Exploring North American Earthquakes
By Joseph J. Kerski
Part 1: What's Shakin?
In this part, you will examine earthquakes across North America, noting their distribution, magnitude, and depth, and also examining certain regions on the continent.
After accessing the Global GIS interface, you will be viewing the "G" part of GIS with the map on the right side and a set of tools across the left and the top.
Turn off (uncheck) all themes except for the following:
- shaded relief base (at the bottom of the table of contents)
- earthquakes 1973-1994 (about 1/3 down on the table of contents)
Access the Movies, 3D menu at the top and run nam_eq_anima.avi. Use the slider bar to position the movie at specific years you wish to investigate further.
- What years do the earthquakes cover?
- The USGS seismologists want you to make three observations about the spatial pattern of earthquakes that you notice as they occur across the North American continent. Consider the extent of the earthquakes, and specific areas of North America where earthquakes occur more often.
- Make three observations about the magnitude of earthquakes and where earthquakes of certain magnitudes occur across North America. Do large earthquakes only occur in specific regions? If so, where are they?
- Do any specific years seem to have more earthquakes than others, or would you say that about the same number of earthquakes occur each year?
Close the movie and return to your GIS. Now you can further analyze the earthquake theme and draw some conclusions.
- Do more earthquakes occur near oceans or in the interior of the North American continent? Why?
- Do more earthquakes occur near the Pacific Ocean to the west of North America or near the Atlantic Ocean to the east of North America? Why?
- Compare the number of earthquakes that occur in the oceans versus land.
- Compare the Atlantic versus Pacific Ocean earthquakes.
- What feature runs down the middle of the Atlantic, and why is it so prone to earthquakes?
- What particular hazard exists to people when an earthquake occurs in the ocean?
- In what part(s) of North America would people need to be concerned about earthquakes occurring in the ocean?
Make volcanoes visible by checking the box to the left of the theme name .
- Make three observations about the pattern of volcanoes in North America.
- The USGS wants you to determine the relationship of earthquakes and volcanoes. Examine at least three different places around North America and investigate the spatial relationship between earthquakes and volcanoes. Do volcanoes and earthquakes occur in the same places? Include the three places you examined, your conclusions about the relationship, and why you believe the relationship either exists or does not exist.
Single click on the earthquakes theme so that it becomes raised up, or “active.”
Each row in the table represents one earthquake in the dataset.
- Look in the upper left part of your screen under ArcView GIS. How many earthquakes are recorded in this dataset?
- Approximately how many earthquakes are recorded during an average year? Show how you determined this answer.
Click on the "magnitude" field and sort it in descending order .
Navigate to the top of the table and click on the row containing the earthquake with the highest magnitude to select it. You may have to select the black selection arrow to select a row . The row will appear in yellow.
- What is the magnitude of this earthquake?
Close the table. In the Global GIS Tools box, on the right side of Viewing Tools, go to “More Tools.” Select the "Zoom to Selected" tool in the Global GIS Tools box:
Use the "zoom into center" button a number of times to zoom into your selected earthquake .
Turn on the themes political boundaries, and political boundary labels.
- In which country did the largest earthquake occur?
Access the earthquakes table again and clear your selection .
Select the field "km" in the table. This represents the depth of the earthquakes in kilometers underneath the surface.
Click on the "km" field and sort it in descending order . Navigate to the top of the table and click on the row containing the earthquake with the greatest depth to select it . The row will appear in yellow.
- What is the depth of this earthquake?
Close the table and select the "Zoom to Selected" tool in the Global GIS Tools box . Use the "zoom into center" button a number of times to zoom to your selected earthquake .
- In which country has the deepest earthquake occurred?
- In what continent is this country?
Pan to the United States.
- You are asked to list in your USGS report that states you consider to be most vulnerable to earthquakes. List the top three states, and your reasons for including them.
Pan to the western side of the United States to the area of California. You could turn on the US Counties theme to see California counties all in the same color.
- You receive an email from the USGS seismologists that ask you to determine four major areas of California where most earthquakes occur. What four areas will you list in your report?
Turn on major cities and turn off earthquakes. You might have to zoom in to see the labels.
Zoom to the center of the Pacific Coast of the United States, central California and Nevada.
Use the "Create Profile" tool and draw a line from Carson City, Nevada, southwest to San Francisco, California. Choose to profile the data set “elevation.”
- Describe how the land elevation changes from Carson City to San Francisco.
Turn earthquakes back on.
- Examine the earthquakes across your profile. What kind of terrain is more prone to earthquakes—valleys or mountains? Why?
Zoom out to California, turn off earthquakes, and note the location and names of the 6 major cities. Turn earthquakes back on.
- Of the 6 major cities in California, indicate in your report to the USGS the 2 cities that you consider to be the most vulnerable to an earthquake. Indicate why you consider them to be the most vulnerable.
- Congratulations! You have completed the first part of the assignment and have contributed much to the understanding of earthquakes in North America. Indicate what you consider to be the most surprising thing you have learned in this part, the most interesting thing, and the most significant thing.