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Science

GPS Used To Monitor Continental Drift 225

Posted by simoniker from the landmass-geocaching-over-millenia dept.
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'."
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GPS Used To Monitor Continental Drift More

GPS Used To Monitor Continental Drift

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  • Solution? (Score:4, Funny)

    by ahadley ( 665625 ) on Thursday June 05, 2003 @05:30AM (#6122054)
    well this should sort the north/south divide and tilt (apollogies for pun) the house price difference to the north.....

    just my 2 (euro) cents worth

    Alex
    • Well, what would be realy interesting is to know if the UK is drifting toward Europe or away from it. Lots of people on the continent would be interested in the answer ;-)

      • Re:Solution? (Score:3, Insightful)

        by jeremyp ( 130771 )
        From the article:

        "GPS measurements have also allowed scientists to show that the UK is drifting about 2-3 cm each year in a north-easterly direction."

        Of course you need to know what the rest of Europe is doing as well. I suspect, if it is on the same techtonic plate as Europe, then Europe is doing the same thing.
      • IIRC this question was raised when the channel tunnel was under construction, and the answer was that the UK is indeed drifting away from Europe at a rate of a few centimeters per annum. Quite how this works when we share the same tectonic plate that is fairly inactive in the region concerned I have no idea, but I'd suspect that individual plates exhibit a degree of elasticity or deform when pressure is applied to the sides.

  • Accuracy (Score:4, Interesting)

    by ewithrow ( 409712 ) on Thursday June 05, 2003 @05:31AM (#6122058) Homepage
    Considering a lot of GPS receivers have an error of + or - 10 feet or so, I wonder if they are using very precise equipment, or if having the redundancy of many units makes up for the rough estimates GPS satelites give.

    • Re:Accuracy (Score:4, Interesting)

      by Wibla ( 677432 ) on Thursday June 05, 2003 @05:32AM (#6122066)
      They are probably using the military band of the GPS sattelites, which are considerably more precise than ordinary 'civil' GPS.

      • Re:Accuracy (Score:4, Informative)

        by asmithumd ( 638830 ) on Thursday June 05, 2003 @06:39AM (#6122325)
        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.

        • Re:Accuracy (Score:3, Interesting)

          by WhiteBandit ( 185659 )
          Nope! Instead it's us sappy undergraduate students who have to do it! That is how I'll be making some money this summer in southern CA. ;)

          I think the logic is that some of the receivers are upwards of $10,000 USD, which is a very expensive toy to just have laying around, so they send groups of us students out with the receivers all day so that we basically babysit them and make sure no one touches them.

          We also have a limited amount of receivers, and a large amount of benchmarks to check, so I believe we c

      • Re:Accuracy (Score:3, Informative)

        by transient ( 232842 )
        This hasn't been true for several years. Selective availability was turned off during the Clinton administration. [ostp.gov]

    • Re:Accuracy (Score:5, Informative)

      by d-Orb ( 551682 ) on Thursday June 05, 2003 @05:35AM (#6122080) Homepage

      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.

      • Re:Accuracy (Score:3, Informative)

        by pe1rxq ( 141710 )
        They are probably not using differential gps as the base stations calculating the difference are on the very landmass they are measuring the movement off....
        They probably use a scheme similar to dgps: They don't have to know their exact location, they have to know their exact location in respect to the other measurement points around the country. Which is relativly easy to do.

        Jeroen
      • They can not use DGPS, that sends out a correction signal from a known fixed point. In this case they don't have a known fixed point, thats what they are trying to determine. The accuracy is obtained by taking many measurements over time , say 1 month, then averaging them. Its the monthly averages that are changing.
      • Well, that known location must be drifting too, so I don't think they do that. My guess is they average multiple readings to get a more accurate position, combined with military GPS.
      • There is actualy a whole bag of tricks related to DGPS that can be used, given the situation, to vastly improve relative position. Geology and cartagraphy are all about reletive position. On top of this, studies such as this one are most interested in average relative motion over long periods of time (e.g. mm/month). And this allows the use of even more tricks. This new project is not doing anything earthshaking. There have been studies like this for at least a decade. By doing a little research, one can fi

    • It depends (Score:2, Interesting)

      by k0de ( 619918 )
      GPS accuracy is somewhat consistent among manufacturers, and is generally more accurate the more you pay for the equipment. However, there is always a margin for error. For example, Wilson's GPS Accuracy page [erols.com] states that vertical accuracy depends on "latitude (errors for vertical accuracy rapidly increase with latitudes greater than 65 degrees), receiver/antenna, local geometry/multipath and satellite geometry (VDOP)"

      The real question is are the Nottingham group using high grade and control tested equipm
      • errors for vertical accuracy rapidly increase with latitudes greater than 65 degrees

        Since Cape Wrath (the northenmost point of the mainland) is only at around 58 degrees north, it'll be a wee while before our north-easterly drift takes us into the realms of 65 degrees and increasing errors.

