GY305 Global Geophysics: Lab 1
Problem 1: Given the below information, calculate the linear velocity and azimuth of
relative plate motion for point X on the plate boundary between the Pacific and Antarctic
plate:
λP
-64.3̊
φP
96.0̊
λX
-56.7
φX
-140.0
ω
9.1x10-7 deg/yr
R
6371 km
You will solve this problem with an Excel spreadsheet. Print out your solution on a
single sheet of paper, and turn in the spreadsheet on a jump drive.
Problem 2: With the attached tectonic map (Figure 1) of the North American – Juan de
Fuca – Pacific plate triple point, calculate the linear rate and orientation (azimuth) of the
velocity vector of the North American plate relative to the Juan de Fuca plate. Use the
method of vector addition (circuit diagram). This problem should be worked graphically
on a separate sheet of paper with a north arrow for reference. What is the rate of
subduction of the Juan de Fuca ?
1. Velocity of the NA plate relative to the Juan de Fuca plate (cm/yr):____________
2. Azimuth of the velocity vector: ___________________
3. Rate of subduction of Juan de Fuca plate: ________________
Figure 1: Tectonic map of the Pacific - North Am. - Juan De Fuca triple point.
Problem 3: Using the Figure 2 map in your text, measure the latitude and longitude
values of at least six equally spaced points located on the UDINTSEV fracture zone
associated with the east Pacific Rise. Plot these points on a stereographic projection as
a series of points. Convert these points to directional angle values, and best-fit a small
circle geometry through the points. The apical axis point of the fit will be the pole of
rotation between the Antarctic and Pacific plates. Convert the apical point back to
geographic coordinates. Turn in the following materials for this problem:
1. Table of measured geographic coordinates of the fracture zone.
2. Manual plot of geographic coordinates on a stereographic projection (right side = 0̊
longitude)
3. Hard copy of best-fit small circle (use NETPROG program).
4. List both possibilities of the geographic coordinates of the pole of rotation between
the two plates.
Figure 2: Map of East Pacific Rise transforms.
Problem 4: Given the latitude-longitude coordinates of the 4 corners of a hypothetical
tectonic plate, and the lat-long coordinates of the pole of rotation, use an equal-angle
stereographic projection to rotate and plot the new plate corner coordinates after 70
degrees of counter-clockwise rotation (viewed down-plunge) about the pole of rotation:
Corner 1
Latitude
Longitude
40N
49W
Corner 2
40N
30W
Corner 3
10N
50W
Corner 4
10N
20W
Pole
40N
154E
Draw straight lines connecting the original corner points as the starting position of the
plate, and do the same for the rotated corners to show the new position. On the
stereonet make sure that you include tic marks for the cardinal directions, label north
with an “N”, and make a “+” mark at the center of the stereonet. Make the stereonet
radius 3.5 inches.