SO461 Geological Oceanography

Fall 2008 Test 1--A version

 

Diagrams

4 @ 20 points

80

 

Short answer

4 @ 5 points

20

 

Total

 

100

 

 

Authorized reference:

  1. This test will be open book. Students can use their own copy of the textbook, with any notes they have permanently written in it. No papers can be attached to the text, and class notes and handouts will not be allowed. Books will not be shared during 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.

 

Diagrams: These 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. You must answer four of the five questions.

 

Short Answer: The questions should be answered with several sentences (no more than a short paragraph). You must answer four of the five questions.

 

Budget your time. If you try to look up everything in the text book, you will run out of time. Do not leave anything blank, and note that I am looking for an understanding of the important concepts and appropriate use to terminology. An answer that does this will get more credit than finding and copying a sentence in the book that includes the word asked for.

 

All work on this exam is individual. You may not any materials (books, notes, computers), and you may not use IM, texting, talking, or any other means to communicate with other individuals.

 


 


 

Figure 1. The three magnetic anomaly profiles on the previous were acquired in the same region, and all have the same horizontal scales (in km) and vertical scales (in nannoteslas). The time diagram on the bottom shows the durations of normal and reversed periods during the last 20 Ma, and its horizontal scale does not correspond with any of the profiles above.   [B version had a different diagram, given below]

 

(3) What are these magnetic profiles actually measuring?

 

(8) Label at least five anomalies on each profile with your estimate of the age in millions of years, and show where they occur on the time line at the bottom.

 

(3) On each profile, mark the location or the ridge or indicate the direction in which you would look to find the ridge that created this seafloor.

 

(3) How does the spreading rate vary for each profile? For one profile, show how you would calculate it, and then indicate whether the other two would have faster or slower spreading rates.

 

(3) How do these profiles relate to the Euler pole for the two plates involved?



Figure 2. The diagram on the previous page shows a sequence of rocks that you found while walking through the scenic mountains of Oman on your graduation leave. The thickness scale is in meters. Discuss what you can infer about the geologic history from these rocks. For full credit you should have something to say about each rock layer, and a brief summary/conclusion.

 


 

 

Figure 3. The diagram above shows the focal mechanisms for selected earthquakes in a region that is about 700 km across.    [B version had a different diagram, given below]

 

Pick two representative and distinctly different earthquakes that will do the best job of explaining what is happening, and show the likely orientation of the fault plane and the type of fault involved. Be specific and include numbers; list and defend any assumptions you make.

 

On the diagram, sketch a possible plate boundary or boundaries and indicate the plate motions suggested by the earthquake data.

.


 

Figure 4. Sketch a continental margin, showing characteristics of the continental and oceanic crust. How does the concept of isostasy relate to the diagram?


 


 


Figure 5. The map on the previous page shows a region, the location of an earthquake with its associated focal mechanisms, and a topographic profile through the epicenter of the earthquake.

 

  

         What kind of fault failed during this earthquake, and what is its orientation? 

 

         Why did the topographic profile run in the direction it does? Would there be a better direction in which to orient it?

 

  

         Do you see anything in the topography which matches the orientation of the fault plane?

 


 

 

Short Answer: Briefly discuss 4 of the following 5 terms. Your answer must explain what the term means, and you must use one of the figures from the first part of the exam in your explanation. Clearly refer to the figure you are referring to.

          Figure ____ Uniformitariamism:

         Figure ____ Moho:

         Figure ____ Magnitude:   Richter, and different from Mercalli Intensity

         Figure ____ Limestone:

         Figure ____ Graben:


 

 

SO461 Geological Oceanography

Fall 2008 Test 1--B version Significant Differences

 



 

 


 

Figure 1. The three magnetic anomaly profiles on the previous were acquired in the same region, and all have the same horizontal scales (in km) and vertical scales (in nannoteslas). The time diagram on the bottom shows the durations of normal and reversed periods during the last 20 Ma, and its horizontal scale does not correspond with any of the profiles above.



Figure 3. The diagram above shows the focal mechanisms for selected earthquakes in a region that is about 700 km across.

 


 

Figure 1. Answers.

 


Figure 3 Answers

 


Figure 5 Supplemental Information


SO461 Geological Oceanography

Fall 2008 Test 1--Makeup Exam Differences

 

 

Figure 1.  The three magnetic anomaly profiles on the previous were acquired in the same region, and all have the same horizontal scales (in km) and vertical scales (in nannoteslas).  The time diagram on the bottom shows the durations of normal and reversed periods during the last 20 Ma, and its horizontal scale does not correspond with any of the profiles above.

 

What did the magnetometer used to create these profiles actually record?

 

Label at least five anomalies on each profile with your estimate of the age in millions of years, and show where they occur on the time line at the bottom. Insure that you label an anomaly near the edges of each profile.

 

On each profile, mark the location or the ridge or indicate the direction in which you would look to find the ridge that created this seafloor.

 

How does the spreading rate vary for each profile?  For one profile, show how you would calculate it, and then indicate whether the other two would have faster or slower spreading rates.

 

Sketch a possible set of plate boundaries that could create this pattern of anomalies.

 

 

Short Answer:  Briefly discuss 4 of the following 5 terms.  Your answer must explain what the term means, and you must use one of the figures from the first part of the exam in your explanation.  Clearly refer to the figure you are referring to.

 

         Figure ____Superposition:

         Figure ____  Moho:

         Figure ____Chemical sedimentary rock:

         Figure ____  Graben: