Earthquakes Everyday: Using GIS to Analyze Global Plate Tectonics
Your Name: _____________________
Summary: In this activity, you will examine global plate tectonics: earthquakes and plate boundaries.
Education Level: University; upper secondary school students could also use this.
GIS Level: Some familiarity with GIS would be helpful.
Time Required: 50 questions; 2 to 3 hours. A subset of questions may be used if less time is available.
GIS Software Used: ArcGIS 10.
Skills :
1) Tabular data joining, sort, query, and analysis.
2) Spatial data sort, query, and analysis.
3) Downloading and formatting data from the Internet for use in GIS.
4) Changing projections.
5) Symbolizing and classifying data.
Goal: To analyze historical and current earthquakes within a GIS, and by extension, to understand how to download and format spatial data from the Internet, map projections, and how to analyze point and polygon data.
Data Management
Create a folder on your computer or on the network where you are storing the data. Make sure this folder has a logical name so that you will understand what its contents are. Do not put any spaces in the folder name. Use underscores if necessary.
You should have the following files corresponding to 6 data layers:
· cntry95.dbf cntry95.sbn cntry95.sbx cntry95.shp cntry95.shx
· plat_lin.dbf plat_lin.sbn plat_lin.sbx plat_lin.shp plat_lin.shx
· plat_pol.dbf plat_pol.sbn plat_pol.sbx plat_pol.shp plat_pol.shx
· plates_4types.avl plates_4types.dbf plates_4types.shp plates_4types.shx
· quakes2001.dbf quakes2001.sbn quakes2001.sbx quakes2001.shp quakes2001.shx
· world30.dbf world30.sbn world30.sbx world30.shp world30.shx
1) What extension do the files that contain the maps have?
2) What extension do the files that contain the tables have?
3) Are the tables the "G" or the "I" or the "S" part of GIS?
4) What role do the files that have the other extensions play in GIS?
Note that these are shapefiles, one of many common GIS data structures. Others include geodatabases, raster grids, and images.
Start ArcGIS and ArcMap with a blank map document.
Add all of your layers as identified above: countries, plate lines, plate polygons, plates 4 types, quakes 2001, and world30.
Save your map document as earthquake.mxd in your working folder.
Use View à Data FrameàCoordinate System to set your coordinate system to Geographicà Worldà WGS 84.
5) Why is it important to establish a coordinate system for your data?
6) Examine the pattern of earthquakes and make two spatial observations.
Note how all the earthquake epicenters are the same color. Change this so that earthquakes are mapped with the color indicating the magnitude. Right click on layer, and look under Propertiesà Symbology.
Change the symbology type from “single symbol” to “quantities.” Select the Magnitude Field. Add All Values.
7) Describe the pattern of earthquakes mapped by magnitude.
Open the table for the earthquake data and sort on magnitude. Zoom to the largest earthquake in terms of magnitude.
8) Where did the largest earthquake in the data set occur? What was its magnitude? Was it on land or underwater?
9) Approximately what percentage of the earthquakes in this data set would you estimate are underwater?
10) What is the major concern with underwater earthquakes?
11) Can you find any aftershocks from any of earthquakes in the data? How would you determine if they were aftershocks?
12) If you find one, where was it and how many aftershocks occurred?
Make a map symbolized on depth (in kilometers underneath the surface) of earthquakes.
13) Where did the deepest earthquake in the data set occur? What was its magnitude?
A subduction zone is a zone where one plate is subducting, or moving under, another plate. One subduction zone is along the west coast of South America.
14) What plate is subducting under what other plate?
15) In North and South America, where do the deepest earthquakes occur? Why?
16) Is there a relationship between magnitude and depth? Why or why not?
Examine the plate lines and plate polygons data sets.
17) What are the features in these spatial data sets?
18) On what tectonic plate do you live?
Examine the plates 4 types data set.
19) What is the major difference in the attributes of the two layers plat_lin vs plates_4types layers?
