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 below. We are looking for a magnitude 6.4 earthquake that happened in Greece on June 8, 2008.

My directions:
  • Go to earthquake.usgs.gov

  • Click the settings icon, which looks like a bike sprocket in the upper right corner of the page.

  • Scroll down in the settings menu to the Search Earthquake Archives bar and click it

  • Under Magnitude, enter 6 as the minimum magnitude

  • Under Date & Time, enter 2008-06-08 as the start date and 2008-06-09 as the end date

  • Under Geographic Region, select World

  • Don't change anything else.

  • Scroll down and click Search

  • There's your earthquake. It should be the only one on the map. Click the circle on the map where your earthquake is located. Now a pop-up box appears in the bottom left corner of the page with a link that says M 6.4 - southern Greece. Click that link.

  • You'll be taken to a page that has lots of scientific information about this earthquake. All the questions I ask you in this part of the problem set are found there, or can be figured out from information that is there.

  • Create a word processing document (Microsoft Word, Macintosh Pages, Google Docs, or PDF) to record your work for this problem set.

Part 1 questions:

1.1 What was the location of this earthquake (latitude, longitude, depth)?

For 1.2 and 1.3 you should look at the ShakeMap and Did You Feel It? links.

1.2 About how far was this earthquake from Delphi? (See Figure 1 in the de Boer et al. Geology paper for a map showing the location of Delphi.)

1.3 What was the estimated intensity of ground shaking that was felt at Delphi from this earthquake?

1.4 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 below.

My directions:
  • Go to earthquake.usgs.gov
  • Click the settings icon, which looks like a bike sprocket in the upper right corner of the page.
  • In the settings menu, scroll down and click the bar to Search Earthquake Archives
  • Under Magnitude change minimum magnitude to 0.
  • Under Date & Time enter 2008-06-08 as the start date and enter 2008-12-31 as the end date
  • Under Geographic Region choose World
  • We will use the circle/donut search feature to look for aftershocks. Click to expand Advanced Options. Where it says Circle type the earthquake's latitude and longitude into the boxes designated Center Latitude and Center Longitude. Make the Outer Radius 100. Leave everything else blank.
  • Scroll down and click to expand Order Options. Select Order By Time - Oldest First
  • Click Search.
  • There's your map and list of earthquakes.
Part 2 questions

2.1 How many earthquakes did this search find?

2.2 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?

For 2.3, you will want to download the list of earthquakes. Do so by clicking 'Click for more information' at the top of the list.

2.3 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.)

2.4 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?

2.5 What assumptions did we make that may or may not have been valid when we looked for aftershocks using this search feature?

2.6 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. If you want to check it out, 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 directions.

My directions:
  • Go to earthquake.usgs.gov
  • Click the settings icon, which looks like a bike sprocket in the upper right corner of the page.
  • In the settings menu, scroll down and click the bar to Search Earthquake Archives
  • Under Magnitude change minimum magnitude to 2.5.
  • Under Date & Time, enter 2011-03-11 05:46:24 as the Start date and 2011-03-12 05:46:24 as the End date. This gives you a day of aftershocks.
  • Under Geographic Region, choose Custom
  • Click to expand Advanced Options and under Geographic Region enter 42 in the North box, 34 in the South box, 140 in the West box, and 146 in the East box.
  • Click to expand Output Options and choose Map and List as the FORMAT and Time-Oldest First as the ORDER BY option.
  • Click search.
  • Take note of the number of events plotted on the map. This is the number for day 1 of your Omori plot.
  • Redo the search changing nothing except under Date & Time enter 2011-03-12,05:46:24 as the Start date and 2011-03-13,05:46:24 as the End date. This gives you the second day of aftershocks.
  • Click search.
  • Take note of the number of events plotted on the map. This is the number for day 2 of your Omori plot.
  • Keep going until you think you have enough data to interpret your plot.
Part 3 Questions:

3.1 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?

3.2 Make a plot that compares the aftershock data you found for this earthquake to Omori's law.

3.3 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?

3.4 Can you tell what the background seismicity rate is for this area? Why or why not?

3.5 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 below.

My directions:
  • Go to earthquake.usgs.gov
  • Click the settings icon, which looks like a bike sprocket in the upper right corner of the page.
  • In the settings menu, scroll down and click the bar to Search Earthquake Archives
  • Under Basic Options, change minimum magnitude to zero
  • Under Date & Time enter a time several years ago as the Start date and leave the default (today's date) as the End date.
  • click where it says Draw Rectangle on Map and draw a rectangle around your state if you are in the US, or some other reasonable regional size if you live outside the US. It is helpful to use the + - buttons to zoom in first.
  • Once you like your rectangle, click Use This Region.
  • Choose Map and List as the FORMAT
  • Click search

If your search returns nothing, choose a bigger region or else make the start time a few years earlier. If your search turns up a huge number of earthquakes you may want to do it again with a smaller region or a shorter time window.

Choose the earthquake closest to where you live, or a different one that looks exciting, and answer the Part 4 questions.

Part 4 questions:

4.1 What was the date of your earthquake?

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

4.3 What was the magnitude of your earthquake?

4.4 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.