EES_1030_Activity_1.2.2_2021 (3)
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EES 1030 Oceanography – Homework
Activity 1.2.2: Using Excel to Visualize & Interpret Earthquake Data
Motivating Question: How does the seismic activity at convergent boundaries compare with seismic activity at divergent boundaries?
Data Visualization
Visualizing data helps to reveal patterns and relationships that might not be obvious from simply reading through the raw data itself. At the same time, poorly constructed
or intentionally misleading visualizations can mask these relationships or even lead the reader to draw false conclusions from the data. For these reasons it is important to construct visualizations carefully, choosing the appropriate graph type and being mindful not to obscure or distort data.
Learning Objectives
• Develop proficiency with basic Excel tools
• Compare two different tectonic environments using descriptive statistics of earthquake data
• Quantify attributes and visualize earthquake data in order to evaluate whether data supports a proposed evidence-based conclusion
Task 1: Download Earthquake Data
1. Go to the USGS earthquake archive: http://earthquake.usgs.gov/earthquakes/search/
Tip: These instructions were tested on
Google Chrome, if you use a different
browser you might need to modify
some steps.
2. Click on the orange box on the right-
hand side entitled ‘Draw Rectangle on
Map.’ Once the map window opens,
zoom in a bit to focus on the south
Pacific ocean near New Zealand.
3. Then click and drag to create a
rectangle around the convergent
boundary at the Tonga/Kermadec
Trench
. (see example to the right)
4. Record the coordinates of your
rectangle, which are shown in the lower
Deliverables (marked with an arrow)
Once finished the following tasks, upload a .pdf document to Brightspace with your answers:
Answers to Questions 1–3
Graph from Task 3
Google Earth screenshot
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right corner (see example). You will need the coordinates for all four cardinal directions (N, S, E, W). Note the coordinates are given in decimal degree. You will need this information later.
5. Click ‘Use this Region’ to proceed.
6. Under ‘Date & Time,’ change the date and time parameters for the search to be from 2010-01-01 0:00 to 2015-12-31 23:59.
7. Increase the minimum magnitude to 4. Leave the maximum magnitude blank.
8. At the bottom of the page, select ‘CSV’ for the output format. (CSV = comma-
separated values)
9. Limit the number of data by entering 500 under ‘Number of Events’
10. Click ‘Search.’ Save your CSV file with a useful name.
11. Without altering any other options, change the output format to ‘KML’ (read by
Google Earth)
12. Under the ‘KML-Specific Options’ select ‘Color by Depth’ instead of ‘Color by Age.’ Be sure to leave ‘Animated’ unselected. (This might be a feature you want
to explore in the future.)
13. Click ‘Search’ again. Save your KML file with a useful name.
14. Now
repeat all of these steps to obtain the data for a divergent plate boundary, along one of the mid ocean ridges
. These are little hard to recognize in the map, but the Mid Atlantic Ridge is a good example to use. Try to make your search area roughly the same size as first one. CHECK: At this point, you should have 2 CSV files and 2 KML files -- one each
for a convergent boundary and a divergent plate boundary.
Task 2: Descriptive Statistics
Now you have downloaded two CSV files of your earthquake data for the regions you selected. Keep in mind that a comma separated values (CSV) file differs from an Excel
(xls) file in the sense that CSV is much simpler format than an Excel file. Most versions of Excel are well suited to reading CSV files and you may not even notice a difference. However, after opening your CSV file in Excel you should ‘Save As’ and select ‘Excel Workbook’ so that you do not lose any of the functionality required for analyzing and visualizing the data properly.
Just looking at the raw data you probably cannot draw meaningful comparisons between convergent and divergent boundary earthquakes. However we can use ‘descriptive statistics’ such as mean, median and standard deviation to begin to see if
earthquake magnitudes and depths differ between convergent and divergent boundaries. There are many different types of descriptive statistics and multiple ways
to calculate these statistics in Excel. A very simple guide can be found here:
https://www.edupristine.com/blog/statistical-functions-in-excel
Consult Homework 1.2.1 Supplement for additional background & detailed Excel tips and tricks.
