GEOL 1033, General Oceanography
REVISED Exercise 9 (Lesson 16)
Question and Answer Sheet:
E9
Name: __________________________
ID #: ____________________
1. Using the data provided on page 107 of the Study Guide, plot on the crosssection on the next page the location of each earthquake focus. (Mark a small
"x" at the correct depth and distance for each data point.)
2. What pattern emerges for the locations of these earthquake foci?
__________________________________________________________________________
3. Estimating carefully by eye, draw a straight (or slightly curved) trend line
through the data points to show this pattern. (Do not connect every data point.)
4. Describe in one sentence the relationship(s) between depth of earthquake foci
and their distance (east or west) from the Tonga Trench? _______________________
__________________________________________________________________________
5. Explain why we might interpret this zone as a fault. ________________________
__________________________________________________________________________
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6.
Considering the position of the trench and the volcanic islands, show the
directions of relative movement along the fault zone by drawing two arrows on
the cross-section, one above the fault zone and one below.
7. Why does a deep trench develop? ___________________________________________
________________________________________________________________________
8. Why do we find a volcanic island arc parallel to and west of the deep trench?
________________________________________________________________________
________________________________________________________________________
9. Briefly explain how this earthquake focus pattern and fault interpretation
supports an aspect of the theory of plate tectonics? __________________________
________________________________________________________________________
________________________________________________________________________
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10. In plate-tectonic terms, what are these fault zones? _____________________
11. At what depth would heated and sinking oceanic lithosphere probably not be
rigid enough to produce earthquakes?
_______________ km
12-13. Locate the Tonga Trench and the Tonga Islands on a world map or globe
that shows seafloor topography. What are the approximate latitude and longitude
of Tonga Island?
12. Latitude ________________
13. Longitude ________________
14. Mark the location of the following deep-sea trenches (refer to textbook) on
the map on the back of this sheet (on page 109 in the Study Guide) with the
capital letters indicated in parentheses after their names:
Tonga Trench (T),
Aleutian Trench (A),
Sunda-Java Trench (SJ),
New Hebrides Trench (NH),
Mariana Trench (M),
Kermadec Trench (K),
Japan-Kuril Trench (JK),
Peru-Chile Trench (PC)
So. Sandwich Trench (SS), Puerto Rico Trench (PR),
Middle America Trench (MA),