Planetary safetyChile Earthquake shifted Earth's axis by 3 inches
The 27 February 8.8 magnitude earthquake in Chile has shifted the Earth’s axis by three inches, causing each day to be shorter by 1.26 microseconds (a microsecond is one millionth of a second); the Earth is not a perfect sphere, with continents and oceans distributed unevenly around the planet — there is more land in the north, more water in the south; NASA scientists calculate that the Chilean quake shifted enough material to change the mass balance of the entire planet
If days feel a bit shorter these past few weeks it is because they are shorter. To be precise: 1.26 microseconds shorter. The reason: The 27 February magnitude 8.8 earthquake in Chile may have shortened the length of each Earth day, according to NASA, after shifting the earth’s axis slightly. “If our calculations are correct, the quake moved Earth’s figure axis by about 3 inches (8 cm),” according to geophysicist Richard Gross of the Jet Propulsion Laboratory in Pasadena, California.
Gross computed how Earth’s rotation should have changed as a result of the 27 February quake. Using a complex model, he and fellow scientists came up with a preliminary calculation that the quake should have shortened the length of an Earth day by about 1.26 microseconds (a microsecond is one millionth of a second), said NASA.
Perhaps more impressive is how much the quake shifted Earth’s axis. Gross calculates the quake should have moved Earth’s figure axis (the axis about which Earth’s mass is balanced) by 2.7 milliarcseconds (about 8 centimeters, or 3 inches). Earth’s figure axis is not the same as its north-south axis; they are offset by about 10 meters (about 33 feet).
According to a NASA article the reason the tilting by 3 inches is not noted is because “the figure axis defines not how Earth is tilted, but rather how it is balanced,” said Gross.
That same NASA article explained that the Earth is not a perfect sphere, with continents and oceans distributed unevenly around the planet. There is more land in the north, more water in the south, a great ocean in the west, and so on. As a result of these asymmetries, Earth slowly wobbles as it spins. The figure axis is Earth’s axis of mass balance, and the spin axis wobbles around it. “The Chilean quake shifted enough material to change the mass balance of our entire planet,” Gross said in the article.
In a separate NASA article, Gross said the same model estimated the 2004 magnitude 9.1 Sumatran earthquake should have shortened the length of day by 6.8 microseconds and shifted Earth’s axis by 2.32 milliarcseconds (about 7 centimeters, or 2.76 inches).
Gross said that even though the Chilean earthquake is much smaller than the Sumatran quake, it is predicted to have changed the position of the figure axis by a bit more for two reasons.
First, unlike the 2004 Sumatran earthquake, which was located near the equator, the 2010 Chilean earthquake was located in Earth’s mid-latitudes, which makes it more effective in shifting Earth’s figure axis. Second, the fault responsible for the 2010 Chilean earthquake dips into Earth at a slightly steeper angle than does the fault responsible for the 2004 Sumatran earthquake. This makes the Chile fault more effective in moving Earth’s mass vertically and hence more effective in shifting Earth’s figure axis.
Gross said the Chile predictions will likely change as data on the quake are further refined.
