我沒有看過Gross的計算,但新聞報導是這樣的:
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But while other experts charted the shift of tectonic plates and the swell of ocean waters wrought by the quake, geophysicist Richard Gross mathematically calculated the temblor’s disruption of the length of the day.
The thrust-fault quake — in which plates under the Earth’s surface moved vertically — caused mass to be redistributed, said Gross, who works at the Jet Propulsion Laboratory in La Cañada Flintridge.
“On average, the mass of the Earth got a bit closer to the rotation axis,” he said. As a result, Gross said, the planet rotates faster — “just like a spinning skater brings her arms in closer to her body to rotate faster.” When the planet rotates faster, the day shortens, he said.
Gross studies the Earth’s rotation and how it is affected by cataclysmic forces of nature. “Anything that moves mass around on the Earth I take a look at,” he said.
And it takes a mega-earthquake to attract Gross’ attention.
The magnitude 6.7 Northridge earthquake didn’t even register on the scale of throwing off the Earth’s rotation.
“I didn’t look at that earthquake,” he said. “It takes something like the Chilean or Indonesian earthquake before I look at it.”
This earthquake also shifted the axis around which the Earth rotates, Gross said.
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可見地球自轉角速度改變的原因是其轉動慣量矩陣改變了,而非其角動量在地震中發生變化。
這次地震對月地距離的影響是一個長遠效應,而不是瞬時沖量。再者,效應應該是增加月地距離,而非減小。 |