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Embed code for: Geology fall 2016 Lesson 1
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G341U Homework 1: Fun with Plate Tectonics and Google Earth
In this homework you will learn about the relationship between plate boundaries, distribution of earthquakes and volcanoes, and bathymetry/topography.
IMPORTANT………….READ THIS first: This exercise uses Google Earth (http://www.google.com/earth/index.html ) and Google Earth overlays (.kmz files created by various members of the scientific community) and information from the USGS website including seismic data and maps. To import these files into Google Earth, simply pick them up with the cursor and drop them into Google Earth. You can activate/deactivate the individual layers in the “Temporary Places” folder located on the panel on the left.
Part 1a: The Atlantic Ocean: Tectonics, Earthquakes, Bathymetry
Question 1: First, drop the “Earthquakes 1986-2005.kmz” file into Google earth. This layer shows the locations of actual earthquakes with magnitude >6 that have occurred from 1986 to 2005, and their relative depths (in km). If you click on an individual earthquake data point, you will see the exact year, magnitude, and depth (km) of the earthquake. Also, drop “Earths_Tectonic_Plates.kmz” into Google Earth. This shows the location and nature of the plate boundaries.
(a)Where is the plate boundary located that separates the South American and African Plates? (b) What type of plate boundary is this? The Mid-Atlantic Ridge—Oceanic plate (rift valley)
Question 2: (a) Along what feature do the earthquakes in the Atlantic Ocean occur? (b) And, are they relatively shallow or deep? (a) The Mid-Ocean Ridge----(b) They are deep
Question 3: Now, drop “seafloor_age_10my_isochrons.kmz” into Google Earth. This may take a minute to load so please be patient. This layer shows the age of the ocean floor, by color. a) What is the approximate age of the crust at the plate boundary? (b) Describe how the sea floor age changes as you go from the Mid Atlantic Ridge plate boundary toward the east coast of South America.
9.6 Million years (b) The age of the sea floor increases incrementally from the ridge towards the east coast of South America.
Question 4: Drop “SRTM30_PLUS.kmz” into Google Earth. (This also may take a minute to load.) This is a file showing the topography of the earth, but more importantly for us, it shows the bathymetry of the oceans. (FYI: “)” refers to the depth of lakes and ocean floors. It is the underwater equivalent of “Topography”.) In the oceans, darker colors represent deeper waters, and lighter colors represent shallower waters. a) First, look up what SRTM30 means. VERY briefly and generally, how was this data acquired? (a) SRTM30 is a near-global digital elevation model (DEM) comprising a combination of
data from the Shuttle Radar Topography Mission and the U.S. Geological Survey's GTOPO30 data set. It can be either an SRTM data set enhanced with GTOPO30, or as an upgrade to GTOPO30.
Toggle back and forth between the “seafloor_age” layer and the “SRTM30” layer (again, activate/deactivate the layers by clicking on the checkbox next to the layer in the “Temporary Places” heading on the panel on the left) b) Describe the relationship between sea floor age, bathymetry, and the mid-Atlantic plate boundary. (b) The sea floor age increases in number as it moves away from the plate boundary and has magnetic and reverse magnetic fields that alternate from one to the other. The mid-Atlantic boundary is considered a divergent plate boundary due to the land moving away from one another.
Question 5: Is crust being created or destroyed at the Mid Atlantic Ridge plate boundary? The crust is being created and destroyed.
Part 2a: New Zealand/Tonga: Tectonics, Earthquakes, Bathymetry
Question 6: Deactivate the “seafloor_age” layer now. With the “SRTM30” layer activated, locate the island of Tonga (if you don’t know where this is, type “Tonga” into the search bar. Google Earth will take you there.) READ THIS: Make sure you have a distance scale at the bottom left. If you don’t, go to “VIEW” at the top of the screen, and click “Scale Legend” and it should appear. You’ll want kilometers instead of miles, so again at the top, click on “Google Earth” > ”Preferences” and then find “Units of Measurement” and select “meters, kilometers”.