20) After zooming and panning these two data sets (plat_lin and plates 4 types), which would you say was collected at a higher spatial resolution?
21) Do you detect any pattern of earthquake epicenters and magnitude related to the type of plate boundaries? If so, what is it, and where is the pattern most pronounced? If you have time, you might access information on:
s.gov/publications/text/understanding.html , or
reeman.com/bolt/con_index.htm?07 , or other plate tectonics site.
Proximity Analysis
Next, further investigate the relationship of plate boundaries and earthquakes further. With a GIS, you can determine the distance of points, lines, and polygons from each other. Here, you will determine how many epicenters are within a certain distance of the plate boundaries.
First go to the data frame properties. Note the map units.
22) What are the map units, and why?
Set the display units to kilometers.
Because you will perform a spatial query next, clear any and all selected features in each layer. For the next step, use the plate boundary data set that you indicated earlier was created with a higher spatial resolution.
23) Select epicenters that are within 200 km of plate boundaries by using Selectionà Select by Location. Indicate what you chose in the dialog box to accomplish this task.
24) What percentage of epicenters during 2001 were within 200 km of plate boundaries? Show your work.
25) Clear the any selected features in any layers. Repeat the above spatial query using the plate line file that has a lower resolution. Compare the results of the percentage of epicenters that are within 200 km of plate boundaries using this different plate line dataset.
26) Why might the results be different depending on the data set used? Discuss any data quality and scale issues related to the data layers you are examining that may have a direct bearing on your answer to the previous question.
27) What is difficult about the current map projection in conducting any study of the entire Pacific Ocean basin? Perhaps a map projection centered on the Pacific Ocean would be better. This is something to note for the future but you will not project the data in this activity.
Creating New Data
Say you work for the US Aid Disaster Relief team. You need to focus on the countries that contained the most earthquakes in 2001. To solve this problem, first examine the table associated with the 2001 earthquakes.
28) Does this table indicate which country the earthquakes occurred in?
Therefore, you need to join the country information from the country shape file to the earthquakes data so that you can determine which earthquakes were inside each country. This is a spatial join, not a tabular join; that is, “Join data from another layer based on spatial location” as follows. Right click on the quakes2001 layer and go to Joins and Relates. Join quakes2001 to the cntry95 table. Take the defaults in #2 and in #3, give the output a meaningful name, such as countryeq2001.shp:
29) Is your new layer a point or a polygon layer?
30) Examine the table in your new layer and make statements that compare the new layer table to the table associated with the original cntry95 layer.
Right-click on the field “cntry_name” and summarize. Save to the table quakessum in your folder. Sort the new table on “count of country name”.
31) Which country had the most earthquakes in 2001, and how many were there?
32) What does the count in the FIRST row of the summary table represent?
33) How many earthquakes did Chile experience in 2001?
34) Examine the map. What state or region in the country with the most earthquakes contributed the most earthquakes to that country?
Perform a spatial join and join your summary table to the cntry95 attribute table. Symbolize countries based on the number of earthquakes that occurred there.
35) What patterns do you notice in earthquakes by country? Why?
Save your map document.
Study Earthquakes Near Denver
Use the dot tool on the drawing toolbar (you might need to access Viewà Toolbars and make sure the drawing toolbar is on) and add a dot at the approximate location of Denver, Colorado at latitude 39.8 N and longitude 105 W. First, access the draw toolbar and choose the marker tool:
Left click in the approximate location of Denver on the map, and then after the dot is placed, right click, and access the properties of your new graphic element. Under position, type in the correct latitude and longitude in the x and y fields, and your dot will move to the correct position of Denver, at 105 west longitude and 39.8 north latitude:
Next, use the circle tool to draw a circle outward from Denver, Colorado. Increase the size of the circle until it intersects the first epicenter, noting the radius in the lower left of your screen.
36) Answer the following questions about the closest earthquake to Denver in 2001:
· What direction was it from Denver?
