Lab 2, due before the start of Lab 4/23/15
Transcription
Lab 2, due before the start of Lab 4/23/15
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.