        How trolls get modded up to interesting is beyond me.

    • Re:Accuracy (Score:4, Informative)

      by hughk ( 248126 ) on Thursday June 05, 2003 @06:50AM (#6122376) Journal
      First of all, now that Selective Availability has been disabled, stationary GPS can easily give accuracy down to a couple of metres or better. However, even when SA was enabled, surveyors could always get cm level data out of a GPS simply because they could leave the station sitting and let it average out the passes. If you are building a road, you normally want to fix it down to the cm level, because it is embarrassing when a bridge, for example, doesn't fit. Any major construction project has at least one well known point from which the land survey is based. This point connects the survey coordinate system with a general coordinate system (such as latitude and longitude from WGS84). This used to be done optically but over the last 15 years or so, GPS has been used and has performed well.

      For continental drift, they need mm level data. I guess, they just leave the station for a longer time to get even more passes.

    • Re:Accuracy (Score:3, Informative)

      by kEnder242 ( 262421 )
      I think its called differential [thalesnavigation.com] carrier phase [trimble.com] gps
      measurements below 1cm can be taken by looking at the wavelengths of the signal
    • One way to improve accuracy is to integrate thousands of measurements made over several hours. Then measure over a network of stations to reduce error. Also there are stricks like using the carrier signal for further precision.

    • Re:Accuracy (Score:4, Informative)

      by Yet Another Smith ( 42377 ) on Thursday June 05, 2003 @10:15AM (#6124035)
      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.

    • Considering a lot of GPS receivers have an error of + or - 10 feet or so, I wonder if they are using very precise equipment

      You are thinking of the consumer-grade GPS receivers, which can be had for $100 and fit in your hand. The next step up in the marketplace, for surveyors, gives ~1cm accuracy after a half hour of measurement. These cost $5000-$10000, yet are portable, but maybe are a backpack rather than handheld. The receivers and methods used in the article are obviously even better and more ex

    • They are most likely doing very long-term integration. The GPS data, while it has an inherent noise, averages out very close to a steady value over very long-term averaging.

      Regarding systematic error, they are also most likely measuring the drift of the continental plates, and would only care about the rate of change of distance (over very long time scales). So a systematic error of +/-10 feet probably doesn't matter too much.

      Scientists used a similar setup at the top of Mt. Everest to determine that

    • Surveyors don't use "real-time" GPS like navigators do -- they save the raw data from the satellites and do lots of post-processing to get millimetre accuracy (or do I mean precision?). It's called differential GPS [forinfo.biz]:

      Differential correction can reduce the effects of errors that are common to both base and roving receivers. It cannot correct for multi-path or receiver error (measurement noise) because those errors are unique to the roving receiver.

      ...

      The base and roving receivers collect GPS data at the sa

    • Re:Accuracy (Score:2, Informative)

      by joggle ( 594025 )
      The key differences are the fact that it is a network of receivers working together and that these receivers are not consumer-level. Rather, the receivers use both GPS frequencies to attain their solution. Although the second frequency isn't decoded (it's encrypted), the phase is locked on by the receiver, with the receiver simply counting the number of cyles that are received over time. With two frequencies, delays caused by weather (the troposphere) are essentially eliminated. Also, since this is a networ

  • Damn... (Score:5, Funny)

    by nmg196 ( 184961 ) on Thursday June 05, 2003 @05:32AM (#6122065)
    ...you tell me this *after* I've just bought a house in Southampton. Bummer. I knew the must be *one* good reason to live in Scotland...

    Nick...

  • accurate enough (Score:3, Interesting)

    by Naikrovek ( 667 ) <jjohnson@p[ ]com ['sg.' in gap]> on Thursday June 05, 2003 @05:32AM (#6122067)
    I didn't realize that GPS was accurate enough for that...

    I think i heard once that there were two types of recievers, one was more error prone, but gave you an updated location every second, the second was very, very accurate, but took over 10 minutes to get a position fix.

    can anyone clue me in here?
    • IANAGPSE, but Differential GPS is something that allows the resolution of millimetres by subtracting the errors of a reading from one location with the errors of a reading in another two or more locations to increase the accuracy of measurement. Near Adelaide, Australia, they have been doing this to measure the rate that the local mountain range is moving towards the city (i.e. not very quickly, but measurable using this technique.)
    • These are fixed stations. So, if it took 1 hour to make an accurate measurement, that would mean they could take 24 of them a day -- which is more than enough I would think.
    • I'll give you a hint: No one should need to need to measure continental drift every second. They're not moving apart that fast.