· How far was it from Denver?
· What was its magnitude?
· When did the earthquake occur?
Save your map document.
Downloading, Formatting, and Analyzing Point Data within a GIS
First, you will download information about earthquakes from the USGS National Earthquake Information Center that have occurred over the last several days. After you have the data, you will map these earthquake epicenters as point data. Before uploading the data into your GIS, you will need to edit the epicenters file.
Follow these directions closely and make sure to save all your Internet data in your working folder.
Go to the USGS National Earthquake Information Center:
http://ear thquakes.usgs.gov – and select Earthquakes à Get real time earthquake data à on the earthquake feeds page, scroll down to the Last 7 Days of Earthquakes and for significant earthquakes, select the CSV file. Open the CSV file.
The data that you will see will have this format:
DateTime,Latitude,Longitude,Depth,Magnitude,MagType,NbStations,Gap,Distance,RMS,Source,EventID,Version
2013-02-13T00:10:14.271+00:00,38.028,-118.053,12.4,5.1,ml,22,124,0.2,0.13,nn,nn00402688,1360781577612
2013-02-12T02:57:51.370+00:00,41.308,129.076,,5.1,mb,178,39,3.3,0.82,us,usc000f5t0,1360702130142
2013-02-10T18:39:35.830+00:00,-10.978,165.444,35.0,6.3,Mwp,175,39,5.6,0.87,us,usc000f4zf,1360695782000
37) Does the number of earthquakes over the past 7 days surprise you?
38) Can you visualize where these earthquakes have occurred? (That’s why we will map it!)
Before we do, notice the negative latitude and longitude readings.
39) How would 125.05 degrees east longitude be indicated within ArcGIS? ____
40) How would 125.05 degrees west longitude be indicated within ArcGIS? ___
41) How would 17.50 degrees south latitude be indicated? __________
Save the data on screen as a csv file – comma separated value; a data table.
Your data is now ready to bring to ArcGIS.
Now, you want to map your earthquake data. In your ArcMap document, under tools, select “Add Data.” Select your last 7 days of earthquakes data table.
Open your data table.
42) Think about the Cartesian Coordinate System. What field is the X coordinate—longitude or latitude?
After you see your last 7 days table in the table of contents on the left, right click on it and use “Display XY Data”. Complete the dialog box that appears, indicating the correct fields for longitude and latitude as x and y, respectively, and indicating that the incoming data is in Geographic WGS 84. You will get a warning that the data is not a GIS database, which is fine – because so far, it is just a data table that you are mapping.
If your table does not map, you probably have a misplaced or missing comma, or some other character that should not be there. You’ll need to check the table in WordPad or Excel, delete the table from the map document, re-add the table using Tools à Add XY Data.
Now you are ready to analyze the data you have mapped and draw some conclusions about it.
43) Change the symbology and map on magnitude. Where was the most severe earthquake over the past week?
44) Where was the deepest earthquake over the past week?
45) How far from your workplace was the closest earthquake during the past 7 days? Indicate the units you are using.
46) How well does the pattern of last week’s earthquakes match that of the 2001 earthquakes?
Now you are ready to create a final plot of your data. All the information you wish to include in the final plot will be in a "layout view." Access the layout view by selecting the button on the lower left of the map view.
You may also want to use Customize à Toolbarsà Layout to show the layout tools.
Under the Insert pull down menu, add the following:
A scale bar in kilometers, a title, your name, and the date.
47) Capture your layout as a screen shot and embed it in these lab sheets.
Save your map document.
48) What is the full drive and path name where your map document resides on your computer?
Synthesis
49) List three spatial observations about the extent and location of earthquakes that you have learned during this lesson.
50) Summarize in a few sentences what you have learned about GIS or spatial data in this lesson.
u End of Earthquakes Lesson.
Earthquakes Everyday: Using GIS to Analyze Global Plate Tectonics - Page 11 of 11
Author: Joseph J. Kerski –
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