Department of Earth Science |Northeastern Illinois University

INTRODUCTION TO EARTH SCIENCE
ESCI 121
Section 05
 Spring 2009

Review for Exam #4 (May 5, 2009)                                                                                                           Dr. Sanders

For the exam, you should be able to do the following:

VOLCANOES

w    Review: List the geotectonic settings in which volcanoes occur (subduction zones, divergent zones, hotspots).

w    Review: Tell why  volcanoes occur at each of these settings.

w    List the three general shapes of volcanoes and explain why they have the forms they do. 

w    Explain how viscosity of magma influences volcano shape/profile and eruptive style, and what determines the magma viscosity.

w    Tell what makes rock melt in the crust and mantle settings where volcanoes occur.  Describe the process in terms of changing temperature and pressure, introduction of "impurities" (water and sediments) into the melt, and draw a graph illustrating these varying conditions.

w   Explain how each of the above characteristics is influenced by the geotectonic setting of the volcano.

EARTHQUAKES

w  Explain the difference between the focus of an earthquake, and the epicenter. 

w  Tell what the term magnitude means as applied to earthquakes.

w  Possible extra credit opportunity coming soon: Describe the relationship, if there is one, between magnitude and focus depth of earthquakes.

w  Using the earthquake maps the class produced, arrange them in meaningful groups based on the patterns of earthquake epicenters and based on the patterns of focal depths you observe in each. 
 
EARTHQUAKE MAPS

w Using the earthquake maps the class produced, arrange them in meaningful groups based on the patterns of earthquake epicenters and based on the patterns of focal depths you observe in each. 

w Analyze a map illustrating earthquake epicenter locations and depth of focus.  Using the map, explain the area's relationship to geotectonics, and tell how and why the map has the appearance it has. 

MEASURING EARTHQUAKES

w Explain how a seismometer works.

w Explain why every seismograph includes at least three seismometers.

w Describe P-waves and S-waves and explain the differences between them.

w Explain why S-waves do not travel through liquids, and how this helps us understand the internal structure of the Earth (especially the outer core).

w Demonstrate how to use a seismic P-S lag (time difference) to determine the distance to an earthquake epicenter.

w Show how to locate the epicenter of an earthquake using seismograms from three different stations.  Explain why it is necessary to use data from at least three stations.

w After viewing some of the videos and animations of the Indian Ocean tsunami of December 26, 2004, research seismograms from the event.

w Use seismograms to find the epicenter of an earthquake using the Indian Ocean tsunami as an example.  (Extra copies of the map, the seismograms , and the P-S lag (time difference) graph are linked to this page.  This exercise is abridged from an exercise copyrighted in 2004 by Dave Robison and Steve Kluge.)
 
w Show how to locate the epicenter of an earthquake using seismograms from three different stations.  Explain why it is necessary to use data from at least three stations.  (You will need: map, compass, graph of P- and S-wave travel times, three seismograms for the event).

w After viewing some of the videos and animations of the Indian Ocean tsunami of December 26, 2004, analyze the seismograms from the event.

w Use seismograms to find the epicenter of an earthquake using the Indian Ocean tsunami as an example.  (Extra copies of the map, the seismograms , and the P-S lag (time difference) graph are linked to this page.  This exercise is abridged from an exercise copyrighted in 2004 by Dave Robison and Steve Kluge.)

w Use the results of your calculations to determine exactly when the earthquake occurred.

w Assuming that the Dec. 26, 2004 tsunami traveled at 600 km/hour (an average speed for tsunamis in the open ocean), estimate how long it would take to arrive at Indonesia, Sri Lanka, India, and Somalia.
 

Today's Challenge:  Find and analyze seismograms for the magnitude 6.3 earthquake in Central Italy Monday, April 06, 2009 at 01:32:39 UTC.  (What is UTC?)
Follow the three steps below.
First:  Use the "Rapid Earthquake Viewer". 

Go to http://rev.seis.sc.edu/ .  (If you want a tutorial, scroll down; you'll find it under "Educational Links of Interest", on the DLESE Teaching Boxes page.)  Click "Earthquake View", and on the map, select the Central Italy earthquake of April 6, 2009.  Be sure to choose the one with a magnitude of 6.3 !!

Next, you'll see seismograms for 10-12 monitoring stations.  Click the different options under "Seismograph Orientation" to see what happens to the seismograms.

 Go to the class wiki and log in.  On the Rapid Earthquake Viewer page, choose one of the monitoring stations; the station name appears below the seismograms.  On the wiki page, sign up for your choice.

Scroll to the list of station codes and click yours.  You will see three seismograms from that station.  (What is the difference between them?)  Click "Overlay estimated P wave/S wave arrival times".  You may want to "Select Zoom" to zoom closer to either the P wave or S wave.

Determine the exact P-S time lag (time difference).  Fill in all the values in the table on the wiki page. 
 
Second:  Use the IRIS BUD page.