      • No one should need to need to measure continental drift every second. They're not moving apart that fast.

        Correction, no one wants to be in the vicinity when they're moving fast enough that measurements every second are important.

        The ground does move substantially and quickly during an earthquake.

        Proper engineering for buildings in zones prone to have earthquakes depends on knowing details of the ground acceleration spectra that are likely to be encountered. Of course, an accelerometer is likely to be a

    • There aren't two types so to speak, but there are a number of options available if you need a more accurate fix.

      First of all, all GPSs take a short while (10-300 seconds) to work out where they are when you first turn them on. How long it takes depends on a number of things:
      • How long it is since it was last switched on; More than a few hours and all the satellites will be in a different place, meaning the almanac (the orbital postitions of the satellites) will be out of date.
      • How far away from the previou
      • None of this will work however, if the US switches SA back on (Selective Availability)
        Actually SA only masks the signal if you want to get a 'quick fix'. If you are prepared to wait you get fown to the cm level even with SA enabled.

        Militarily, this isn't much use, because mostly you wouldn't want to wait a few hours for the fix to complete, standing in one position.

        • I didn't think there was any guarantee that with SA on, it would always average out to be zero over a certain unit of time? ie, can't they leave SA strayed in one direction for a very long amount of time and therefore mess up the results?
  • I think you can extrapolate this data into a correlation with population. Look at the warnings from the 1970s about halting population growth in California, especially west of the San Andreas Faultline. There were no changes, and then an earthquake strikes.

    Now the most populated area of the UK is sinking and the rest rising. If you think about it, it is quite logical. The weight of london alone is billions upon billions of tonnes, the building and auto infrastructure, not to mention several million people.
    • Who moderated this as Interesting? Please connect brain before moderating. Moderating as Funny I can maybe accept, but Interesting?

      The stuff humans account for is miniscule compared to everything else. Think of it in terms of height; human constructions are is in the range of tens of meters, not particularly dense and quite spread out, while the ground below consists of kilometers of rock. It will make no difference whatsoever, at least not by pure weight. Erosion and other effects could be significant.
    • I wonder if there might actually be a measurable effect from increased usage of groundwater in heavily populated areas. This kind of thing can cause local subsidance, so I wonder if it can cause a general shift over larger areas.

    • In related news .... (Score:4, Funny)

      by Surak ( 18578 ) * <.surak. .at. .mailblocks.com.> on Thursday June 05, 2003 @06:28AM (#6122289) Homepage Journal
      ..some scientists studying the "sinking" effect have noted CowboyNeal's recent move to Southampton.
    • naa actually big cities weigh less than the land they replace, for example Manhattan weighed more when the only buildings on it were original american villages than it does now. all that concrete and steel does weigh a lot but not as much as the earth and rock it replaced weighed.
  • Lifing at one and and sinking at the other? Where have I heard this before?

    Oh yeah, that's right... the Titanic...

  • Tilt (Score:2, Informative)

    by zbob ( 157075 )
    Sounds to me like this tilting is just the land settling down after the last ice age. The north of the country used to be covered in ice, while the south was clear. Now that the weight of the ice has gone, the land is just seeking a point of equilibrium.

    • ... is the technical term for the way that the continental plates sit on top of the oceanic plates as though they were corks in a bucket of water (only much heavier and slower).

      I was taught (only a couple of decades ago, honest!) that this sort of rebound after the ice age was supposed to be going on - in fact it was (if I remember correctly) one of the justifications for the Thames flood barrier. However, no-one (at school anyway) ever let on how this rebound was measured. It's nice to know that modern t

  • Tilting is old news (Score:2, Informative)

    by mce ( 509 )
    The fact that the northern part of Europe is rising and the southern part is sinking (for a rather broad definition of southern: Holland is sinking too), has been known for a long time. I was told in highschool (think before 1983) that this is due do the northern part having been pushed downwards during ice age(s) due to the massive weight ot the ice. When the ice last retreated, the current tilting movement was initiated.

  • Spaceborne SAR (Score:2, Interesting)

    by d-Orb ( 551682 )

    Slightly OT, but just to mention that imaging microwave radar (as those mounted in the ENVISAT or ERS satellites, for example) is also being used to monitor small changes in elevation, using a technique based on interferometric SAR (which is behind the Shuttle Radar Topography Mission [nasa.gov].

    The benefit of using a satellite orbiting around the Earth is that you don't need to deploy all the "base stations". If you want to find out more, google for "differential interferometry" or somesuch :-)

    • This technique is the volcanologists new best friend.

