Tsunami Effect on GPS?
 

I was watching the NBC nightly news tonight and they stated that the
rotation of the Earth was effected by the tsunami. According to the report
the day of the tsunami was slightly shorter than standard day, which would
mean that the roation increased slightly. They didn't state if the
rotational change was permanent of a 1 time event.

I was wondering if this induced an error in GPS positioning as the Earth
isn't where it is expected to be. In my way of thinking we shifted
slightly easterly. I have no idea how much of a change this is, or even if
it's measurable withn the error of a GPS, but it's an interesting question.

-- Geoff

"Geoff Schultz" wrote in message
7...
I was watching the NBC nightly news tonight and they stated that the
rotation of the Earth was effected by the tsunami. According to the
report
the day of the tsunami was slightly shorter than standard day, which would
mean that the roation increased slightly. They didn't state if the
rotational change was permanent of a 1 time event.

I was wondering if this induced an error in GPS positioning as the Earth
isn't where it is expected to be. In my way of thinking we shifted
slightly easterly. I have no idea how much of a change this is, or even
if
it's measurable withn the error of a GPS, but it's an interesting
question.

-- Geoff

I had heard a CNN comment that the quake "has changed the geography of the
globe" and they then went on to explain that the NW tip of Sumatra "may have
shifted up to 160 feet." OK, that's two degrees of weasel-words ("may have"
and "up to"), and I find a 160-foot lateral shift to be incredible. IIRC,
they also said that the Earth's rotation was slowed by 10 milliseconds per
day. That's not very much, only about one part in 864,000. or about
0.00001%.

However, if the Earth's rotation has been affected, the GPS system would be
corrected within a day or so (maybe quicker). The satellites are
continuously monitored for orbital deviations by checking the results of
positions of benchmarks. I think the satellites are corrected on every
orbit, or at least some relatively frequent schedule.

At first, you might think this was just a one-day aberration, but if you
redistribute enough mass on our rotating globe, you should be able to make
permanent changes in the rotational velocity. And that makes me think it
might be a permanent change (permanent until the next big mass
redistribution event).

Where's an orbital mechanic when you need one?

Ed
wb6wsn

On Wed, 29 Dec 2004 03:44:28 -0800, "Ed Price"
wrote:

At first, you might think this was just a one-day aberration, but if you
redistribute enough mass on our rotating globe, you should be able to make
permanent changes in the rotational velocity. And that makes me think it
might be a permanent change (permanent until the next big mass
redistribution event).

I believe you are right. If a chunk of crust was subsumed into the
mantle (i.e. "went down and got melted"), this would increase the
rotation of the earth fractionally in the same way a skater doing a
spin increases her rotation as she draws her arms tight toward her
chest (same mass rotating in a smaller radius).

By the same token, a sufficiently large volcanic event that pushed a
lot of magma to the surface would fractionally SLOW the earth's
rotation, and likely produce even more navigational hazards and
Notices to Mariners. G

The earth's rotation has been slowing due to gravitational/tidal drag
since its creation, and the moon is creeping ever farther away.

Give it enough time, and tides will drop and total eclipses will
become impossible. I, however, don't expect to be sailing then G.

I often think that going back in a time machine wouldn't be
interesting for the biology (very little on land before 300 million
years ago anyway), but for the astronomy: a 20 hour day and the
biggest moon you'll ever see. Highest tides, no doubt, as well.

R.