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Boat Forum / Electronics / December 2004Tsunami 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 >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 [quoted text clipped - 11 lines] > > -- 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 >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. |
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