      Volc. A: "The new report just came in. It seems the lava dome is rising about 4cm/day. s**!"

      Volc. B: "Lets get the flock outa here NOW!"

      Volc. A: "Ok, but I need to get my laptop first."

  • This allows the team to gain an understanding of how the UK landmass is likely to change over the coming centuries.

    So, is the UK drifting west across the Atlantic, as some of paranoid us Brits fear?

  • For those interested... (Score:5, Informative)

    by heli0 ( 659560 ) on Thursday June 05, 2003 @05:48AM (#6122139)
    ..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 [nottingham.ac.uk]

    Application of the Dual-GPS Concept to Monitoring Vertical Land Movements at Tide Gauges [nottingham.ac.uk]

  • Accuracy (Score:5, Interesting)

    by ljavelin ( 41345 ) on Thursday June 05, 2003 @05:52AM (#6122149)
    From "Navigation Satellites & GPS v2.2.3 / 01 dec 02 / gvgoebel@earthlink.net /"


    Geophysicists have been exploiting GPS since the mid-1980s, using it to measure continental drift and the movement of the Earth's surface in geologically active regions. They have been able to obtain accurate surface measurements to within a few millimeters through a procedure known as "carrier tracking", which is even more accurate than differential GPS. Carrier tracking actually senses the phase of the carrier signals on which the location code sequences are broadcast. It is, not surprisingly, a tricky and subtle procedure, and not applicable for general use.
  • Ok, i understand the basic idea behind GPS. Satalites in orbit where basic geometry is used based on the subtle diffrence in the time it takes a signal to get to a device, well i'm assuming this.

    Could be useful for tracking moving things like land masses and ocean levels.

    Question: If our land masses are moving, and water moves, what ever do we actually calibrate the satalights with in the first place?

    The only thing that comes to mind is the axis of the earth. Would someone wiser then I in this area el

    • Re:Silly question... (Score:3, Informative)

      by jeremyp ( 130771 )
      This link [gps.gov.uk] has the best introduction to mapping and GPS I have ever read.
    • Not so silly. They are actually calibrated against themselves.

      Satellite (GPS & SLR) and VLBI measurements are all used to determine the relative movements of different points on the Earth (where the lasers or receivers are). The reference frame is then constructed from these point to point measurements using a "no-net rotation" constraint - any rotation of all of the stations is assumed to be a rotation of the Earth.

      It is not perfect, but it is the best we've got.

      This is coordinated by the IER

  • South is sinking? (Score:3, Funny)

    by muffen ( 321442 ) on Thursday June 05, 2003 @06:03AM (#6122191)
    .. I thought it couldn't sink any further.
    I always new there was something fishy in the south side of britain. Ah well.. atleast now they have showed that it will hit rock bottom soon :)

    Whats the point of having excellent karma if not to spend it every once in a while?
  • The results of their research makes no sense before the measurements have been conducted and analyzed over a long period of time.

    The "tilting" is just an observation of the variying stretch of an equatorial bulge, due to centrifugal force. Also, the rotational axis wobbles between 21.5 and 24.5 degrees and the GPS precision varies slightly due to moment of inertia.

    Scientists from Nottingham... Not quite.

  • Some history... (Score:2, Informative)

    by Anonymous Coward
    "They have discovered that the British Isles are tilting, with the north of the country gaining altitude and the south of the country 'sinking'"

    GREAT DISCOVERY *sarcasm*

    Since the late pleistocene the big icesheets on top of Northern Europe disappeared by global climat change from glacial to interglacial (cfr. Iversen model). As a concequence of this loss of mass on top of these plates they began to bounce back up. Imagine taking a piece of drifting wood, push it down. If you lift your finger it will rise
    • This has been known since at least the 18th century when a Swedish clergyman reported to the Swedish Academy of Sciences that "the sea was disappering slowly".

      The phenomenon in central Sweden was then and still is apparent, with an approximate uplift of 2 cm per year; in 50 years that is an uplift of one meter! This has an obvious effects for the boat traffic and harbours along the very shallow coast line of that region; the Norwegian side has steep slopes. Old coast line maps soon become outdated, borde
  • The tilt, at least, has been known for a quite a while; I remember joking with a friend from London that London might be horrible, but if we just waited a few million years the problem would be solved (we were in Scotland). That was back in the late eighties.
  • First, pardon all typos and mispellings -- its 7am and Im about to go to my second to last environmental geology classes. Its a presession class that goes for 9 days, 8a-12:30.

    Anyways, we covered plate tectonics and this movement stuff and its very interesting.

