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03.15.11
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).
Image above: The March 11, 2011, great earthquake in Japan may have shortened the length of Earth days and shifted its axis. Image credit: NASA.
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."
Images, Text, Credits: NASA / Alan Buis / JPL.
NASA Satellite Sees Area Affected by Japan Tsunami
A new before-and-after image pair from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft shows a region of Japan's northeastern coast, northeast of the city of Sendai, which was affected by the March 11, 2011 tsunami.
Image above: A new before-and-after image pair from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) instrument on NASA's Terra spacecraft shows a region of Japan's northeastern coast, northeast of the city of Sendai, affected by the March 11, 2011, tsunami. The image at the left is from March 14, 2011; the right-hand image is from August 2008. Image credit: NASA /GSFC / METI / ERSDAC / JAROS.
The images show the coastal cities of Ofunato and Kesennuma, located about 90 kilometers (55 miles) northeast of Sendai. Ofunato has a population of about 42,000, while the population of Kesennuma is about 73,000. Areas covered by vegetation are shown in red, while cities and unvegetated areas are shown in shades of blue-gray. The image on the left was acquired on March 14, 2011; the image on the right was acquired in August 2008. When compared closely, vegetation is no longer visible in many coastal areas in the new image, particularly around Kesennuma. Scientists believe this is most likely due to the effects of the tsunami.
The images show an area located at 39.4 degrees north latitude, 141.9 degrees east longitude, and cover an area of 28 by 46 kilometers (17 by 27 miles).
For more information, see: http://www.nasa.gov/topics/earth/features/japanquake/pia13915.html and http://asterweb.jpl.nasa.gov/.
Images, Text, Credits: NASA / Alan Buis / JPL.
Tsunami Damage near Ishinomaki, Japan
The Japanese city of Ishinomaki was one of the hardest hit when a powerful tsunami swept ashore on March 11, 2011. When the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA’s Terra satellite acquired the bottom image three days later, on March 14, water still inundated the city. The top image, from August 8, 2008, shows water levels under normal circumstances.
Water is dark blue in this false-color image. Plant-covered land is red, exposed earth is tan, and the city is silver. Standing water is most evident in the flat, open places that were once fields. The most extensive flooding is around the Matsushima Air Base in the lower left corner of the image. According to news reports, several airplanes were damaged in the tsunami. The neighborhoods immediately around the airstrip are also flooded.
Dark blue fills in the spaces between buildings in sections of Ishinomaki near the harbor in the center of the image and by the river in the upper right. These areas are probably flooded. Survivors in parts of Ishinomaki were being rescued in boats, reported CNN. The large image shows additional flooding near Ishinomaki and farther south in Sendai.
Image, Text, Credit: NASA Earth Observatory image created by Jesse Allen, using data provided courtesy of NASA / GSFC / METI / ERSDAC / JAROS, and U.S ./ Japan ASTER Science Team.
Sendai Coast From Space Station
From 220 miles above Japan, an Expedition 26 crew member onboard the International Space Station took this 200mm view of the Sendai coast and southward, on March 14, three days after the one-two-punch of earthquake and tsunami.
Station Crew Photographs Sendai
From 220 miles above Japan, an Expedition 26 crew member onboard the International Space Station took this 800mm view of Sendai, and the coast mostly north on March 13. Sunglint helps to highlight the flood waters over the land, flowing out the rivers, plus the heavy oils swirling on the surface with the currents. An earthquake and subsequent tsunami hit Japan on March 11.
Images, Text, Credit: NASA.
New Fire Hits Japanese Nuclear Plant
A new fire broke out Wednesday in an already fire-damaged reactor at a crippled nuclear power plant in Fukushima, Japan.
Tokyo Electric Power Co. spokesman Hajimi Motujuku says the blaze erupted early Wednesday in the outer housing of the reactor's containment vessel. It wasn't clear if the second fire at the plant's reactor No. 4 in as many days is a new blaze, or if the first fire wasn't fully extinguished. Firefighters are trying to put out the flames. Japan's nuclear safety agency also confirmed the fire, whose cause was not immediately known.
Inside The Nuclear Reactors - Latest Problems
Tuesday's fire and an apparent explosion damaged the reactor's roof, and there are concerns that the spent fuel rods are overheating. About three hours after the blaze erupted Wednesday, Japan's nuclear safety agency said fire and smoke could no longer be seen at Unit 4, but that it was unable to confirm that the blaze had been put out.