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Question 1: What are the descriptive statistics (see chart below) for the depth and magnitude of the earthquakes both environments? Tip: Because the number of rows is large (500) it will be easier to specify the data range manually (e.g. by typing ‘D2:D501’) rather than trying to click and drag your data selection. (ctrl+shift+arrow key can also be a helpful keyboard shortcut in excel for selecting large amounts of data in situations like these)
The table below will help you organize your calculations. Convergent Boundary
Divergent Boundary
Depth
Magnitude
Depth
Magnitude
Maximum
Minimum
Mean
Median
Std. Dev.
Question
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: How do the basic descriptive statistics of the two datasets compare? How would you explain these differences with respect to the tectonic process operating at each location?
Task 3: Visualize the data using Excel
Now it’s time to put your data to work by representing them graphically. We will be using an X-Y scatter plot to view the data from the convergent margin.
Task 3.1. Create an X-Y marked scatter plot of the relationship between earthquake longitude and depth.
1.
Open your convergent boundary
earthquake workbook.
2.
Select the depth and longitude columns.
Hint
: You can select entire columns by clicking on the column index letter. To select adjacent columns just click and drag across the column indices you wish to select. You can also hold ‘shift’ and click adjacent columns to select multiple columns. ★ Pro-tip
: To select multiple non
-adjacent columns, hold the ‘control’ (PC) or ‘command’ (Mac) keys while you click.
3.
Using the ‘Insert>Chart’ dropdown menu (see yellow oval below) or the ‘Insert’ tab (red oval below), find the X-Y scatterplot option. A chart should then appear
on your spreadsheet.
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ALL CHARTS SHOULD HAVE A TITLE AND AXIS LABELS
. Without this basic
information, a graph is essentially useless. 4. Format your chart to allow readers to better understand it:
a.
Change the title to something more informative e.g. (Earthquake Depth vs. Longitude - Convergent Boundary)
b.
Add axis titles (‘Longitude’ on x axis, ‘Depth’ on y axis), see link for instructions: http://goo.gl/ZhqFF3
★ Pro-tips
: A couple of other formatting changes would greatly improve the appearance of this plot:
Excel will often default to having the axis start at zero. In this case however,
to see the detail and structure of the longitude data, we should reduce the x-axis range to avoid compressed data and excess white space
.
Reversing the vertical y-axis would also be logical in this case, as the axis depicts depth below the Earth’s surface.
If you would like to experiment with these changes the following link will get
you started: http://goo.gl/eKoda2
Save both plots, and then copy and paste them into your word processor to submit as part of your assignment.
Task 4: Visualize the data using Google Earth
1.
Open the KML for the convergent boundary you saved earlier (you may have to
find it in your Download folder first). The file should automatically open in Google Earth with a double-click, or if not, you can open the file within Google Earth by going to the “Open file” in the menu. (NOTE: when you open the KML file, Google Earth will sometimes zoom to the continental U.S. instead of your earthquake data – in this case, just navigate to the area you selected for your data and zoom in a bit, and then all of the data should appear.)
Now you can see where these earthquakes lie on the globe. For some earthquakes you can also click on the data point to open a small tab with more information about that particular event. 2.
Do the same for your divergent boundary KML.
For each boundary, save an image from Google Earth and include it in your submission.
Question 3: What conclusions can you draw from your visualizations of these data? Hint: Think about the difference in the depth of earthquakes between the two environments and about what kind of tectonic activity is
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happening within and between both regions. You can also refer to your descriptive
statistics as well, and as always: Don’t forget units!
Explore Deeper (optional):
Download earthquake data for another plate boundary in the world. Based on your analysis above make some predictions about how you would expect earthquakes to be distributed on this boundary. Check your predictions with the descriptive statistics and visualizations of your new dataset following the steps above.