EARTH 520
Plate Tectonics and People

Greek Earthquake Problem Set

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Now you are going to use the USGS Web site to find out some earthquake parameters using their database of publicly available earthquake data. Since we started out this lesson by discussing the particulars about an interesting tectonic regime in ancient Greece, let's stay in Greece and find out some things about its more recent tectonic activities.

Part 1 - General questions about an earthquake in Greece in 2008

Go to the USGS Latest Earthquakes Map and follow my directions as a screencast or as plain text. We are looking for a magnitude 6.4 earthquake that happened in Greece on June 8, 2008.

  1. Create a word processing document (Microsoft Word, Macintosh Pages, Google Docs, or PDF) to record your work for this problem set. What was the location of this earthquake (latitude, longitude, depth)?
  2. Click the ShakeMap button and/or the DYFI (Did You Feel It?) button and answer: About how far was this earthquake from Delphi? What was the estimated intensity of ground shaking that was felt at Delphi from this earthquake? See Figure 1 in the de Boer et al. Geology paper for a map showing the location of Delphi.
  3. Calculate energy released for this event.

Part 2 - Aftershocks of the 2008 Greek earthquake

I want you to learn to use the various earthquake search features that the USGS provides. If you took EARTH 501, then you know something about this already. In this part of the activity, we'll use the search feature to find aftershocks of the mag 6.4 event we found in Part 1.

Go to the USGS Latest Earthquakes Map and follow my directions as a screencast or as plain text.

Answer the following questions. Record your answers in your word processing document.


  1. How many earthquakes did this search find?
  2. What was the biggest event (not including the mag 6.4 main shock), and how many are there of this size? Does this observation support Båth's Law?
  3. Make a plot that compares the aftershock data you found for this earthquake to Omori's law. Note: I think the easiest way to do this will be to count the number of aftershocks each day and plot that number vs. time. Then put another line on your plot that shows the ideal Omori relationship. That way you can compare the two. (If you have trouble getting started with this, post to the "Questions" discussion board.)
  4. Does the number of earthquakes in this region decay with time as Omori's Law predicts? Discuss the observations suggested by your plot. If you did not find an Omori-type relationship, what are some possible reasons?
  5. What assumptions did we make that may or may not have been valid when we looked for aftershocks using this search feature?
  6. Make an educated guess about the background rate of seismicity in this area. How did you decide?

Part 3 - Aftershocks of the 2011 Great Tohoku earthquake

Let's look at the aftershock sequence of the Mw 9.0 earthquake of 11 Mar 2011. Here's a link to the USGS map of aftershocks. Also, I made an animation of a two-month time window centered on the earthquake, using an exponential scale for symbol size since that is closer to accurate. Let's go through a similar exercise as with the Greek earthquake and see how well Omori's Law works in this case.

Go back to the USGS Latest Earthquakes Map and follow my plain text directions.

Answer the following questions. Record your answers in your word processing document.

  1. When did you decide to end your search (how many days had elapsed after the mainshock)? How many earthquakes did your search find? Do you think you found all the earthquakes in this aftershock sequence? More? Fewer? Why?
  2. Make a plot that compares the aftershock data you found for this earthquake to Omori's law.
  3. Does the number of earthquakes in this region decay with time as Omori's Law predicts? Discuss the observations suggested by your plot. If you did not find an Omori-type relationship, what are some of the reasons?
  4. Can you tell what the background seismicity rate is for this area? Why or why not?
  5. Compare the aftershock sequence for this event to the one you observed for the Greek earthquake. Does this sequence merely look exaggerated (because the mainshock was so much bigger) but otherwise the same or are there other significant differences? What I am driving at is for you to try to decide whether you can verify the idea that aftershock sequences are scale independent. I know we are only comparing two sequences instead of a statistically meaningful number, but it is still worth thinking about.

Part 4 - Find your own earthquake

The point of this part of the problem set is for you to learn how you can adapt the catalog search features offered by the USGS for your own use. What better way to do this than to find the most recent earthquake closest to where you live? Here's how:

Go back to the USGS Latest Earthquakes Map and follow my plain text directions.

Answer the following questions. Record your answers in your word processing document.

15. What was the date of your earthquake?

16. What was the location (latitude, longitude, depth) of your earthquake?

  1. What was the magnitude of your earthquake?
  2. How close was this earthquake to where you actually live? Did you feel it? If there is a DYFI map, check it out and see if anybody else near you felt it.

Save your word processing document and name it like this:

L7_greek_earthquake_AccessAccountID_LastName.doc (or your file extension).

For example, former Cardinals right fielder and hall of famer Enos Slaughter would name his file "L7_greek_earthquake_ebs9_slaughter.doc"

Submitting your work

Upload your file to the Lesson 7 - Greek earthquake problem set assignment in CANVAS by the due date indicated on the first page of this lesson.

Grading rubric

I will use my general grading rubric for problem sets to grade this activity.