Name: ________________________
Due Date: _____________________
Per: ________
40 minutes
Earthquakes & Subduction Zones
Objectives: At the end of this activity you should be able to:
 Use Microsoft Excel to draw a scatter plot, add a best-fit line to plotted data and adjust the scales and axis labels.
 Analyze the plotted data to compare and contrast the behavior of two subducting plates.
Introduction:
Most earthquakes occur at or near plate boundaries. The deepest quakes occur at subduction boundaries. Deep-focus quakes are those with foci deeper than 300 km. Shallow-focus quakes have foci less than 70 km deep.
Intermediate-focus quakes occur in between.
Subducting plate behavior is determined by the age of a plate’s rocks.
Older crust is cooler, and therefore denser, than younger crust. Denser
crust subducts faster and at a steeper angle than less dense curst.
In this activity, you will plot and compare earthquake foci data from two areas where subduction is occurring currently. One of the areas is along the boundary between the Pacific Plate and the Indian-Australian Plate creating the
Tonga Trench. The other area is along the boundary between the Nazca Plate and the South America Plate creating the Peru-Chile Trench.
Procedures:
1.
From the “Novell Applications box”, go to the following folder:
StudentCommon/ Earth Science and open up the Document: EQ Plotting
Data. Print out this document for use later.
2.
From the “Novell Applications box”, open a blank Excel document
3.
Select the Data Table for the Tonga Trench (Data Table 1). Copy and paste that Data Table into “Sheet 1” of a new Excel Workbook. (Paste into Cell A1).
4.
Create the chart: Click the “Insert” tab and then select “Scatter”. Choose
“Scatter with only Markers”. (That should be the first of the scatter charts).
5.
Put your chart into its own tab: Right click on the white area to the right of the chart and select “Move Chart”. Click “New Sheet” and call it “Tonga
Trench”.
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6.
Now add a “best-fit” line to your chart: Under “Chart Tools”, select the
“Layout” tab and choose “Trendline”. Have Excel add a “Linear Trendline”.
(This adds a “best-fit” line to your chart).
7.
Give the chart a title: Under “Chart Tools” click “Layout” and then click “Chart
Title” and select “Above Chart”. A title box should appear. Type “Tonga
Trench” and hit enter. The title will be automatically put into your highlighted textbox.
8.
Add a label for the horizontal (x) axis: In “Chart Tools” click “Layout”, under
“Labels”, select “Axis Titles” and select “Primary Horizontal Axis Title”, choose
“Title Below Axis”. A title box should appear. Change the name of the horizontal (x) axis to “Longitude (w)”.
9.
Add a label for the vertical (y) axis: In “Chart Tools” click “Layout”, under
“Labels”, select “Axis Titles” and select “Primary Vertical Axis Title”, choose
“Rotated Title”. A title box should appear. Change the name of the vertical
(y) axis to “Depth (km)”.
10.
Click the values in the vertical axis so they are selected (a box will appear around them). Right click the depth values so a selection window appears. In this window choose “Format Axis” and make these changes: Click “Values in reverse order” so that 0 is at the top of the vertical (y) axis. For the “Axis
Options” click the button for “fixed” and enter a minimum value of “0” and a maximum value of “700”. Then click “Close”.
11.
Click the values in the horizontal axis so they are selected (a box will appear around them). Right click the longitude values so a selection window appears.
In this window choose “Format Axis”. Click “Values in reverse order” so that longitude values increase to the west.
12.
Repeat the above procedures (Steps 4 - 10) with Data Table 2 (Peru-Chile
Data): Deselect Data Table 1 by clicking off the table. Select Data Table 2.
Paste this data into Sheet 2 in Excel. When naming the chart, call it “Peru-
Chile Trench”.
13.
In the “Format Axis” window, make these changes: Click “Values in reverse order” so that longitude values increase to the west. For the “Axis Options” choose the same minimum and maximum values as you did for the Tonga
Trench. This way, both charts will be drawn with the same vertical axis, making it easier to compare the slopes of their best fit lines.
14.
Fill in Table 1 below using the data in the “EQ Plotting Data” document.
Count the number of shallow, intermediate, and deep earthquakes for each trench. Record in Table 1 below.
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Earthquake Type Focus Depth (km) Tonga Total
Shallow
Intermediate
< 70
70 - 300
Chile Total
Deep > 300
Total number of quakes 41 40
Conclusions:
Use your ESRT pg. 5 to help you answer the following questions about trenches.
1.
Locate the Tonga and Peru-Chile Trenches. Identify the subducting and overriding plates for both locations.
Tonga Trench –
Subducting Plate: ____________________________________________
Overriding Plate: _____________________________________________
Peru-Chile Trench –
Subducting Plate: ____________________________________________
Overriding Plate: _____________________________________________
2.
Locate the East Pacific Ridge. Compare the distances from the ridge to the
Tonga and Chile Trenches. Which trench is further from the ridge?
______________________________________________________________
______________________________________________________________
3.
If the East Pacific Ridge is the source of the subducting crust in both areas, how would the age of the rock at the Tonga Trench compare to the Peru-Chile
Trench?
______________________________________________________________
______________________________________________________________
4.
Now that you know which trench has older rock, what does this say about the temperature of the rock at this trench?
______________________________________________________________
______________________________________________________________
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5.
At which trench is the subducting plate moving westward? _______________
6.
Which plate is subducting at a steeper angle? What does this tell you about which plate has a greater density? Does this make sense based on what you know about the temperature of the rock at each trench?
______________________________________________________________
______________________________________________________________
______________________________________________________________
______________________________________________________________
7.
At the Peru-Chile Trench, the rocks that were once at the surface began subducting 10 million years ago and are now 1000 km from their original position. What is the average rate of subduction in cm/yr? Show Work!
______________________________________________________________
______________________________________________________________
______________________________________________________________
8.
At which trench would you expect the greater rate of subduction? Why?
______________________________________________________________
______________________________________________________________
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