Endangered Earth
Subduction Zone - Japan
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The 2011 Japan Tsunami Was Caused
By Largest Fault Slip Ever Recorded
Clay lubricated the fault zone in the Japan trench, producing the devastating tsunami, researchers say.
By Jane J. Lee, National Geographic



A ship washed ashore during the 2011 Japan tsunami lies amidst wreckage in Kesennuma, Miyagi, Japan.
PHOTOGRAPH BY SANKEI VIA GETTY IMAGES


The largest fault slip ever recorded produced the devastating 2011 Japan tsunami, according to three studies published today.

Two years ago, the sea off the coast of Japan reared up and swept away tens of thousands of lives in a devastating natural disaster.

The 2011 earthquake has been the subject of intense study ever since, and the trench that produced it is the best studied in the world. (See "Japan Tsunami: 20 Unforgettable Pictures.")

Now, three papers published today in the journal Science reveal the magnitude 9 earthquake off the east coast of Japan still has the capacity to surprise.

Experts calculate the fault—or the boundary between two tectonic plates—in the Japan trench slipped by as much as 164 feet (50 meters). Other similarly large magnitude earthquakes, including the 9.1 Sumatra event in 2004, resulted in a 66-to-82 foot (20-to-25 meter) slip in the fault.

"We've never seen 50-meter [slips]," said Kelin Wang, a geophysicist with the Geological Survey of Canada in British Columbia.


Largest Fault Slip Ever Recorded - National Geographic
Quake moved Japan coast 8 feet, shifted Earth's axis
By Kevin Voigt, CNN



Images released by NASA show Japan's northeast coast before, left, and after flooding from the quake-induced tsunami.

(CNN) -- The powerful earthquake that unleashed a devastating tsunami Friday appears to have moved the main island of Japan by 8 feet (2.4 meters) and shifted the Earth on its axis.

"At this point, we know that one GPS station moved (8 feet), and we have seen a map from GSI (Geospatial Information Authority) in Japan showing the pattern of shift over a large area is consistent with about that much shift of the land mass," said Kenneth Hudnut, a geophysicist with the U.S. Geological Survey (USGS).

Reports from the National Institute of Geophysics and Volcanology in Italy estimated the 8.9-magnitude quake shifted the planet on its axis by nearly 4 inches (10 centimeters).

Quake moved Japan coast 8 feet, shifted Earth's axis - By Kevin Voigt, CNN
Japan Quake May Have Shortened Earth Days, Moved Axis




The March 11, magnitude 9.0 earthquake in Japan may have shortened the length of each Earth day and shifted its axis. But don't worry—you won't notice the difference.

Using a United States Geological Survey estimate for how the fault responsible for the earthquake slipped, research scientist Richard Gross of NASA's Jet Propulsion Laboratory, Pasadena, Calif., applied a complex model to perform a preliminary theoretical calculation of how the Japan earthquake—the fifth largest since 1900—affected Earth's rotation. His calculations indicate that by changing the distribution of Earth's mass, the Japanese earthquake should have caused Earth to rotate a bit faster, shortening the length of the day by about 1.8 microseconds (a microsecond is one millionth of a second).

The calculations also show the Japan quake should have shifted the position of Earth's figure axis (the axis about which Earth's mass is balanced) by about 17 centimeters (6.5 inches), towards 133 degrees east longitude. Earth's figure axis should not be confused with its north-south axis; they are offset by about 10 meters (about 33 feet). This shift in Earth's figure axis will cause Earth to wobble a bit differently as it rotates, but it will not cause a shift of Earth's axis in space—only external forces such as the gravitational attraction of the sun, moon and planets can do that.

Both calculations will likely change as data on the quake are further refined.

In comparison, following last year's magnitude 8.8 earthquake in Chile, Gross estimated the Chile quake should have shortened the length of day by about 1.26 microseconds and shifted Earth's figure axis by about 8 centimeters (3 inches). A similar calculation performed after the 2004 magnitude 9.1 Sumatran earthquake revealed it should have shortened the length of day by 6.8 microseconds and shifted Earth's figure axis by about 7 centimeters, or 2.76 inches. How an individual earthquake affects Earth's rotation depends on its size (magnitude), location and the details of how the fault slipped.

Gross said that, in theory, anything that redistributes Earth's mass will change Earth's rotation.



"Earth's rotation changes all the time as a result of not only earthquakes, but also the much larger effects of changes in atmospheric winds and oceanic currents," he said. "Over the course of a year, the length of the day increases and decreases by about a millisecond, or about 550 times larger than the change caused by the Japanese earthquake. The position of Earth's figure axis also changes all the time, by about 1 meter (3.3 feet) over the course of a year, or about six times more than the change that should have been caused by the Japan quake."

Gross said that while we can measure the effects of the atmosphere and ocean on Earth's rotation, the effects of earthquakes, at least up until now, have been too small to measure. The computed change in the length of day caused by earthquakes is much smaller than the accuracy with which scientists can currently measure changes in the length of the day. However, since the position of the figure axis can be measured to an accuracy of about 5 centimeters (2 inches), the estimated 17-centimeter shift in the figure axis from the Japan quake may actually be large enough to observe if scientists can adequately remove the larger effects of the atmosphere and ocean from the Earth rotation measurements. He and other scientists will be investigating this as more data become available.

Gross said the changes in Earth's rotation and figure axis caused by earthquakes should not have any impacts on our daily lives. "These changes in Earth's rotation are perfectly natural and happen all the time," he said. "People shouldn't worry about them."

Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

NASA 2011-080

Japan's Tsunami: How It Happened (1 of 5)















Uploaded on Apr 3, 2011
Japan's Tsunami: How It Happened , investigates the science behind the earthquake and tsunami that has devastated Japan. It takes viewers on a journey with Professor of Geological Sciences Roger Bilham -- in Japan only days after the earthquake struck. The programme follows Roger as he sets off on a mission to view the devastation from the air. In the magnitude 9 earthquake Japan shifted a full 12 feet towards the US.
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