论文部分内容阅读
The massive earthquake that struck northeast Japan on March 11 has shortened the length of Earths day by a fraction and shifted how the planets mass is distributed.
A new analysis of the 90magnitude① earthquake in Japan has found that the intense temblor② has accelerated Earths spin, shortening the length of the 24hour day by 18 microseconds, according to geophysicist Richard Gross at NASAs Jet Propulsion③ Laboratory in Pasadena, Calif.
Grossrefined his estimates of the Japan quakes impact — which previously suggested a 16microsecond shortening of the day — based on new data on how much the fault④ that triggered the earthquake slipped to redistribute the planets mass. A microsecond is a millionth of a second.
“By changing the distribution of the Earths mass, the Japanese earthquake should have caused the Earth to rotate⑤ a bit faster, shortening the length of the day by about 18 microseconds,” Gross told SPACE.com in an email. More refinements are possible as new information on the earthquake comes to light, he added.
The scenario⑥ is similar to that of a figure skater⑦ 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 planets mass distribution such as the seasonal shift of the jet stream⑧.
The Earths figure axis⑨ is not the same as its northsouth 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 Earths mass is balanced and the northsouth axis by about 33 feet （10 meters）.
“This shift in the position of the figure axis will cause the Earth to wobble⑩ a bit differently as it rotates, but will not cause a shift of the Earths axis in space — only external forces like the gravitational attraction of the sun, moon, and planets can do that,” Gross said.
The March 11 quake was the largest. ever recorded inJapan and is the worlds 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 Japans northeastern coastal areas. At least 20 aftershocks registering a 6.0 magnitude or higher have followed the main temblor.
注释：①magnitude：巨大、重要性；
②temblor：〈美〉地震；
③propulsion：推进；
④fault：这里指断层；
⑤rotate：（使某物）转动；
⑥scenario：（对可能出现的情况的）描述、推测；
⑦figure skater：花样滑冰运动员；
⑧jet stream：（地球高空）的急流；
⑨axis：轴、轴线、中心线；
⑩wobble：（使）摇摆、摇晃。
链接：地震相关词汇
地震 earthquake/temblor
地震学 seismology
震中 epicenter
震级 magnitude
地震强度 magnitude
余震 aftershock
自然灾害 natural disaster
海啸 tsunami
受灾者 victims
死亡人数 death toll
残骸 wreckage
幸存者 survivors
救援小组 rescue team
撤运小组 evacuation team
国际援助 international contributions
地震监控 earthquake monitoring
海啸预警系统 tsunami warning system
确认死亡 be confirmed dead
受重伤 be seriously injured
被埋在废墟下 be buried under the debris
重新安置 resettlement
防疫 epidemic prevention
捐款 donation
资料来源 中国日报
注释编辑 桑 实
责任编辑 张丹凤
A new analysis of the 90magnitude① earthquake in Japan has found that the intense temblor② has accelerated Earths spin, shortening the length of the 24hour day by 18 microseconds, according to geophysicist Richard Gross at NASAs Jet Propulsion③ Laboratory in Pasadena, Calif.
Grossrefined his estimates of the Japan quakes impact — which previously suggested a 16microsecond shortening of the day — based on new data on how much the fault④ that triggered the earthquake slipped to redistribute the planets mass. A microsecond is a millionth of a second.
“By changing the distribution of the Earths mass, the Japanese earthquake should have caused the Earth to rotate⑤ a bit faster, shortening the length of the day by about 18 microseconds,” Gross told SPACE.com in an email. More refinements are possible as new information on the earthquake comes to light, he added.
The scenario⑥ is similar to that of a figure skater⑦ 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 planets mass distribution such as the seasonal shift of the jet stream⑧.
The Earths figure axis⑨ is not the same as its northsouth 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 Earths mass is balanced and the northsouth axis by about 33 feet （10 meters）.
“This shift in the position of the figure axis will cause the Earth to wobble⑩ a bit differently as it rotates, but will not cause a shift of the Earths axis in space — only external forces like the gravitational attraction of the sun, moon, and planets can do that,” Gross said.
The March 11 quake was the largest. ever recorded inJapan and is the worlds 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 Japans northeastern coastal areas. At least 20 aftershocks registering a 6.0 magnitude or higher have followed the main temblor.
注释：①magnitude：巨大、重要性；
②temblor：〈美〉地震；
③propulsion：推进；
④fault：这里指断层；
⑤rotate：（使某物）转动；
⑥scenario：（对可能出现的情况的）描述、推测；
⑦figure skater：花样滑冰运动员；
⑧jet stream：（地球高空）的急流；
⑨axis：轴、轴线、中心线；
⑩wobble：（使）摇摆、摇晃。
链接：地震相关词汇
地震 earthquake/temblor
地震学 seismology
震中 epicenter
震级 magnitude
地震强度 magnitude
余震 aftershock
自然灾害 natural disaster
海啸 tsunami
受灾者 victims
死亡人数 death toll
残骸 wreckage
幸存者 survivors
救援小组 rescue team
撤运小组 evacuation team
国际援助 international contributions
地震监控 earthquake monitoring
海啸预警系统 tsunami warning system
确认死亡 be confirmed dead
受重伤 be seriously injured
被埋在废墟下 be buried under the debris
重新安置 resettlement
防疫 epidemic prevention
捐款 donation
资料来源 中国日报
注释编辑 桑 实
责任编辑 张丹凤