SO461 Geological Oceanography

Fall 2015 Test 2





3 @ 5points




7 @ 10 or 15 points








There are 8 questions, each of which refers to a figure. Four are worth 15 points, and 4 are worth 10 points.   Your answers should clearly indicate understanding of the procedures and concepts involved, and should be well thought out with appropriate terms and details to support your answer. 


Authorized reference:

  1. You may use one 3”x 5” card, personally hand written on both sides, during the exam.  You will turn it in with the exam.
  2. Calculators will not be allowed.  For the calculations, you may set it up and leave the answer in terms of a sum, product, or quotient, or you can make reason simplifications to get a rough idea of the answer.


Budget your time.   Do not leave anything blank, and note that I am looking for an understanding of the important concepts and appropriate use of terminology.


Do not talk about the exam to any students in the course who have not completed the exam.  .


All work on this exam is individual.  You may not any materials (books, notes, computers) other than your personal3”x5” note cared, and you may not use IM, texting, talking, or any other means to communicate with other individuals.  If you are caught with an electronic device that is not turned off and inaccessible you will get a 0 on the exam.



Definitions: define three of these terms with 2-3 sentences, indicating the importance for geology.







(10 points)   The diagram above shows a profile across a plate boundary.  The diagram to the left shows the distribution of earthquakes at the plate boundary.


What type of boundary do you this this is, and why?  Label several features associated with the boundary.

What do the earthquakes tell you about the boundary?


Answer below.  The term Benioff zone would be appropriate to include.  Very few places have quakes 600 km deep.  The depth axis is in km. 

(10 points) Figure 2.  Eltanin 19 profile.



What exactly is depicted on this graph?



How exactly is it measured and computed?



What physical process creates the features that we measure?


(10 points) Figure 3.  Earthquake focal mechanism.



What is actually measured to create this diagram?







What can this diagram tell you about the orientation of the fault that caused the earthquake?  Be very specific.






What kind of fault is this?  Can you predict which way it will move? Draw a diagram showing the force distribution responsible for the fault, and clearly indicate the orientation of the diagram.



(15 points) Figure 4.  Vectors showing the motion of Plate A if Plate B is held constant.


What defines an Euler pole, and why is it important for plate tectonics?



What can you say about the Euler pole for this pair of plates?



What kind of plate boundary boundary is this?  Why?


Could the two earthquake focal mechanism on the diagram go with the boundary?  Name the type of fault for each earthquake, the possible orientations of the fault plane, and where on the boundary you think it could go, and why (or why not if there is no way this kind of fault should be happening here).





(15 points)  Figure 5 .  Map (left) and velocity diagram for three plates (P1, P2, and P3).


If  the P1-P2 boundary is a trench,  plate P1 subducts.

If  the P3-P2 boundary is a trench,  plate P2 subducts.

If  the P3-P1 boundary is a trench,  plate P3 subducts.


Determine the type of triple junction, its stablity, and how it will migrate with respect to the three plates.


Answer below.


(15 points) Figure 7.  Four magnetic profiles measured in the same region.  Scales show distance, age, and anomaly names.


Identify at least three anomalies on each profile, using either the name or the age.  If there is not a ridge on aprofile, indicate in which direction it would be.


Why don’t the anomalies line up vertically on the page?  Include at least two reasons.


How would you compute half spreading rates?  Show how you would compute on one profile (you do not need very accurate numbers), and indicate which of these profiles would have the fastest and slowest spreading rates.


Answer below.

(10 points) Figure 8.  Seismogram recorded in Krrgyzstan.  The earthquake was in Afghanistan




How is a seisimogram like the one above converted into a number to record the size of the earthquake, and what scale is used?




Does distance from the epicenter affect the record at this station, and  does that affect the size of the earthquake on the scale you just discussed?



There is a second scale used for earthquakes.  What is it, and how does it differ from the first one, both in how it is computed and values obtained for each earthquake?








Spreading rates, top to bottom: 29.9, 39.9. 49.2, and 57.3 mm/yr.