Weekend Feature: “Japan Quake Will Shift Earth’s Mass” -NASA Expert

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NASA Jet Propulsion Laboratory’s (JPL) specialist Richard Gross has stated that following the earthquake the Earth’s figure axis (the axis around which the Earth is balanced by mass) has shifted by about 15 centimeters – 2 times greater than after the Chilean earthquake of 2010.


"According to my calculations, the length of the day should be reduced to 1.6 microseconds (millionths of a second). The earthquake in Chile gave, in my opinion, a reduction of approximately 1.2 microseconds,” he said.

According to Gross, the Earth’s axis shifted to the 139th degree east longitude. After Chilean cataclysm in 2010 it shifted to 112th degree east longitude.

The Earth has its own mass-shifting movements, according to Gross: for example, in February 2010, the Nazca tectonic plate in the eastern Pacific Ocean basin moved, causing a destructive 8.8 magnitude 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.

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 causing  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.

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.

When the oceans rise or fall, or tectonic plates move up or down, the Earth’s mass is rearranged, the figure axis changes, and the Earth starts wobbling differently. “It’s like the tire on your car; if that tire isn’t perfectly balanced, it will vibrate. The mechanic will put weights on the tire to rebalance it around its axis,” Gross said.

The Daily Galaxy via NASA

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