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GPS Used To Monitor Continental Drift
metz2000 writes "BBC News is reporting that a team of scientists from Nottingham (UK) are using GPS to measure sea levels and continental drift. The team has around 50 stations across the UK, and use GPS technology to track miniscule changes in altitude and location. This allows the team to gain an understanding of how the UK landmass is likely to change over the coming centuries. They have discovered that the British Isles are tilting, with the north of the country gaining altitude and the south of the country 'sinking'."
I guess that they are using differential GPS, by which the time delay at a known location is compared to the time-delay at the location of interest. This enables for very accurate estimation of where you are.
On the other hand, at least in California (where they have a GPS network for earthquake monitoring), the network might well be permanent, hence you can do a nice sort of averaging over time. We have found that even with normal GPS, you get nice accuracies over a time period.
..in how they use GPS to make such precise measurements you can read about it here:
Using GPS to Separate Crustal Movements and Sea Level Changes at Tide Gauges in the UK
Application of the Dual-GPS Concept to Monitoring Vertical Land Movements at Tide Gauges
Whenever the offence inspires less horror than the punishment, the rigour of penal law is obliged to give way...
Back in the late 80's I had some college rooommates who did this for a living. After moderate earthquakes in southern California, groups of geophysics graduate students would be sent to the channel islands off the coast with huge old clunky GPS receivers. They would align the GPS receiver over a benchmark and camp out for 3 days collecting data. Similar groups would do the same thing all over SoCal. Combining the data makes for a super differential GPS data set. As each receiver is at a known location (well sort of, it is what they are there to determine), each has the accuracy of a single diff. GPS receiver. However, what the scientists cared about was not the aboslute positions of the receivers, but their relative positions. As I recall, 0.5cm resoultion was routinely achieved event back then. I'm sure todays systems are automated, and remotely read out. Today's grad students won't have stories about being buzzed by navy jets or herds of ferrel cats.
For continental drift, they need mm level data. I guess, they just leave the station for a longer time to get even more passes.
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They're doing very high-precision work which doesn't look at the code, but the actual waveform, using static (hours-long) occupations of benchmark monuments. Then custom software is used to work out sub centimeter (often 3-5 mm) locations in post-processing.
This sort of thing has been done in a number of locations. I've been involved with studies like this in Nevada and Italy.
It's hardly suprising that Scotland is rising and England is sinking. The phenomenon is known as 'isostatic rebound' and happens any time a substantial load is removed or added to an area. The massive ice-age glaciers over Scandinavia caused that area to sink and the 'low countries' - especially Holland - to rise. Now that the glaciers are gone, Scandinavia is rising again and the Netherlands are sinking into the sea. The same is probably happening on a smaller scale to Great Britain. In the US, the Appalachian Mountains are eroding away, causing them to rise, and the coastal plains and Mississippi delta, where that sediment is being deposited, are sinking.
This is all a very slow process, millimeters per year, but over time it makes a big difference.
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