ISL #15Earthquake Patterns and Plate Boundaries

05/15Integrated Science 4 Name: Per: Objective

Use the IRIS Earthquake Browser to explore earthquake patterns at all three types of plate tectonic boundaries and identify their relationship to geomorphological features (mountain chains, volcanoes, trenches) associated with each plate boundary.

Procedures1. Global Seismicity: Preliminary ObservationsGoogle the following phrase to access the IRIS earthquake map: “iris earthquake browser”. You will use this web application to plot earthquake data. When you open the website, you will be presented with a map of the world and the 200 most recent earthquake events.

Try to zoom in on the map, move it around, and click on events to get more details about particular earthquakes. On the right-hand side of the window, try change the number of events, time, magnitude, and depth ranges of events that are displayed on the map. In the upper right-hand corner, try to change the view from geopolitical boundaries to satellite or terrain. Please note: Displaying large numbers of events (over 3,000) may cause browsers on slower machines to stall or freeze up. Keep this in mind when plotting data.

Questions1. How can you change the settings to give you a better idea of where plate boundaries may be?

2. How many large earthquakes (≥9.0 magnitude) have occurred in the past ten years (you'll need to change the time range – “earliest available” changes to today's date ten years ago)? How many ≥7.0 magnitude? How many in total (look at “events displayed xxx of xxx. The second number is the total)?

3. Where do the deepest earthquakes (≥300 km) tend to occur?

4. Switch to a satellite view of the world. Do earthquake patterns correlate with any visible features? If so, describe the correlations.

5. Which earthquakes are most common: deep or shallow?

2. Convergent Boundaries (Continent – Ocean Collision)

You will now explore the seismicity of a plate boundary between ocean and continental crust. In the lower left-hand corner, click "Select a region", then draw a box over Japan, including some of the nearby ocean. Select the following settings and click “Zoom to region”:Location: An area containing North Korea, South Korea, Japan, into Pacific OceanView: SatelliteDisplay: 1000 eventsTime Range: Set the dates to request 2 years of data (from this date last year through latest available). Magnitude Range: All ValuesDepth Range (km): All Values

You should get a map that looks similar to the one above (if you've been playing around with the magnitude and depth ranges, the numbers may not look exactly as above, which is fine as long as the "All Values" boxes are checked).

Questions6. How frequent are earthquakes in this region?

7. What is the depth distribution of the earthquakes? Is there a pattern in the earthquake depths? If so, how do you explain it?

8. Do the earthquakes correspond to any visible features in satellite view? If so, what are these features?

3. Divergent Boundaries (Mid-Ocean Ridge)You will now explore the seismicity of a divergent boundary in the central Atlantic, the mid-ocean ridge. Click "Select a region", then select a large area of the central Atlantic and click “Zoom to region”.Location: Middle of Atlantic Ocean (e.g. from eastern edge of Brazil to western edge of Guinea in Africa)View: SatelliteDisplay: 1000 eventsTime Range: Set the dates to request 2 years of data (from this date last year through latest available). Magnitude Range: All ValuesDepth Range (km): All Values

Questions9. How frequent are earthquakes in this region? How does this compare to the seismicity near

Japan?

10. What is the typical depth of earthquakes in this region? How does this compare to earthquakes near Japan?

11. How do you explain the differences in depth and frequency of earthquakes between the mid-ocean ridge and Japan?

12. Do the earthquakes correspond to any visible features in satellite view? If so, what are these features?

4. Transform Boundary (California's San Andreas Fault)You will now explore the seismicity of a transform boundary in California, the San Andreas Fault. Click "Select a region", then select a large area including California and all of Mexico click “Zoom to region”.View: SatelliteDisplay: 1000 eventsTime Range: Earliest available to latest available Magnitude Range: All ValuesDepth Range (km): All Values

Questions13. Do earthquakes in California tend to be deep or shallow?

14. Of the types of boundaries investigated earlier, which one best explains the pattern you see in Central America?

15. Why would earthquake depths be different in California and Central America?

16. How many large earthquakes of magnitude ≥7 occurred in California? In Central America?