2.8 pg 2
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CUNY Hunter College *
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10100
Subject
Geology
Date
Apr 3, 2024
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1
Uploaded by DukeHeron2797
B Notice line B-B' on the map in part A and the fact that shallow, intermediate, and deep earthquakes occur along it. [Each earth- quake begins at a point beneath the surface called the focus (plural, foci).] Using data that were provided by the U.S. Geological Survey in Fig. A2.8.2, plot the locations of earthquake foci on the cross-section (Fig. A2.8.3). Volcanoes also occur at Earth’s surface along line B-B', and their positions are indicated along the ground-surface profile near the zero-depth line. Location East Depth of Location East Depth of Location East Depth of or West of Earthquake (or or West of Earthquake (or or West of Earthquake (or Trench volcano location) Trench volcano location) Trench volcano location) 200 km West 20 km 260 km East 120 km 450 km East 150 km 160 km West 25 km 300 km East 110 km 500 km East 30 km 60 km West 10 km 330 km East 40 km 500 km East 160 km 30 km West 25 km 330 km East 120 km 500 km East 180 km D anch) 2o 390 km East 40 km 590 km East 20 km SRS sl 390 km East 140 k 710 km East 30 k 80 km East 70 km Ao ) i, o 100 km East 10 km 410 km East 25 km 780 km East 530 km 120 km East 80 km 410 km East 110 km 800 km East 560 km 200 km East 110 km 410 km East 150 km 820 km East 610 km 220 km East 30 km 450 km East 50 km 880 km East 620 km Figure A2.8.2 a B West Distance East or West of Trench (km) East B’ 200 100 Trench 100 2(_)0 300 400 500 600 700 800 900 (m—volcanoes (height exaggerated) | e T b TP Depth of Earthquake (km) Text 700 Figure A2.8.3 a 1. What kind of plate boundary is shown in your cross-section? convergent subduction boundary 2. Draw a curve in the cross-section to show your interpretation of where the top surface of the subducting plate is located. 3. Label the part of your cross-section that probably represents earthquakes in the subducting slab. Then label the part of your cross-section that probably represents earthquakes in the South American Plate above the subducting Nazca Plate. 4. At what depth does magma probably originate below the volcanoes, just above the subducting plate.200 to 300 km. How canyoutellyoy can visualize it where the plates start to move. it only makes sense that it would start in the middle depth of the earthquake, where the subducting starts 5. REFLECT & DISCUSS What is the deepest earthquake plotted on your cross-section? Why do you think that earth- quakes occur at hundreds of kilometers depth along subducting slabs but not elsewhere in the mantle at that same depth? The deepest earthquake is 120 feet , The earthquake happens along subducting slabs because one tectonic plate is forced under the other. The dense plate and the less dense plate collide.
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