Did that earthquake off the coast of Sumatra alter Earth’s rotation and tilt?

Did the earthquake off the coast of Sumatra that triggered the horrific tsunami on December 26, 2004, alter Earth’s rotation and tilt, as some news stories suggest?

The Sumatra earthquake released as much energy as 475 megatons of TNT. That’s some 23,000 times the energy released by the atomic bomb dropped on Hiroshima during World War II. The quake’s jolt was measured worldwide, and it had lasting effects on Earth’s rotation.

According to the US Geological Survey, computer models by Richard Gross (Jet Propulsion Laboratory) indicate that the quake shifted the continental plates enough to speed up the planet’s spin (through the conservation of angular momentum) by some 0.0000027 second per day. Yet astronomers can’t physically measure such a minute change — current technology can determine the length of a day with an accuracy of about 0.00002 second.

Earth’s tilt changed too, albeit only slightly. The quake occurred fairly close to the equator, and Gross’s models show that it changed the orientation of our planet with respect to its rotational axis by a mere 0.00082 arcsecond, or 1 inch at the North Pole. That’s negligible, because the annual “polar motion” from other causes is several hundred times larger.

— David Tytell