how is sea floor spreading monitored?
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Nowadays, with GPS and diving robots, it is possible to locate where exactly certain position markers are located. Every year, North America and Europe drift apart a few centimetres, and GPS coordinates will have to add another correction. Luckily, neither North America nor the Old World as isolated systems move that fast, so that the regionalized reference systems remain valid. But if you manage to measure a location each in America and Europe to the sub-centimetre, you will notice the change in the last digits of the raw GPS coordinates within very few years.
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The hotspots are stationary.  As the overlying oceanic plate slowly moves over the hot spot, volcanic activity "pops" up through the plate, showing the relative direction of plate movement.  If the plate changes direction, you will see a bend in the line of volcanic features (called seamounts).  Look at the Hawiian islands and the Emperor Seamounts.
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SONAR (SOund Navigation And Ranging), is based on the principal that sound propagation through a liquid-based medium is reflected off of objects it hits, and when directed towards the ocean floor, it can be reflected off the bottom, shipwrecks, cracks, coral reifs, or even large fish.\n\nWhen you create a time-based map of the data, you can create a topographic relief of the ocean floor.\n\nPlease see: http://en.wikipedia.org/wiki/Sonar for more information.
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Natural resources\n\nThere is a substantial amount of petroleum and natural gas under the seabed: see North Sea oil.
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Seafloor spreading did the trick.  Wegner had the drift rate up to 100 times the actual rate, because he thought that the mechanism by which the earth's plates moved was by centrifugal force and tides.  When it was discovered that the seafloor was spreading, because the underlying material would heat up and become more plastic and allow for slippage, then the mechanism was explained and the rate of drift was brought into the right range.
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CPS( cathodic Protection System) EQUIPMENT - The system is comprised of our proprietary 32-bit Windows-based software package and associated digital underwater hardware.   CPSS is utilized in fresh, brackish, and salt water for cathodic protection surveys of structures including pipelines, outfalls, and platforms.\n\nThe system is ideally suited for underwater surveys as CPSS may be configured either as a towed fish, or attached as a sub-system interface to a remotely operated vehicle (ROV).  CPSS acquires real-time data from two CP channels with ± 5 mV accuracy, and real-time tow fish or ROV X/Y/Z coordinates from an integrated surface/subsurface navigation package.  In the tow fish configuration, the CPSS fish is towed along the pipeline route at speeds of up to 5 knots.  A precision echo-sounder is incorporated into the tow fish which enables operators to maintain the tow fish altitude within 20-feet of the seabed.  The system provides cost effective data collection on outfall or pipeline systems in up to (-) 450 FSW.  The adjacent screen capture shows the operators screen during a survey of a pipeline which is protected with impressed current with interrupters installed for the survey.
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Sea floor spreading is driven by two things. Upwelling magma from beneath the crust erupts at these spreading centers, and pressure and heat from these forms a bulge and magma pushes the plates apart.  Spreading is driven by the mass of the region around the spreading center as it increases and slides off of the bulge pushing outward. At the opposite end of the oceanic plate, there is a pulling motion, caused by colder subducting slabs sinking downward into the asthenosphere. This push-pull motion sets up a gradual motion of the seafloor outward from the mid-ocean ridges. \n\nAnother mechanism that may be contributing to this movement is what is called friction of convection. As plastic nearly-molten rock moves through the mantle is may be dragging these plates along by fricton. Since the spreading centers are likely to be upwellings of deep hot rock, the flow would be moving away from these centers under the ocean crust and pulling it away from the centers.
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seismographs and seismometers
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A spreading center. The mid-Atlantic Ridge is the most well known example of a spreading center.\n\n*Edit*\nConvergent boundaries (subduction zones) have accretion wedges, and so are also accreting plate boundaries.
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Animal behavior study. A transmitter is attached to a birds leg, a deer's neck. This helps to determine if animals move out of the habitat which they were born.\n\nUsed to record wild life in a given area, sound and pictures as animals move tripping a motion detector.\n\nEarthquake detection:\nAlso, to detect ground motion near fault lines such as in California or on volcanic mountains which may errupt. Also, detection for sulpher contamination which is another indicator.\n\nTsunami warning:\nAs a tsunami detection in the ocean. Yes, the US has used detectors as far back as in 1941. Not all countries support the need which could have saved lives if used in the India Ocean.\nCheck out the following link on buoy use for detection:
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Tectonic plates are moving.
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Seismologists can do so. They have special adapted equipment to measure the tremours of the earth with a luminograph(i'm not sure about the spelling). It is a pencil sketching graphs on paper always and when the ground trembles, there is an unevenity in the graph. Seisomologists also can see how the position of coastal plates have changed to predict earthquakes.
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They use very expensive equipment. They can send mechanical waves into the ground and break up rocks.\n\nOther ways include the following ---\n\nSeismic Exploration:\n\nExplosive\nVibrator Truck\nAire Gun - Oceanic exploration\n\nDetectors:\n\nGeophones (jugs) - land\nHydrophones - Ocean\n\nSubsurface Maps:\n\nStructural - Locates high areas (traps)\nIsopach - contour lines to show thickness of rock - estimates amount of oil or gas.
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earthquakes, tsunamis, ocean floor depressions,polar seperations, further displacement of the earth's surface.
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The magnetic striping of the seafloor is similiar on both sides of an oceanic rift.  They match up like puzzle pieces.
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Patterns of seismic activity along a fault line.\n\nScientists set up seismographs to measure this activity. Movement along faultlines is not uncommon. But we do not usually feel it b/c it is not strong enough. They, however, can detect these slight movements w/ their sensitive equipment.\n\nThere are some other signs as well. An increase in geologic activity near a faultline can give clues. Uplifting of land is one. Increases in geothermal activity may be another.
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It is very simple really, although my explanation may seem complex. This was first observed in the Pacific Ocean during World War 2.  The US Navy first noticed magnetic anomalies in the sea bed during anti-submarine operations that were using airborne magnetometers to detect submarines. They began to notice variations in the magnetic field of different areas. Oceanographers in the 1950's adapted this technology and began mapping the magnetic anomalies of the sea floor. What they found were that there were symmetric patterns of magnetic field reversals preserved in the rock of the seafloor that were in wide bands parallel to the mid-ocean ridges.  These reversals of magnetic field preserved in the seafloor correspond with reversals of the earth's magnetic field that have been taking place over time. These reversals can be dated using paleomagnetic measurements of rock samples combined with other geologic data such as fossil evidence and techniques such as potassium-argon dating. There is now a well established magnetic record of much of earth's history. These magnetic stripes along the seafloor provide excellent proof of sea floor spreading by showing that the oldest parts of the seafloor are along the ocean boundaries near subduction zones and intersections with continental plates.\n\nA very good explanation with illustrations and history is here: \nhttp://www.tectonic-forces.org/simplified.htm