Earthquakes and Hazard

This exercise examines the global nature of earthquakes and their hazards.  NOTE:  These exercises need not be completed in order!

Part I - Earthquake Histories

Double-click on the "Seismic" (not "Seismic wave") simulation on your desktop.  This simulation, by Dr. Alan Jones of SUNY Binghamton, displays a global catalog of earthquakes across selected times and areas.  You could spend all day on this exercise alone, but please be sure to do at least the exercises below.  Be aware that you can:

• turn earthquakes and volcanoes on and off,
• change the threshold values for recording,
• change the "play" speed
• turn the sound effects on and off, and
• pause and step forward (or back) to get data on specific events.

Exercises:

• From the "World" button on the world map:  over the ~ 8 years of data:
  • How many M>8 earthquakes were there?____  M>7? _____  M>6?   M>5?
  • How many E>4 volcanic eruptions were there? ____  E>3?  _____ E>2?____   E>1? ____
  • How large are the largest earthquakes along mid-ocean ridges? _____  Along subduction zones?  _____  Why are they different?

   

• From the North America / Alaska / Alaska 1964:
  • What explains the pattern across space of the recorded earthquakes?

   

  • Is there a pattern across time as well?  Why (not)?

   

  • How about a pattern of earthquake size?  Why (not)
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• From North America / Alaska / Cook Inlet
  • What pattern is evident here?

   

  • How does it relate (if at all) to the 1964 earthquake 20 years earlier? 

   

  • How does it relate to volcanoes along Cook Inlet?  HINT:  Try the Cook Inlet cross-section and 3-D views after you look at the map view!

   

• From North America / United States:
  • Where are earthquakes most common? ___________  At what depth? __________   What is the common focal depth at offshore earthquakes along the same trend? _________  Why?

   

  • Where else are earthquakes common?  NOTE:  Pause before October 28, 1983.   How does your answer differ before and after that date, and why?

   

  • Where are earthquakes rare (several places)?  Why might they occur in those places?

   

  • Where are no earthquakes recorded?  What does this suggest about the hazard there?

Part II - Earthquake Location

California State University at Los Angeles has designed a "Virtual Earthquake" Web site which talks you through how earthquakes are located in 2 dimensions.  Access the site.  Follow the instructions to become a virtual seismologist!  Note:  If you want to print your diploma, make certain you don't wait 'til the end of lab!

Part III - Recent Earthquakes

The Incorporated Research Institutions for Seismology (IRIS) maintains a near-real-time Seismic Monitor site on the Web.  It is updated every 30 minutes, and shows recent earthquake epicenters as well as monitoring stations around the world.

Select a monitoring station (or two, or three), shown by purple triangles, to learn something about seismic monitoring.  How many seismometers are required at each station?  How (and where) are the stations constructed to minimize unwanted noise?

Select a recent earthquake.  A catalog will come up of all recorded earthquakes in the past 30 days.  How large was the largest, and where was it located?  How small was the smallest, and where was it located?  How complete do you think this record is, and why?

In addition to the bold highlighting of your selected earthquake and its neighbors, fainter highlighting identifies linked major earthquakes.  Follow one of those.   Examine the seismograms, looking especially for the time difference between P and S wave arrivals (see Part II).  How long did it take for the P waves to reach the farthest monitoring station shown on the world map?  Given that the world is about 40,000 km in circumference, what does that suggest for an approximate velocity for P waves?  What is wrong with that estimate?