So now, GPS measurements have confirmed a 2.4 metre (8 feet) shift of one of the GPS stations in Japan (not sure which one at this stage) …
Quote:
Kenneth Hudnut, a USGS geophysicist, said experts read data including from global positioning systems to determine the extend of the shift.
"We know that one GPS station moved (eight feet), and we have seen a map from GSI (Geospatial Information Authority) in Japan showing the pattern of shift over a large area is consistent with about that much shift of the land mass," he told CNN.
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They've also
calculated that the Earth's rotation speed has sped up by 1.6 microseconds .. slightly more than that caused by last year's Chile earthquake (8.8 Richter). Sumatra's 2004 quake (9.1 Richter), caused a 6.8 microsecond shortening of the day.
It'll be interesting to see whether measurements confirm the 1.6 microsecond increase in speed. The relationship between large quakes and the accelerated rotation speed is interesting, given that they also just recently discovered, (from seismic measurements), that the core is actually moving much slower than previously believed – approximately 1 degree every million years.
As a comparison, over the course of a year, the length of a day varies by about 1 millisecond, getting longer in the North American winter and shorter in the summer. This is thought to be mainly due to the average exchanges of energy between the solid Earth and fluid motions of Earth's atmosphere and its oceans.
Longer fluctuations of about 4 millisecs occur also, (over a 65 to 80 year cycle), and are believed to be due to flow of liquid iron in the outer core, and are measured in the magnetic field variation patterns. These fluctuations also correlate strongly with the average global surface temperature patterns.
Seems like it would take a lot of very large earthquakes, to make any appreciable impacts, when compared with the fluid movement variations.
Cheers