Scientific reports from NASA and other sources indicate that Earth's spin can speed up due to certain geophysical events like earthquakes, even though other phenomena can affect its rotation.
earthquake in Chile. But its type—a thrust earthquake—counted most for Earth’s rotation. “In a thrust event, one tectonic plate slides under another, and it can move mass up or down,” Gross said. When the Nazca Plate pushed under the South American Plate and moved down towards Earth’s axis, the laws of physics dictate that Earth’s spin sped up.
Likewise, the huge 2004 Sumatran earthquake similarly rearranged the Earth’s mass, causing it to spin slightly faster. On the other hand, ice loss on Greenland in recent years may have slowed down the Earth, as meltwater flowed off its massive ice sheet and down into the ocean, moving further away from the Earth’s axis.
Such mass shifts and other events change Earth’s speed of rotation, and translate into variations as large as a millisecond in length of day, the time it takes Earth to make a complete rotation. These variations create imprecision for navigation systems that depend on Earth’s rotation, so Gross looks for ways to measure them, using extremely precise satellite data and special analysis methods. He can detect the effects of ordinary weather patterns. “The biggest causes are changes in the winds, particularly in the jet streams, which can explain 90 percent of length of day changes,” Gross said. For example, strong westerly winds can make the atmosphere speed up, and then the solid Earth must slow down its rotation. Changes from tsunamis and earthquakes have so far been too small to measure with current techniques.
Image
Image Caption
This artist’s depiction shows the Mars Rover on the surface of Mars. Because of precise information about Earth’s length of day and orientation, NASA was able to directly land the Rover on Mars. (Courtesy NASA Mars Exploration Rover Mission)
Mass-shifting events can also make the Earth wobble. “The Earth rotates around its rotation axis, but its mass is balanced about a different axis, the figure axis. Because these axes are different, the Earth wobbles as it rotates,” Gross said. E
Abstract. El Niño–Southern Oscillation (ENSO) events are classically associated with a significant increase in the length of day (LOD), with positive mountain torques arising from an east–west pressure dipole in the Pacific driving a rise of atmospheric angular momentum (AAM) and consequent slowing of the Earth's rotation. The large 1982–1983 event produced a lengthening of the day of about 0.9 ms, while a major ENSO event during the 2015–2016 winter season produced an LOD excursion reaching 0.81 ms in January 2016. By evaluating the anomaly in mountain and friction torques, we found that (i) as a mixed eastern–central Pacific event, the 2015–2016 mountain torque was smaller than for the 1982–1983 and 1997–1998 events, which were pure eastern Pacific events, and (ii) the smaller mountain torque was compensated for by positive friction torques arising from an enhanced Hadley-type circulation in the eastern Pacific, leading to similar AAM–LOD signatures for all three extreme ENSO events. The 2015–2016 event thus contradicts the existing paradigm that mountain torques cause the Earth rotation response for extreme El Niño events.