earth science3
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assignment_3_platetect_seismol_fall202.docxPSC 121, Fall 2020 NAME _____________________________
Homework #3, Due Wednesday, September 23rd (30 points)
The material for these questions is Chapter 20.1 all of Chapter 21 and class notes. However, feel free to use any Internet sources to supplement (like for question #4)- but for full credit you need to cite them.
1. Subduction is the process of one lithospheric plate descending beneath another. Why does the oceanic portion of the lithosphere undergo subduction while the continental portion does not? (2 pts)
2. Answer the question posed at the beginning of the class on Sept 14- why do we have long mountain ridges at the bottom of the ocean? (2 pts)
3. What type of plate boundary produced the following mountain ranges? (2 pts)
a. Appalachians
b. Andes
4. On Google Earth, we see a long dark streak extending northeastward from New Zealand. What is this feature and how is it explained by plate tectonics? (2 pts)
PSC 121, Fall 2020 NAME _____________________________
Assignment #3, page 2
5. Calculate the age of the Atlantic Ocean using Google Earth. (10 pts total)
a. Pick 4 locations where the Americas used to touch Africa or Europe when Pangea existed and calculate the current distance (probably best in cm). Use class notes or any Internet resource to reconstruct how the continents aligned with Pangea. Of the 4 locations- pick 2 in the North Atlantic and 2 in the South Atlantic. Make sure to write down the latitudes and longitudes of each end point.
b. The width of the Atlantic grows by about 5 cm year. From the formula distance = rate x time, you can solve for the age of the Atlantic as:
time = distance across Atlantic/speed that plates move away from each other
c. Fill in the table on the next page using your Google Earth measurements and the formula
PSC 121, Fall 2020 NAME _____________________________
Assignment #3, page 3
Table for Age of Seafloor question
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Start lat |
Start long |
End lat |
End long |
Distance |
Derived Age
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d. Give an assessment both as to how well you did and your conclusions about the age of the Atlantic.. Don’t sweat if you don’t match the observations below exactly- it’s your analysis which counts! Your answer should include the following:
i. What are possible errors in your analysis?
ii. Are the ages the same everywhere along the edges of the current Atlantic Ocean?
iii. Which part started separating first?
PSC 121, Fall 2020 NAME _____________________________
Assignment #3, page 4
6. More plate movement. The San Andreas Fault moves about 3.5 cm per year. If you owned property on either side of the Fault in 2000 and built a fence across the fault, how far apart would the two sections of the now-broken fence be now in 2020? (this is essentially question # 37 in Chapter 21). Formula is basically the same as in question #5 above (distance = rate x time) (2 pts)
Seismology – The seismographs which follow on the next page are 2 hypothetical measurements of an earthquake. Use them to answer the following questions
7. What is the S-P intervals and the S wave amplitudes for the earth quake?
Feel free to mark on the graph if you think it helps. (4 points)
8. A reasonable conversion of S-P interval to distance is with the following formula.
epicenter distance (in km) = 7 x the S-P time interval (in seconds) (4 points)
9. Lastly the Virginia Earthquake of 2011 was estimated to be 5.8 on the Richter Scale. If we had had a seismograph at PGCC, which is about 200 km away from the epicenter, what S wave amplitude and what S-P time interval would we have recorded? Compared with the earthquake measurements you analyzed, how much shaking would we have felt here in Largo? More, less, or about the same? (compare with seismographs) (2 pts)
PSC 121, Fall 2020 NAME _____________________________
Assignment #3, page 5
Seismographs
PSC 121, Fall 2020 NAME _____________________________
Assignment #3, page 6
Nomogram
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