieve these pent-up stresses.

The movements of the Earth during earthquakes can be measured by comparing the precise GPS locations of instruments prior to the quake and then after.

These measurements can help scientists better understand the seismic processes that control earthquakes.

"The Maule earthquake will arguably become one of the, if not the most important great earthquake yet studied. We now have modern, precise instruments to evaluate this event, and because the site abuts a continent, we will be able to obtain dense spatial sampling of the changes it caused," said Ben Brooks of the University of Hawaii and a co-principal investigator of the GPS project in Chile, called the Central and Southern Andes GPS Project, or CAP.

With the GPS measurements, the researchers have constructed a map showing the relative movement of locations after the Maule, Chile, earthquake.

Other movements around South America caused by the earthquake include:

Buenos Aires, the capital of Argentina and across the continent from the quake's epicenter, moved about 1 inch (2.5 centimeters) to the west. Chile's capital, Santiago, moved about 11 inches (28 cm) to the west-southwest. The cities of Valparaiso and Mendoza, Argentina, northeast of Concepcin, also moved significantly.

During the 6.9 magnitude 1989 Loma Prieta earthquake, which occurred along the San Andreas Fault in California, the Pacific plate moved 6.2 feet (about 2 m) to the northwest and 4.3 feet (1.3 m) upward over the North American plate.

The CAP program hopes to triple its current network of 25 GPS stations spread across the Central and Southern Andes mountains to get a better picture of the motion and deformation of Earth's crust there.

"By building new stations, the project can monitor the post-seismic deformations that are expected to occur for many years, giving us new insights into the physics of the earthquake process," said Mike Bevis of Ohio State University, who has led the CAP project since 1993 and is currently in Chile doing fieldwork.

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