1. No category

Name (6 pts):___________________
GSC307: Global Geophysics
Lab 2 (70 pts; 6 for name + staple/paperclip)
Due before start of next Lab 4/23/15
PROBLEM 1 (18 pts)
The pictures below show two (rigid) plates and their boundaries identified as
ridge, trench or transform. Transforms are shown as straight lines with a “T”. Some of
these pairs of plates are impossible, in the sense that there is no velocity field that is
consistent with the boundaries. First try to find a velocity field consistent with all of the
boundaries.
Regarding plate A as fixed, sketch this velocity field over the other plate with
arrows. Oblique subduction and spreading should be considered as possibilities. If you
cannot find a consistent field, mark the diagram “impossible” and show which
directions would be inconsistent. An example solution is shown for 1-2a. Work neatly
and sketch multiple arrows, not just one or two.
PROBLEM 2 (16 pts)
The AB boundary is a transform with right-lateral movement of 3 mm/year. The BC
boundary is a trench along which convergence is occurring obliquely at an angle 45°
east of north.
1. Given the information above, plot plates A, B,
and C in the velocity space diagram. Hold plate
A fixed.
2. Based on your velocity space diagram, draw a
vector on plate C in the cartoon to the right that
shows its velocity relative to plate A.
3. Based on this vector and the plate geometry,
decide whether the boundary between plates A
and C is a ridge, trench or transform. Clearly
write down your answer.
4. Determine AVC. Specify both the velocity in
mm/year as well as its direction. You may
determine these parameters purely graphically
(but work neatly, large errors will not be
accepted!), or by using basic trigonometric relationships.
PROBLEM 3 (30 pts, 10 per diagram)
Make velocity diagrams for the three plate geometries shown on the next page,
following the exact same instructions as in problem 2. (All angles are multiples of 45°.)
Hold plate A fixed.
Include all three plates shown. Determine and write down (clearly!) both the direction
and the magnitude of the relative velocity across the dashed boundary.
Determine and write down whether the dashed boundary is a ridge, transform or
trench.
Note that in these figures, the spreading velocity given is the total spreading velocity
and NOT the half-value.
Make sure to attach your work, if you choose to use your own graph paper.