Ok, Tonga is an island that sits near a convergent a plate boundary (disregard the divergent plate boundary labeled here-the red line). Make sure you are properly zoomed out (field of view of the screen at ~1500km or so).
Briefly describe in words how the ocean depth changes as you approach and cross the Tonga plate boundary from ~500 km east of Tonga to ~250 km west. Remember, dark=deeper, ligher=shallow. It might also be useful to look only at Google Earth’s bathymetry, where different shades of blue indicate a depth (to do this, deactivate the SRTM30 layer). The ocean depth is deeper on the east side of the trench and becomes more shallow moving to the west position of the plate.
Question 7: Activate the “Earthquake” layer. Compare the distribution and depths of earthquakes shown for the mid-Atlantic plate boundary (see question 1) and the Tonga-Kermadec plate boundary shown. The mid-Atlantic plate boundary has earthquakes that have a linear line form. The line of earthquakes stretch all along the plate boundary and are minimal in number. The Tonga-Kermadec plate boundary has a more concentrate activity of earthquakes and the area of earthquakes in this plate boundary is much smaller than the area(linear) in the mid-Atlantic plate boundary. The depths of the earthquakes are similar in km’s with the Tonga-Kermadec plate boundary having more quakes at a lower depth.
Question 8: (a) Describe the distribution of earthquakes as you go from east to west. (b) H=ow might you interpret the distribution and depths of earthquakes at these locations at the Tonga plate boundary? (hint: see the Week 1 Lecture 2 slides) (a) The distribution of earthquakes increases in number as you go from east to west and earthquakes progress from shallow to deep. (b) The Pacific Plate and the Australian Plate exhibit large amounts of earthquakes in the shallow depths and earthquakes dwindle in number as the subduction plate goes deeper to a point where the number of earthquakes increases in number at the lower and lowest depth of the subduction plate.
Question 9: Note where the shallowest earthquakes are located along the Tonga plate boundary. What is this subduction zone feature called? It is the Kermadec-Tonga subduction zone and is a convergent plate boundary. The Tonga trench is located in this subduction zone and its deepest point is called the Horizon Deep.
Question 10: Drop “Active Volcanoes.kmz” into Google Earth. What is the depth range of earthquakes (in km) that are spatially related to the active volcanoes along this Tonga plate boundary? (you may have to deactivate the “Tectonic Plates” layer to read the legend for the earthquake layer as they overlap, annoyingly.) The Oceanic Lithosphere has earthquakes that range from 5 km to 100 km, 100 km to 400 km, and from 400 km to 700 km deep. The depths afore mentioned are depth measurements from sea level/and or the volcano level.
Question 11: Now, fly across the ocean to the central Andes in western South America (Peru, Chile). (a) Is the relationship between earthquake depth and active volcanoes similar here? (b) How about in Central America (Guatemala, El Salvador, Nicaragua, etc.)? (a) The earthquake depth in western South America is much more shallow than the Tonga plate boundary. The depth in the western South America only reaches 160 km’s. (b) The depth of earthquakes and volcanoes becomes more shallow than the western region of South America.
Question 12: Generally, the Pacific Rim (where land encircles the Pacific Ocean) is often called the “Ring of Fire”. (a) What is the dominant type of plate boundary along the Ring of Fire? (b) Is crust being created or destroyed at this plate boundary? (c) Does this type of boundary continue, un-interrupted around the Ring of Fire? (d) Are there active volcanoes in an uninterrupted line along the entirety of the Ring of Fire? (a) The dominant type of plates are ocean-continent convergent boundaries and ocean-ocean convergent boundaries. (b) The crust on the subduction plate will be destroyed and its crust is forced back into the earth’s interior. (c) No (d) Yes, that is why they call it the Ring of Fire.he screen at ~1500km or so).
Question 12: Generally, the Pacific Rim (where land encircles the Pacific Ocean) is often called the “Ring of Fire”. (a) What is the dominant type of plate boundary along the Ring of Fire? (