© Martin Bernetti/AFP/Getty ImagesFirefighters searched for victims in the debris of a house in Curanipe.
The earthquake that struck Chile was so powerful it shifted the planet's axis enough to make it spin slightly faster, meaning our days will be shorter by 1.26 millionths of a second, according to preliminary calculations by scientists at the National Aeronautics and Space Administration.
"This is an esoteric effect that physics says has to happen," notes David Kerridge, the British Geological Survey's head of natural hazards, who studies earthquakes. "It's interesting, but it has no particular consequence on anything."
Scientists have long noted that just about any event that shifts a large amount of mass from one part of the planet to another will have a tiny - and sometimes measurable - effect on the Earth's rotation. Such events include changes to ocean currents, big shifts in the atmosphere, earthquakes, and possibly even the creation of more and more reservoirs from the damming of rivers.
The 8.8-magnitude temblor that struck Chile on Saturday is one of the largest quakes in a century. It was the result of an ocean tectonic plate - a shard of the earth's crust - sliding under the South American plate; over time, the two became locked together. When the pent-up energy overcame the forces of friction and the South American plate sprang upward, it unleashed a huge amount of energy in the form of the quake.
The planet was jolted to its roots. A chunk of the Earth's mass was redistributed vertically, which caused the planet's figure axis - on which the Earth's mass is balanced - to move by about three inches, according to calculations by NASA scientist Richard Gross. The net effect of that mass redistribution made the earth spin slightly faster, just as a figure skater speeds up when she pulls in her arms.
"It's important for us to know how the earth's rotation changes," said Dr. Gross, of NASA's Jet Propulsion Laboratory. "It helps us figure out where a spacecraft is and to navigate it for a precise pinpoint landing" on Mars, the moon or another planet. Dr. Gross and his colleagues had conducted a similar analysis following the even bigger 9.1-magnitude quake in Indonesia. They found that the 2004 temblor decreased the length of a day by 6.8 microseconds and shifted the North Pole by a few centimeters.
For a long time, earthquakes have been gradually changing the shape of the earth as well. Calculations suggested that the earth's oblateness - the way it is flat on top and bulges at the equator - had decreased by a tiny amount following the Indonesian earthquake. In other words, the world is getting slightly rounder.
Dr. Gross said that though the Chilean quake was less powerful than the 2004 Indonesia temblor, it likely changed the position of the figure axis a bit more. (The planet's figure axis is separate from the north-south axis; they are about 33 feet apart.)
The vertical redistribution of mass caused by the Chilean quake had a slightly greater impact in shifting the figure axis because the quake happened near the mid-latitudes, NASA concludes. Plus, the fault in Chile dips into Earth at a slightly steeper angle, which again has a greater effect on shifting the figure axis.
The Haiti quake, by contrast, didn't make the Earth wobble in quite the same way, according to Dr. Kerridge. The Haiti quake was caused by one tectonic plate sliding past another, not above or under it. "There was almost no vertical movement there when the quake happened, so you wouldn't expect the same effect," says Dr. Kerridge.
Write to Gautam Naik at gautam.naik@wsj.com
Comment: NASA scientists
claimed the Chilean earthquake shifted the Earth's axis by "2.7 milliarcseconds (about 8 centimeters or 3 inches)" and shortened the day by "1.26 microseconds (millionths of a second)". Just one strong quake, imagine! But the claim was
countered as unverifiable and ludicrous by German scientists:
Professor Rainer Kind from the German Research Centre for Geosciences (GFZ) in Potsdam said: "It is highly doubtful that these calculations are correct. The changes to the Earth's axis caused by an earthquake would be so tiny that it isn't measurable and therefore impossible to reliably detect."
Existing calculations of the movement of the Earth's axis by past earthquakes are still being debated, the expert added.
Professor Karl-Heinz Glassmeier from the Deutschen Geophysikalischen Gesellschaft (German Geophysical Association) also criticised the alleged discovery: "I hit my hand on my head as I read that yesterday.
"NASA can only make the headlines with it. A figure of eight centimetres is absolutely unverifiable."
The influence of an earthquake on the Earth's tilt would in any case be extremely low, explained Dr. Mojib Latif from The Leibniz Institute of Marine Sciences in Kiel.
He said: "The heavenly bodies around us are mainly responsible for the Earth's tilt. The gravity of the heavy and big planets in particular determines the gradient of the Earth's axis.
"That can not be changed by an earthquake, even one as powerful as that in Chile."
Professor Kind added: "It is impossible that there could ever be such a severe earthquake which would observably move the Earth's axis. That would only be possible through outside influences, for example a meteorite.
"The destruction however would be so great, that the movement of the Earth's axis would be comparatively insignificant."
So while a strong earthquake may not be sufficient to shift the planet's axis and thus alter the length of days, it's conceivable that a change in the arrangement of "the heavenly bodies" might well do so. The good professor probably didn't have this in mind when he used that term, but if we consider that comets and their debris trails are also "heavenly bodies", then we can see that earthquakes may be a symptom of an external cosmic force affecting Earth's rotation. Any slowing down of rotation, however imperceptible, would be sufficient to affect the magnetic field and produce incredible pressures within the planet that then shift tectonic plates, resulting in more earthquakes and volcanic eruptions as that pressure is released.
Comment: NASA scientists claimed the Chilean earthquake shifted the Earth's axis by "2.7 milliarcseconds (about 8 centimeters or 3 inches)" and shortened the day by "1.26 microseconds (millionths of a second)". Just one strong quake, imagine! But the claim was countered as unverifiable and ludicrous by German scientists: So while a strong earthquake may not be sufficient to shift the planet's axis and thus alter the length of days, it's conceivable that a change in the arrangement of "the heavenly bodies" might well do so. The good professor probably didn't have this in mind when he used that term, but if we consider that comets and their debris trails are also "heavenly bodies", then we can see that earthquakes may be a symptom of an external cosmic force affecting Earth's rotation. Any slowing down of rotation, however imperceptible, would be sufficient to affect the magnetic field and produce incredible pressures within the planet that then shift tectonic plates, resulting in more earthquakes and volcanic eruptions as that pressure is released.