Title: CU2M2 Lab Part 2 Answer Key
Course: SkillsCom GS 106 14.0 > Section: Credit Unit 2 Module 2

10) Looking at the first map, which shows the seismicity from 1990 to 2011, orange are up to 35 km depth, yellow are up to 70 km depth, green are up to 150 km depth, and lastly, blue are up to 300 km depth. What do you notice about the depth pattern of the earthquakes as you move west across the island? How do you account for that pattern? (Credit: U.S. Geological Survey, Department of the Interior/USGS)

Picture: http://neic.usgs.gov/neis/eq_depot/2011/eq_110311_c0001xgp/neic_c0001xgp_s.jpg

Alt Text: Map showing the different depths of earthquakes over Honshu Island, Japan.

Answer: While looking at the earthquakes and their corresponding depth we can see that as one moves west across the island the earthquakes start shallow and they get progressively deeper. The deepest earthquakes seem to be the farthest west on the island. We can account for this pattern through subduction. As the Pacific plate subducts underneath Japan the plate begins to curve as it plunges into the mantle. So, shallow earthquakes are found where the subduction zone begins but deepen as the plate deepens into the mantle as we move west.

Question CU 2 M2 #10 | Student correctly identifies and describes the pattern of earthquakes seen 4 pts | Student correctly identifies and describes the pattern of earthquakes seen but misses several key concepts 3 pts | Student correctly identifies the pattern of earthquakes seen but incorrectly describes why that pattern occurs 2 pts | Student correctly identifies the pattern of earthquakes seen but does not describe why that pattern occurs 1 pt | Insufficient 0 pt

11) Now look over this map that shows the highest magnitude earthquakes, greater than M7, over the past 111 years. At what depth are these earthquakes located (orange are up to 35 km depth, yellow are up to 70 km depth, green are up to 150 km depth, and lastly, blue are up to 300 km depth)? Where are the earthquakes located in relation to the island of Honshu, Japan? How can you account for the earthquakes depth?

Picture: http://neic.usgs.gov/neis/eq_depot/2011/eq_110311_c0001xgp/neic_c0001xgp_7.jpg

Alt Text: Map showing all M7 earthquakes or greater since 1900 over Honshu Island, Japan.

Answer: The depth of most of these earthquakes are quite shallow, up to 35 km depth some are a bit deeper up to 70 km. The are also located just offshore of Honshu, Japan, not actually on the island. The reason these earthquakes are high magnitude and so shallow has to do with the presence of a subduction zone on the coast. Those earthquakes mark the location where the Pacific Plate begins subducting into the mantle. This boundary is very shallow in this location and so the earthquakes that occur on this portion of the boundary are therefore shallow as well.

Question CU 2 M2 #11 | Student correctly identifies the depths and location of the earthquakes and correctly reasons why the earthquakes occur at these depths 4 pts | Student correctly identifies the depths and location of the earthquakes and correctly reasons why the earthquakes occur at these depths though misses several key concepts 3 pts | Student correctly identifies the depths and location of the earthquakes but does not explain reasons why the earthquakes occur at these depths 2 pts | Student correctly identifies either the depths or location of the earthquakes but does not explain reasons why the earthquakes occur at these depths 1 pt | Insufficient 0 pt

12) Watch the video at http://www.youtube.com/watch?v=-k6WqS0Ov4U. How many miles of coastland did the reporter say was inundated by tsunami waters? How tall did they say the wall of water was? How far did this surge of water move inland?

Answer: 1300 miles of coastland was inundated by the tsunami, in places the tsunami wave was 3 stories tall, and the wave travelled 6 miles inland.13) Watch the movie posted as the hyperlink at the top of the page. What happens as a plate subducts underneath another plate to cause the tsunami seen in Japan?  Based on the shape of a tsunami wave, why are areas across oceans, thousands of miles from the origin of an earthquake, still at risk of being affected by the wave?

Question CU 2 M2 #12 | Student correctly reports each dimension of the Japan tsunami 4 pts | Student correctly reports 2 out of the three dimensions of the tsunami 3 pts | Student correctly reports 1 out of the three dimensions of the tsunami 2 pts | Student incorrectly reports the dimensions of the tsunami but attempts question. 1 pt | Insufficient 0 pt

13) Watch the movie posted as the hyperlink at the top of the page. What happens as a plate subducts underneath another plate to cause the tsunami seen in Japan?  Based on the shape of a tsunami wave, why are areas across oceans, thousands of miles from the origin of an earthquake, still at risk of being affected by the wave?

Mov: http://ffden-2.phys.uaf.edu/645fall2003_web.dir/elena_suleimani/generation_small.mov

(If that doesn’t work in Canvas here is a picture)

Picture: http://pubs.usgs.gov/fs/fs150-00/images/cross_section.jpg

Picture: http://factsanddetails.com/media/2/20110413-USGS%20Tsunami%20fig07.jpg

Alt Text: The formation and movement of a tsunami wave during a megathrust earthquake.

Answer: As the plate subducts, the overlying plate is pushed backwards accumulating a lot of stress. When the overlying plate snaps back to its original position the elevation of the ocean floor changes causing a large ripple in the ocean. That ripple, or wave, of energy is sent in every direction. The tsunami wave is circular, like ripples in a pond, and areas that are across an ocean from where a tsunami wave is produced can even still see the affects of the wave as it will eventually reach their coast.

Question CU 2 M2 #13 | Student correctly describes what happens as a plate subducts, the shape of the tsunami and why tsunamis can affect entire oceans 4 pts | Student correctly describe what happens as a plate subducts, the shape of the tsunami and why tsunamis can affect entire oceans but misses several key points 3 pts | Student correctly describes what happens as a plate subducts, why tsunamis can affect entire oceans, but does not describe the shape of the tsunami 2 pts | Student correctly describes what happens as a plate subducts but does not describe the shape of a tsunami wave or how it can affect entire oceans 1 pt | Insufficient 0 pt

14) Based on the position of the Jaun de Fuca plate off of the Pacific Northwest Coast and the associated plate boundary, is it likely we could see a similar earthquake and tsunami like that seen in Japan? Do you think something like this has happened in the Pacific Northwest before?

Answer: Absolutely, we have a similar plate boundary on our coast where the Juan de Fuca plate is subduction and we are accumulating stress in the plate boundary during subduction. If the boundary were to slip we would see both a large magnitude earthquake and an associated tsunami. And since this plate boundary has been on our coast for a long time, we have seen an earthquake and tsunami before, in 1700 in fact.

Question CU 2 M2 #14 | Student fully describes the boundary, the past occurrence and future likelihood of an earthquake and tsunami on the Pacific Northwest Coast 4 pts | Student fully describes the boundary, the past occurrence and future likelihood of an earthquake and tsunami on the Pacific Northwest Coast But misses a few key points 3 pts | Student fully describes the boundary and future likelihood of an earthquake and tsunami on the Pacific Northwest Coast but does not discuss past occurrences 2 pts | Student fully describes the boundary but does not describe the past occurrence and future likelihood of an earthquake and tsunami on the Pacific Northwest Coast 1 pt | Insufficient 0 pt