Tracking Tectonic Plates – Cheap Research Essays

Use ruler, protractor and calculator as necessary for the following exercises.

1. The azimuth convention of denoting direction For this convention, “due north is designated as 0°, (and) 90° points to the east, 180° points to the south, 270° points to the west, and 360° points, once again, to the north…If you think of your location as lying at the center of a circle, the direction (azimuth) to any feature can simply be described by its angle of arc in degrees…Azimuth can be measured directly off a map using a protractor, or calculated using simple trigonometric relations.
http://www.dpc.ucar.edu/VoyagerJr/ptbkgd.html
1a. Use Google Earth, Google Maps, consult a road map of the area, or examine the map posted on the door of the lab room. If you traveled along Route 1 from the Penns Neck Circle (intersection with Washington Rd) to I-295, along what azimuth would you be heading? _____________

1b. How about on the way back? _____________
2. While warming up for their famous race, the hare started at point A, hopped 50 meters due north, and then 30 meters due west to end up at point B. The tortoise also started at point A but plodded along a straight line to point B. How far did the tortoise travel and what was his azimuth of travel? Show your work clearly.

3. For the actual race, the tortoise and the hare started together and traveled in the same direction. The tortoise plodded along at 2 cm / sec while the hare hopped at 15 cm/sec. How far apart were they after 1 second? After 10 seconds? At what rate was the distance between them increasing?

Tracking Tectonic Plates
lab handout
The theory of plate tectonic posits that the earth’s lithospheric plates are moving. How do we know plates are moving, how can we track their positions in the past, and how can we predict their positions in the future? For this lab, you will be assigned a particular plate boundary to investigate and will track it through time using two independent methods.
For Part A of this lab, you will investigate your plate boundary using methods which give long term average rates of plate movement over millions of years. You will first apply these methods to a class example, and then to your own plate boundary.
For Part B, you will be investigate your plate using high-precision GPS measurements taken over the last decade or so. You will first apply these methods to a class example, and then to your own plate boundary.
You will prepare a written report (guidelines later on in the lab handout) for submission to your la instructor.

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Part A. Tracking plates by measuring long-term average motions over millions of years

Reconstructions of the earth’s tectonic plate locations through time are available at, among others:
http://emvc.geol.ucsb.edu/downloads.php
http://www.scotese.com/newpage13.htm
http://www.ucmp.berkeley.edu/geology/tectonics.html

On what are these reconstructions and animations based?

1. Following your lab instructors instructions, complete and/or review these exercises which demonstrate how plate motions can be traced over many millions of years. The exercises include:
o Investigating rates of sea-floor spreading at spreading ridges
o The Hawaiian- Emperor Volcanic Chain

2. There are many other examples of how geologic data can be used to determine long-term average rates of plate motions.
Using this data, geologists have developed the global models which generally assume that plate interiors are stable and all of the motion occurs along infinitesimally thin plate boundaries. There are a number of “plate Motion Calculators” that give access to a number of these models in order to calculate the relative and absolute plate motion direction and speed at any point on the earth. We will use one developed by K. Tamaki and K. Okino of Tokyo University:
http://ofgs.ori.u-tokyo.ac.jp/~okino/platecalc_new.html

2a. Start working on the class example by going to the attached spreadsheet and listing the latitude and longitude of each station. There are two ways to do this with Google Earth:
o (Recommended) Right click on each station location, then click on “directions from here” or “directions to here.” A box will open with decimal degrees for latitude and longitude.
? Northern latitudes are positive, southern latitudes are negative.
? Eastern latitudes are positive, western latitudes are negative.
o (Another way) As you move the cursor around, Google Earth gives you the latitude and longitude of the location of the cursor. You could take these values, which are given in deg min sec, and then translate them to decimal degrees.

2b. An abundance of geologic and seismic data indicate that the San Andreas fault is a right-lateral strike-slip fault. On each of the two photos attached to this handout, put two small arrows (about 1 cm in length) on either side of the fault in order to indicate this sense of motion.

2c. On the spreadsheet, indicate the plate (P=Pacific, NA=North American) for each station.

2d. Use the Plate Motion Calculator to determine the long term “NUVEL” model long-term motion for each of the 4 stations and enter the values on the spreadsheet. Use the following parameters:
o From the drop-down Model menu, choose HS3-NUVEL-1A (this gives absolute plate motion, relative to the hotspot frame of reference.)
o For Moving Plate, choose the plate that the station is on (either Pacific or North American).
o For Fixed Plate, choose anything; this is not used in the HS3-NUVEL-1A model.
o Input the latitude and longitude from the spreadsheet.
o On the spreadsheet, record the velocity and azimuth (compass direction) for each station.

2e. On Map A: Long-Term Motion, plot a vector (arrow) that shows the magnitude and direction of long-term plate movement for each station. Use a scale of 20mm/yr = 1 cm.

2f. How are the long-term motions of the North American stations similar to the those of the Pacific stations?
2g. How are the long-term motions of the North American stations different from those of the Pacific stations?
2h. Does this analysis confirm or contradict the observation of right-lateral motion along the San Andreas fault? Explain.

Part B. Tracking plates over the short-term using GPS data

3. The plate motion calculator gives long-term plate motions over millions of years. Another way to track plates is by using the Global Positioning System (GPS), yes, the same system used by increasingly affordable hand-held receivers and included in many new cars. The GPS used for this method is much more precise that the one used by your car, but it works basically in the same way. After reviewing the basics of GPS, your lab instructor will give you the time series plot for one of the stations used for the class example. There is a Blackboard link to the site from which you can get plots for all the GPS stations under Labs/Other files for Lab 4, otherwise type it in manually. Bookmark the site for future reference.
http://sideshow.jpl.nasa.gov/mbh/series.html
Parts of the time series:
• The x- axis is time in decimal years.
• The y-axis is the station’s position resolved into three perpendicular components: latitude (north-south component), longitude (east-west component) and elevation (vertical component).
• Each data “point” is actually a vertical line representing the error of that particular measurement.
• Gaps in times-series data are due to things like snow, power-loss, communication failure, and human or animal vandalism.