VEPP: "Doing Science" in General Education, University Earth Science Courses: Patterns of Seismicity at Plate Boundaries

This is an exercise that is in development and has not yet been fully tested in the classroom. Please check back regularly for updates and changes.

General education courses for non-science majors at many universities are emphasizing active learning methods that attempt to reproduce the process of doing 'real' science, rather than focusing on 'learning' a large body of factual material. Learning outcomes often require a 'research' project in which students define a problem or formulate a hypothesis; find, access and analyze data; and use their analytical reasoning and critical thinking skills to arrive at an independent conclusion.

The distribution of seismicity, heat flow, and magmatism on Earth were the fundamental observations in constructing the plate tectonics paradigm. Essentially, the intent of this project is for students to assemble the relevant data that were used to define plate boundaries and gain insight into plate boundary processes as was done by geophysicists and geologists to prove plate tectonics.

Brief description

This exercise uses a spreadsheet to organize, plot and analyze data acquired from the IRIS Earthquake browser or the Advanced National Seismic System earthquake catalogs to define, compare, and contrast the geometry of two different subduction zone-volcanic arc systems.

Full description

This project is an example of the type of activity that will be required for satisfying learning outcomes associated with a general education (100 level, freshmen non-science major) course in Intellectual Inquiry in the Natural Sciences at the University of Kentucky.The learning outcomes require that students demonstrate the ability to complete a project using scientific methods that includes design (hypothesis formulation, problem statement), data collection (primarily using original databases), data manipulation and analysis (graphical, statistical, quantitative), making inferences and drawing conclusions, and oral and written presentation of their results to peers. The classes in which this exercise will be used have 100 students, a lecturer, two TAs, and a 2:1 lecture:recitation format (25 students/section). Lecture will provide time to present relevant content and review use of relevant software and web pages. The project is intended to be completed in the last 4 weeks of the term, so that

The example presented here uses world-wide earthquake location catalogs to analyze the variation in subduction zone geometry (e.g., angle of subduction) and crustal structure at ocean-ocean and continent-ocean plate boundaries. The question that serves as the basis for this example is: "What are the factors that control the distance from the trench to the volcanic arc in convergent oceanic-continent plate settings?" Two subduction zones are used as the basis for comparison and illustration here (Chile and Tonga-Kermadec). This admittedly simple project is merely a starting point for an introductory class. However, more creative and ambitious students could use the wealth of data available at the VEPP website for their project.

Two earthquake catalogs are recommended, based on ease of use of the interface and ability to output data to a format that can be imported into Excel.

The IRIS Earthquake Browser (http://www.iris.edu/servelet/eventserver/map.do) is a graphical interface that is the simplest to use and most instructional. The user immediately sees the location of their study area, and can select a Google Earth satellite view to show topography and bathymetry. The interface allows the user to define a boxed area on a world map at various scales and zoom levels. The user can also define specific time, depth, and magnitude limits. Visual output is in the form of a map of earthquake epicenters, color-coded by depth (click on thumbnail below to see full screen image). Such graphical output is very instructive in its own right! However, for 'real' data analysis, output is also possible in comma- and space-delimited text format that can be opened in Excel. Such data will need to be "cleaned up" ('text to columns', depths converted to negative numbers for plotting) for manipulation in Excel. A maximum of 5000 points can be downloaded from the IRIS site.

The Advanced National Seismic System (ANSS) has a simple interface that allows the user to input the boundaries of the area of interest, but those boundaries need to be known before hand, i.e., students need to know the bounding latitudes and longitudes beforehand (lat-long and other map principles can be covered in class). The user can also specify limits for earthquake magnitudes, a time window, and a depth limit. Up to 10000 earthquake locations can be downloaded. The ANSS interface looks like this:

Several iterations of sizing the data set will probably be necessary. 5000 (IRIS) or 10000 (ANSS) points are probably not necessary for seeing trends in data!

Click on the thumbnails below to see the distribution of earthquakes as a function of depth in central Chile and the northern Tonga-Kermadec subduction zones:

The Andean arc is 2.81 degrees longitude east of the Peru-Chile trench, and the Kermadec arc is only 1.23 degrees west of the trench (determined from line length function in Google Earth). This should reflect differing angles of subduction.

There are several other on-line sources of information and data relevant to earthquakes and seismic hazards that students could use to place their study in a relevant context:

U.S. Geological Survey Earthquake Hazards Program: http://earthquakes.usgs.gov/

Another earthquake search option is available at the U.S.G.S./National Earthquake Information Center. This site is sort of middle ground between the IRIS graphical interface and the ANSS site. Results of an area search can be output to a map or a comma-delimited text file.

http://earthquake.usgs.gov/earthquakes/eqarchives/epic/epic_rect.php