SCIENTIFIC ANALYSIS:LOS ANGELES – The earthquake that killed more than 700 people in Chile on February 27th probably shifted the Earth's axis and shortened the day, a Nasa scientist said.
Earthquakes can shift hundreds of kilometres of rock by several metres, 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),” Mr Gross said yesterday. “The axis about which the Earth’s mass is balanced should have moved by 2.7 milliarcseconds (about 8cm or 3in).” The changes can be modelled, though they’re difficult to physically detect given their small size, Mr Gross said.
Some changes may be more obvious, and islands may have shifted, said Andreas Rietbrock, a professor of Earth Sciences at Liverpool University, who has studied the area impacted.
Santa Maria Island off the coast near Concepcion, Chile’s second-largest city, may have been raised six feet as a result of the latest quake, Mr Rietbrock said. He said the rocks there show evidence pointing to past earthquakes shifting the island upward in the past.“What definitely the earthquake has done is made the Earth ring like a bell,” Mr 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, Mr 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. “This small contribution is buried in larger changes due to other causes, such as atmospheric mass moving around on Earth.” – (Washington Post; Bloomberg)