From: Paul Doherty (pauld@exploratorium.edu)
Date: Wed Dec 29 2004 - 09:53:11 PST
Message-Id: <l0311071fbdf89f51dd1c@[192.168.112.4]> Date: Wed, 29 Dec 2004 09:53:11 -0800 From: Paul Doherty <pauld@exploratorium.edu> Subject: earth rotation
Here is what a theoretician calculates,
I await the experimental measurements.
I believe the effects will be accurately measurable.
"The deadly Asian earthquake may have permanently accelerated the Earth's
rotation--shortening days by a fraction of a
second--and caused the planet to wobble on its axis, U.S. scientists said
Tuesday.
Richard Gross, a geophysicist with NASA's Jet Propulsion Laboratory in
California, theorized that a shift of mass toward the Earth's center during
the
quake on Sunday caused the planet to spin 3 microseconds, or 3 millionths
of a second, faster and to tilt about an inch on its axis.
When one huge tectonic plate beneath the Indian Ocean was forced below the
edge of another "it had the effect of making the Earth more compact and
spinning faster," Gross said.
Gross said changes predicted by his model probably are too minuscule to be
detected by a global positioning satellite network that routinely measures
changes in Earth's spin, but said the data may reveal a slight wobble.
The Earth's poles travel a circular path that normally varies by about 33
feet, so an added wobble of an inch is unlikely to cause long-term effects,
he said.
"That continual motion is just used to changing," Gross said. "The rotation
is not actually that precise. The Earth does slow down and change its rate
of
rotation."
When those tiny variations accumulate, planetary scientists must add a
"leap second" to the end of a year, something that has not been done in many
years, Gross said.
Scientists have long theorized that changes on the Earth's surface such as
tide and groundwater shifts and weather could affect its spin but they have
not
had precise measurements to prove it, Caltech seismologist Hiroo Kanamori
said.
"Even for a very large event, the effect is very small," Kanamori said.
"It's very difficult to change the rotation rate substantially."
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