Monday, March 14, 2011

Quake shifted entire island of Japan about 8 feet, sped up Earth's rotation, shortened length of day

The changes may be imperceptible to most people, but the massive earthquake that struck off the coast of Japan Friday had a startling impact on the Earth, experts say. The 8.9-magnitude quake moved Japan's main island by more than two metres, in addition to shifting Earth on its axis and briefly speeding up its rotation.

Early data from Japan suggests the earthquake moved the island about 2.4 metres (7.87 feet), according to Kenneth Hudnut of the U.S. Geological Survey. The agency compared information from a GPS station that had moved by more than two metres with satellite images from Japan.

Late Friday, scientists at NASA revealed the quake shaved more than a microsecond from the day. The quake, which lasted about two minutes, sped up the earth's rotation by about 1.6 microseconds. (One microsecond is one-millionth of a second.) NASA geophysicist Richard Gross said the quake shifted the Earth's mass, which caused the change in speed.


Over the weekend, seismologists around the world concluded that the March 11 earthquake in Japan has had a significant physical impact on the Earth.

Scientists say that the impact was so great that it moved Japan's main island, Honshu, 2.4 meters to the east, and shifted the earth on its rotational axis by almost 10 centimeters.

"Of a magnitude nine [earthquake], you would expect these values," Andreas Reitbrock, a professor of seismology at the University of Liverpool in the United Kingdom, told Deutsche Welle.

However, other scientists were a little bit more cautious at this stage.

"The displacement directly at the fault was about 15 meters, derived from seismic records," wrote Rainer Kind, a seismologist at the Helmholtz Research Centre for Geosciences in Potsdam, in an e-mail to Deutsche Welle.

"There are many GPS stations in Japan, which also measure displacement. However these data are not yet published. I suppose that the two meters displacement apply for the north-east coast of Honshu, not all of Honshu. The displacements vary certainly across Honshu, [two meters] for all of Honshu seems very much, we must wait for the GPS data."

According to Antonio Piersanti, the director of the Italy's National Institute of Geophysics and Volcanology, the quake in Japan had a greater impact on the Earth's rotational axis than the 9.1 Indonesia quake from 2004, and was second only to the massive 1960 quake in Chile.

Meanwhile, Richard Gross, a scientist at the NASA Jet Propulsion Laboratory in California, determined that the length of a single day had now been shortened by 1.8 millionths of a second.

Experts noted that previous earthquakes had a similar impact on the Earth's axis and the length of the day. The 2010 earthquake in Chile shortened the day by 1.26 millionths of a second and moved the figure axis by nearly eight centimeters.


Seismologists noted that much of the new physical detail about the Japan quake is available to scientists due to an extensive network of sensors that were placed around Japan after the 1995 tremblor in the city of Kobe.

"It gives us, for the first time, the possibility to model in great detail what happened during the rupture of an earthquake," Reitbrock said, noting that "99 percent" of global seismological data is shared on publicy accessible websites....

via Quake shifted Japan by over two meters | Science & Technology | Deutsche Welle | 14.03.2011.

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