    If you need some kind of science class and you had your chem and phys in highschool and want to try something different, your university probably offers environmental geology and its an absolutely amazing class. Ive had a really easy time with it
  • This is hardly news, I was taught about this 10 years ago at school.

  • Relativity (Score:3, Interesting)

    by spakka ( 606417 ) on Thursday June 05, 2003 @07:25AM (#6122528)
    From the article:

    GPS measurements have also allowed scientists to show that the UK is drifting about 2-3 cm each year in a north-easterly direction.

    I disagree. The UK is only drifting north. Since we have no east or west pole, the east-west component of the velocity can only be stated relative to some other plate. We could just as well assert that the UK is stationary in the east-west direction, and the other plate is moving west.

    • How very British of you to declare yourself the center of the (East-West) world. ;-)

      Besides, shouldn't it be that the UK is just trying to get to the next day ever that much faster? Are we going to adjust the clocks now to account for the fact that the sun rises in Greenwich a few microseconds earlier?

    • We may not have an actual east or west pole, but we sure do have a certain good benchmark for judging. As long as the rotational speed of the Earth remains constant, and we have accurate timekeeping, and can correct for the various minor cycles and wobbles of everything, we can use the relative angles of the sun and the Earth's surface to keep longitudinal measurements consistent regardless of tectonic movement.

  • No discovery here (Score:2, Informative)

    by tagishsimon ( 175038 )
    They have discovered that the British Isles are tilting, with the north of the country gaining altitude and the south of the country 'sinking'."

    This was already common enough knowledge for those interested in the subject ... the south east & east anglia are sinking, the north west rising.

  • The sky is falling! The sky is falling!!!

    Oh--wait--the ground is rising...

    umm--nevermind :)

  • Old news (Score:2, Informative)

    by simoncrute ( 468690 )
    This seems like very old news to me.
    I seem to recall being told this in the early 1980s at school.

    Apperently it's the "rebound" effect. In the last ice age all the ice caused Scotland and Northern England to sink under it's weight.

    Since it all melted it's been slowly rising.

    I can't remember why southern England is sinking though. Maybe there's a pivet somewhere through Shefield or something ?

  • This is not new (Score:2, Informative)

    by kitty_goth ( 456618 )
    I remember an in-depth discussion of the tilting effect on the Open University in the late '80s.

  • doing this since the start of GPS @1990 (Score:3, Informative)

    by peter303 ( 12292 ) on Thursday June 05, 2003 @08:27AM (#6123013)
    Geologists have been measuring micro-motions of the earth since GPS started in the early 1990s. There are thousands of talks on the subject here [agu.org].
  • That isn't continental drift. It is selective availibility!
  • They have discovered that the British Isles are tilting, with the north of the country gaining altitude and the south of the country 'sinking'.

    They didn't discover this. The fact that the north is rising and the south sinking has been known for quite some time-- certainly longer than the GPS constellation has been up. I have a book here somewhere (can't find anything here!) that was written in the late sixties that mentions it as established fact, then positing the theory that ice age glaciers "pushed dow

  • Wasn't it like 3 feet and then improved to 1 feet? I doubt that even if they have 1cm precision, this won't be precise enough for them..?
  • FWIW, they've been doing this sort of thing in western Canada since 1991.

    www.pgc.nrcan.gc.ca/geodyn/docs/wcda_bc/content.ht m [nrcan.gc.ca]

    My first real programming job was at the Pacific Geoscience center (a decade ago), maintining the unix programs and scripts that downloaded seismic data from these remote GPS stations.

  • That would explain it, then (Score:3, Funny)

    by Epsillon ( 608775 ) on Thursday June 05, 2003 @10:24AM (#6124131) Journal

    They have discovered that the British Isles are tilting, with the north of the country gaining altitude and the south of the country 'sinking'

    That explains the difference in house prices up North and down South. I wonder when they'll start advertising southern homes as "temporary accomodation"? :o)

  • They have discovered that the British Isles are tilting, with the north of the country gaining altitude and the south of the country 'sinking'.

    Either that, or the GPS satellite positions are tilting!

  • As a continent, I find this to be a grave violation of my privacy. Can I at least opt out of this tracking?

  • I thought I would include some links to similar projects:

    SCIGN -- Southern California Integrated GPS Network
    http://www.scign.org/
    This GPS array has 250 active stations throughout SoCal continuously monitoring crustal deformation. SCIGN was started after the 1994 Northridge Earthquake and has helped the determination of the velocity field in Southern California produced by SCEC.

    An interactive map of station locations can be found at:
    http://pasadena.wr.usgs.gov/scign/Analysis/

    SCEC -- Southern California

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