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    Re: Japan earthquake speeds earth's rotation
    From: Richard B. Langley
    Date: 2011 Mar 14, 14:46 -0300

    Site displacements were actually "jerky" and one site we tracked moved  
    about 11.5 feet due to tectonic plate motion before settling back to  
    about 7.5 feet. See our results here:
    http://supersites.earthobservations.org/sendai.php#Sat3
    
    -- Richard Langley
    
    On 14-Mar-11, at 2:38 PM, Lu Abel wrote:
    
    > Fewer leap seconds in our future?
    > More impressive is that the entire main island of Japan (Honshu)  
    > moved eight feet to the east!
    > How the Japan Earthquake Shortened Days on Earth
    > SPACE.com Staff,
    > Space.com Space.com Staff,
    > space.com Sun Mar 13, 3:15 am ET
    >
    > The massive earthquake that struck northeast Japan Friday (March 11)  
    > has shortened the length Earth's day by a fraction and shifted how  
    > the planet's mass is distributed.
    >
    >
    >
    > A new analysis of the 8.9-magnitude earthquake in Japan has found  
    > that the intense temblor has accelerated Earth's spin, shortening  
    > the length of the 24-hour day by 1.8 microseconds, according to  
    > geophysicist Richard Gross at NASA's Jet Propulsion Laboratory in  
    > Pasadena, Calif.
    >
    >
    >
    > Gross refined his estimates of the Japan quake's impact � which  
    > previously suggested a 1.6-microsecond shortening of the day � based  
    > on new data on how much the fault that triggered the earthquake  
    > slipped to redistribute the planet's mass. A microsecond is a  
    > millionth of a second.
    >
    >
    >
    > "By changing the distribution of the Earth's mass, the Japanese  
    > earthquake should have caused the Earth to rotate a bit faster,  
    > shortening the length of the day by about 1.8 microseconds," Gross  
    > told SPACE.com in an e-mail. More refinements are possible as new  
    > information on the earthquake comes to light, he added.
    >
    >
    >
    > The scenario is similar to that of a figure skater drawing her arms  
    > inward during a spin to turn faster on the ice. The closer the mass  
    > shift during an earthquake is to the equator, the more it will speed  
    > up the spinning Earth.
    >
    >
    >
    > One Earth day is about 24 hours, or 86,400 seconds, long. Over the  
    > course of a year, its length varies by about one millisecond, or  
    > 1,000 microseconds, due to seasonal variations in the planet's mass  
    > distribution such as the seasonal shift of the jet stream.
    >
    >
    >
    > The initial data suggests Friday's earthquake moved Japan's main  
    > island about 8 feet, according to Kenneth Hudnut of the U.S.  
    > Geological Survey. The earthquake also shifted Earth's figure axis  
    > by about 6 1/2 inches (17 centimeters), Gross added.
    >
    >
    >
    > The Earth's figure axis is not the same as its north-south axis in  
    > space, which it spins around once every day at a speed of about  
    > 1,000 mph (1,604 kph). The figure axis is the axis around which the  
    > Earth's mass is balanced and the north-south axis by about 33 feet  
    > (10 meters).
    >
    >
    >
    > "This shift in the position of the figure axis will cause the Earth  
    > to wobble a bit differently as it rotates, but will not cause a  
    > shift of the Earth's axis in space � only external forces like the  
    > gravitational attraction of the sun, moon, and planets can do that,"  
    > Gross said.
    >
    >
    >
    > This isn't the first time a massive earthquake has changed the  
    > length of Earth's day. Major temblors have shortened day length in  
    > the past.
    >
    >
    >
    > The 8.8-magnitude earthquake in Chile last year also sped up the  
    > planet's rotation and shortened the day by 1.26 microseconds. The  
    > 9.1 Sumatra earthquake in 2004 shortened the day by 6.8 microseconds.
    >
    > And the impact from Japan's 8.9-magnitude temblor may not be  
    > completely over.The weaker aftershocks may contribute tiny changes  
    > to day length as well.
    >
    >
    >
    > The March 11 quake was the largest ever recorded in Japan and is the  
    > world's fifth largest earthquake to strike since 1900, according to  
    > the USGS. It struck offshore about 231 miles (373 kilometers)  
    > northeast of Tokyo and 80 miles (130 km) east of the city of Sendai,  
    > and created a massive tsunami that has devastated Japan's  
    > northeastern coastal areas. At least 20 aftershocks registering a  
    > 6.0 magnitude or higher have followed the main temblor.
    >
    >
    >
    > "In theory, anything that redistributes the Earth's mass will change  
    > the Earth's rotation," Gross said. "So in principle the smaller  
    > aftershocks will also have an effect on the Earth's rotation. But  
    > since the aftershocks are smaller their effect will also be smaller."
    >
    >
    >
    
    -----------------------------------------------------------------------------
    | Richard B. Langley                            E-mail:  
    lang---.ca         |
    | Geodetic Research Laboratory                  Web: http://www.unb.ca/GGE/ 
      |
    | Dept. of Geodesy and Geomatics Engineering    Phone:    +1 506  
    453-5142   |
    | University of New Brunswick                   Fax:      +1 506  
    453-4943   |
    | Fredericton, N.B., Canada  E3B  
    5A3                                        |
    |        Fredericton?  Where's that?  See: http:// 
    www.fredericton.ca/       |
    -----------------------------------------------------------------------------
    
    
    
    
    

       
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