Serc.carleton.edu



Plate Motion and GPS measurement – Oct 2, 2008

Earth Exploration Toolbook

The chapter has some back-ground material about plate movement, and global positioning system measurements (GPS) from satellites to hand-held instruments. In addition, more information could be found by doing a search on the National Science Digital Library website () using search term “plate motion” or using the Digital Library for Earth Systems Education (DLESE) at – maybe filtered to K-12 education. Some results below:

plate movement calculator

plate motion and hot spots

a “book” online – middle school portal USGS

Some of the numbers asked to be calculated in the SEAT station motion calculations:

Fit a line to the North movement values from 2004 to present in 2008.

The graph of values in Excel had a trendline as an option and when you chose a linear fit (the default) and requested an “option” of display equation on the graph, you get a y = mx + b equation where the m is the velocity of the movement, to the north in this case. The m value is .0091 mm/day since the graph is a fit of daily average change in position from a fixed reference point. (from physics, distance per time is called velocity, or rate) To compute the velocity for a year, multiply by 365.25 days in a year.

.0091 * 365.25 = 3.32 mm/yr to the north

Similarly for the East direction, a linear fit (trendline with equation displayed) gives a slope value of .0108. Multiplying by 365.25 to get yearly movement

,0108 * 365.25 = 3.9447 to the East.

The angle values created by setting up a vector of length 3.32 vertically and 3.94 horizontally, are 40 degrees up from the x – axis, Or 90-40 = 50 degrees down from the North direction. Measurement from North is the conventional way to express the angle direction for many things – ship position on the sea and plate movement being two examples.

Using the trig keys on a calculator, Arctan (3.32/3.94) = 40 degrees

The length of the resultant of the two perpendicular forces is a vector 5.16 mm.

This is found using the Pythagorean theorem.

SQRT[ (3.32)**2 + (3.95)**2 ]= 5.16 mm/yr

So the SEAT station has moved about 5.16 mm/yr at an angle of 50 degrees from North.

If you were to look at a station on the coast, you would find the direction to be roughly the same, but the vector length about 3 times longer. For PABH station, I calculated about 17.76 mm/ yr from data for 2004 to 2008. This has moved “faster” than the location further inland.

A participant in our session suggested that he might have his students draw the north and east vectors as close to scale as they were able and then complete the rectangle and diagonal. Then measure the length of the diagonal to get “resultant velocity” and with a protractor, measure the angle from north. It would not be as accurate, but it would save explaining tangents and the terminology “arctangent” and the Pythagorean theorem.

These were the questions asked in Part 5 with some answers:

Should the North American plate be considered "rigid"?

No, it flexes to bend under another plate in subduction, and can rise under the pressure of volcano building.

Which portions of the plate would you expect to be experiencing the most intense deformation and regional metamorphism?

Subductions (where the Jaun de Fuca bends under the North American plate, and hotspots of volcano building, as in the Cascade mountains of Washington state.

Is there a relationship between the magnitude of the velocity vectors and their geographic locations (coastal, urban corridor, or Eastern)?

Coastal vectors have magnitudes bigger than the hotspot vector areas and volcano building.

What possible outcomes can you imagine if different portions of the plate continue moving at different rates over a million years?

Portions of land could break apart or mountains form where volcanos erupt. There would be large magnitude earthquakes when pressure builds to cause slipping between the plates

Here are some drawings of the plates in the Western U.S. and their directions. If you use the Google “images” search engine, you would find these.

[pic][pic][pic]

Here is a public map I made on google map with a SEAT vector and a PABH vector.

Go to maps. and search for “PABH SEAT compare” or “SEAT direction, position 2004-2008” Let me know if you do not get it on Google Maps. I can make you a collaborator and google will send you the link directly.

The vectors I made do not have arrowheads, and the SEAT ended up with a vector a little away from the actual SEAT station. Its hard to get the vector exactly where you want it, but kids will be better at this than you are. So try Part 5.

Shelly Olds, on eof the chapter authors, has told me that you can “check” your vector length and direction by going to the Unavco site data for Educators (there is a link in the Part 1 step-by-step), and then to a station and then to a link labeled PBO Station Home Page.

From there look for Data products tab along the top. Then choose Statistics (detrended). The north and east velocities are graphed and annual velocities are printed for each there.

I am attaching to your email my graph of the PABH station line fits. It is an excel file.

Regards,

Rita Freuder

rita.freuder@

................
................

In order to avoid copyright disputes, this page is only a partial summary.

Google Online Preview   Download