The magnitude 8.8 quake that slammed central Chile February 27 knocked the entire planet for a loop — literally. The sudden, large-scale movement of tectonic plates that triggered the quake shifted immense masses of rock a few meters closer to Earth’s core, tilting the planet’s axis a few centimeters and imperceptibly shortening the day, analyses indicate.
Disaster struck just after 3:34 a.m. local time, when seismic stresses that had been building for decades, if not centuries, let loose. Rocks along the interface between two tectonic plates slipped past each other a distance of seven to 11 meters, says Jian Lin, a geophysicist at the Woods Hole Oceanographic Institution in Massachusetts.
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The movement of tectonic plates in Chile February 27 has triggered glitches in Earth’s rotation, a new analysis suggests. Sudden subduction of the Nazca plate carried large amounts of mass closer to the center of the Earth — which, conceptually but on a vastly different scale, works like spinning skaters bringing their arms closer to their bodies, says Richard Gross, a geophysicist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif. As a result, Earth’s day is now about 1.26 microseconds shorter than it was before the massive quake, Gross estimates.
And because the quake’s shift in mass occurred deep in the Southern Hemisphere, Earth was slightly tipped off balance — a result similar to a spinning skater bringing in one arm but not the other. The planet’s “figure axis,” the line about which the Earth is balanced, shifted about 8 centimeters, Gross notes.
Earth’s axis is constantly wobbling at various frequencies, with some oscillations measuring several meters and taking months to unfold. Forces driving those cycles, including those resulting from winds and ocean currents, act continually across Earth’s surface and often are about a thousand times larger than those generated during the Chilean quake.
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