SO262, Fall 2018

In Class Exercise--Volcanoes and Earthquakes

We have a number of data sets, some in several versions that allow different manipulation in Google Earth (download if needed).  You should be careful about loading all of them, as Google Earth may not be very responsive if you try to display them all at the same time.

Quick guide to Google Earth commands.

USGS Plate Boundaries. 
Extracted from the KML displays of current seismic activity at USGS which credited the boundaries to Peter Bird of UCLA.

USGS Quaternary (< 1.6 MA) faults of the western US.

They are sorted by age categories.

Smithsonian volcano database.  

This sorts volcanoes into stratovolcanoes, shield volcanoes, and others.  There is another version on the web which has pictures of each volcano, and a description.
Megathrusts.  These come from USGS.  They show all the earthquakes around one of the megathrusts, in both time and location.  Sorted by Magnitude
Time animations
CMT earthquake catalog.  This indicates both the type of fault, and the magnitude using a slightly different scale than in the USGS catalog above. Earthquake focal mechanisms.   This sorts the earthquakes into thrusts, normal faults, and strike slip faults.  There are also oblique faults, with a combination motion.  The types are differentiated by the stylized beach balls and colors.  Particularly for smaller earthquakes far from land and seismic stations, the locations may only be approximate.
MB Magnitudes.   This uses MB, one of several magnitude scales used by hard core seismologists.  Particularly for the very rare, very large events, it is very hard to have a single scale which also works well for the much more frequent smaller events and the true monsters.  You will note there are minor differences between these magnitudes and those in the megathrust data above.

This is group effort, in teams of 1, 2, or 3.  You are to answer one of the following 5 questions for each member of your team in a Word document.  This is a writing assignment, and not just answering the questions.  Your answer should not refer to the questions, and not require knowing the questions to make sense.  For each, you should have several maps to support your answers to the questions.  The due date is on the course syllabus.

Option 1.  Look at the Mid Atlantic Ridge. The plate boundaries have several colors (mainly blue, green, and red) and no legend (but in the table of contents you will see something which explains them).
USGS Plate Boundaries
Earthquake focal mechanisms.
MB Magnitudes.  
  • How many types of plate boundary occur there, and how many kinds of faults? 
  • Can you correlate the fault types with different boundary segments? 
  • What are the magnitudes of these earthquakes, and how do they compare with other environments?  You might want to do a quick display showing where the largest earthquakes are, and progressively add smaller ones.  Use the CMT catalog.
Option 2. Look at the earthquakes in the time periods of the three megathrusts of the recent past.
Earthquake focal mechanisms.
MB Magnitudes
  • What kind of plate boundary is associated with each?
  • What does the dominant type of fault appear to be in the region?  Use the CMT catalog.
  • Are there volcanoes associated with each megathrust, and if so, what is the dominant kind?  Look at the broad picture, and determine how close to earthquakes the volcanoes are.
  • What length along the fault ruptured in each case?  You should clearly be able to see the increase in earthquakes  compared to more distant regions; this is the region that slipped during the earthquake and the aftershocks.
Option 3. Look at the Big Island of Hawaii, and the Cascade volcanoes in Oregon and Washington.  Include the USGS Quaternary faults
USGS Plate Boundaries
USGS Quaternary (< 1.6 MA) faults of the western US
Smithsonian volcano database
  • Get 3D views from Google Earth for one volcano in each location, and discuss the differences in size and shape of the volcanoes.
  • Does either type of volcano appear to be related to faults?  If so, can you recognize the faults in the 3D views of the landscape?
Option 4. Look at the Great Basin in the Western US (the state of Nevada, eastern California, and western Utah).
MB Magnitudes
USGS Plate Boundaries
USGS Quaternary (< 1.6 MA) faults of the western US.
  • What is the pattern of faults?  How do they relate to the mountains and valleys (another name here is Basin and Range)?
  • Does this area have a lot of earthquakes?  What kinds of faults produce them, and how big are they?
Option 5. Look at the East African Rift running SW from Ethiopia past Lake Victoria to Lake Malawi.
USGS Plate Boundaries
Smithsonian volcano database
  • There is a plate boundary shown there.  Based on the color, what kind of boundary is it?
  • Is the dominant volcano type stratovolcano or shield volcano?  Does this match the plate boundary above?
  • What is the dominant kind of fault is this region?