Also Wednesday, the agency said 70 percent of the nuclear fuel rods may have been damaged at another Fukushima Daiichi reactor that was first stricken last week, triggering the crisis. "But we don't know the nature of the damage, and it could be either melting, or there might be some holes in them," said an agency spokesman, Minoru Ohgoda.
Inside The Nuclear Reactors - Normal Functioning
Desperate plant operators considered dramatic plans to stave off a meltdown in the reactor, including dumping water on it by helicopter. But plant operators worried that the water wouldn't reach the fuel rods. According to NHK television, officials at Tokyo Electric Power Co. decided a hole in the roof of the reactor was "dozens of meters" from the swimming-pool-like chamber where the spent fuel rods are overheating. So a helicopter dump, similar to putting out a forest fire, probably wouldn't reach the pool.
Moreover, officials say helicopters can't carry enough water to do the job. And Japanese Defense Ministry officials are worried about the safety of military personnel on the helicopters, according to Kyodo News. TEPCO, which operates the Fukushima power plant, is still considering the use of high-pressure fire hoses to spray cooling water into the spent fuel pool.
Inside The Nuclear Reactors - After The Quake
Radiation levels are far too high to permit workers to bring hoses anywhere near the pool's edge to re-flood it manually. U.S. nuclear safety experts agreed. David Lochbaum, director of the nuclear safety program at the Union of Concerned Scientists, says a study done for Connecticut nuclear power plants concluded that in a situation such as this one, radiation would be so intense that a worker at the pool's edge "would receive a lethal dose in something like 16 seconds."
The spent-fuel problem is a new wild card in the potentially catastrophic failure of the Fukushima power plant. Since last Friday's 9.0 earthquake, the plant has been wracked by repeated explosions in three different reactors. Some experts are now concerned that spent fuel rods may overheat in two other reactors, even though they were not in service at the time of the earthquake. Those two units, Nos. 5 and 6, have not yet reported problems.
Inside The Nuclear Reactors - Fixing The Problem
"There are accounts that they're having difficulties cooling those three spent fuel pools, and they need to regain control of that," says Lochbaum, a nuclear engineer by training. "Or as a minimum, need to be able to replace the water that may be evaporating or boiling away to prevent the water from dropping below the level of irradiated fuel in the bottom of those spent fuel pools to prevent their damage from overheating as well."
Radiation Concerns From Spent Fuel Rods
The problem at reactor No. 4 was apparently brewing for some time before Tuesday's fire. The company says the temperature of the spent fuel pool reached 183 degrees Fahrenheit on Monday — twice the normal level. It apparently went higher, but a "technical failure" prevented later readings. One concern is that the spent fuel pool may not have the radiation containment barriers that protect the reactor's fission vessel. Thus, melting fuel rods could become a significant source of radiation leakage into the environment.
Radiation levels spiked as high as 400 milliSieverts per hour at the plant's main gate during Tuesday's fire and explosion — a potentially dangerous and even fatal level if it's sustained. But the International Atomic Energy Agency (IAEA) reports the levels later dropped to much lower readings. Still, company officials evacuated all but 50 of the facility's 800 workers for their own safety. The IAEA says it's seeking "details about the status of all workers, reactors and spent fuel at the Fukushima Daiichi plant."
It is not clear how much radiation exposures increased in the 12-mile evacuation zone around the plant or beyond. Radiation levels went up transiently in Tokyo, but not to levels that pose any public health concern, officials say.
Image above: A nuclear plant specialist with the Tokyo Electric Power Co. explains the structure of a nuclear reactor at the company's Fukushima power plant during a news conference Tuesday.
The problems with spent fuel rods mean there are now two potential sources of radioactive leakage at the damaged plant. A second explosion on Tuesday in the plant's No. 2 reactor probably has caused a breach in the part of the heavy containment vessel known as the suppression chamber, or torus. That potentially allows radioactive steam or water to escape from a new route.
Previously, radioactivity emanated from controlled releases of steam in an attempt to depressurize the reactors and allow cooling seawater to be pumped in.
Images, Text, Credits: The Associated Press / AFP / Getty / Adam Cole, Andrew Prince, Maria Godoy, Stephanie d'Otreppe, Nelson Hsu / NPR / U.S. Nuclear Regulatory Commission.
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