Open this page: http://www.iris.edu/bud_stuff/bud/bud_start.pl?BUDDIR=/budnas/virtualnets/ALL
A help page is available at  http://www.iris.edu/bud_stuff/dmc/help.htm . 
For more help on picking out P and S waves, see "How Do I Read a Seismogram?"

Under "network", select the first two letters of your station code (from the REV page).  Scroll to the bottom, choose "Select Date", and click on April 6, the date of the Central Italy earthquake. 

A list of stations will come up.  Find your station, and look for three codes in a row that end in E, N, and Z.  (What do these letters indicate?) 

Choose "All Day".  Then click "Start Application".  It may take a few minutes; be patient.  When the three seismograms appear, look for evidence of the Central Italy quake.  "Zoom in" by dragging the yellow lines to the left and right to create a smaller "window"; then double-click the DMC button (the box under "Trace Access) to see the zoomed-in data.  You may have to try a few times; keep at it. 

Zoom in far enough that you can see the beginning of the P wave.  Read the time at which the P wave arrived (in yellow), and record it on the wiki page.
 
Third: Use the British Geological Survey seismogram data.   

Go to the Earth Science Department home page, then click "Terrific Links", then "Earthquake Watch", then "Seismogram Displays".  Click on the symbol on the United Kingdom on the world map .  Select one of the stations, and choose "Very Long Period".  Select April 6, 2009, and click "View". 

Find the Central Italy quake on this seismogram.  UTC time is on the right hand side.  Read these seismograms like you read lines in a book--from left to right, then continuing on the next line.  The different colors do not mean anything!  (They are there to help you see the lines more easily.) 

Finally: Send a group e-mail to me at L-Sanders [at] neiu.edu , giving your names, the station name, arrival times of the P and S waves, and the P-S lag.


n Calculate the speed of a P wave based on travel time and distance traveled.

n Using the data posted by the class last time on the wiki page, create three graphs and answer three questions about them. 

Graph 1: Show the travel time of the P waves from the Central Italy earthquake.  (This graph should look something like the graph from the Indian Ocean tsunami earthquake of Dec 26, 2004--but just for the P waves.)  Question: how does this graph compare to the Indian Ocean graph? 

Graph 2: Show the travel time of the S waves from the Central Italy earthquake.  (This graph should look something like the graph from the Indian Ocean tsunami earthquake of Dec 26, 2004--but just for the S waves.)  Question:  how does this graph compare to the Indian Ocean graph?

Graph 3: Show the distance to the Central Italy earthquake episode on the horizontal axis ("X" axis), and velocity of the P wave on the vertical axis ("Y" axis).  Question: is there a relationship between velocity of the earthquake wave and how fast the wave travels?  If so, describe and explain it.  

 

TOPOGRAPHIC MAPS

n Define:    ○ topography           ○ topographic map           ○ contour line

n Using the green globs of "playdough", sculpt a model of the hill outside the Science Building. 

n Scribe contour lines into your sculpture.

n Based on your model, sketch a topographic map of the area.

n Using a "green glob", create a model of a volcano (a mountain with a central crater at the top).  Scribe contours into the volcano at equal elevations, using a constant contour interval. 

n Draw the topographic map symbol used to indicate a closed depression, and explain why it is necessary to be able to have a separate symbol for this topography.

n Create a topographic model of a hill with a stream valley.

n Scribe elevation contours into the model.  Sketch a map of the hill and stream.

n Sketch and explain the relationship between contours and streams.

n Using the key/legend to USGS topographic quadrangles, interpret the symbols on a map.
 

FINDING TOPOGRAPHIC MAPS ONLINE AT THE USGS MAP LOCATOR WEBSITE *
(*for another option, try www.terraserver-usa.com; see the homework page for details)

You will need to be able to find USGS topographic maps for your next homework assignment.  They are posted online on several sites.  The Terraserver site is easy to use, and the USGS Map Locator site not much harder.  Terraserver is described on the homework page.  To use the USGS site, do the following:

1) Go to the Earth Science Department home page, click "Terrific Links!", and then click the USGS site (third row). 

2) Click "Maps, Imagery, and Publications", then, under "Maps", click "Download digital scans of topo maps". 

3) Click "Map Locator".  Using the map, zoom in on your site. 

4) Following the directions on the right hand side of the map, select "MARK POINTS ON THE MAP", and click on your point of interest.  A red bubble will appear. 

5) Click on the bubble, and a list of map options will appear.  Choose the first one on the list, and click "Download".  (These are big files, and may take awhile to download!) 

6) You will have to save the map somewhere (like to the Desktop, or "My Documents").  Be sure you know what the map's name is and where it is being saved.

7) When the download is complete, find the icon for the map, and double click it to open it.   
 
n Using a green glob, create the landform shown in the drawing on the poster sheet at the front of the room.

n Use the different scales on a topographic map to measure distances.

n Use a topographic map to estimate the latitude and longitude of a point.

n Explain what is meant by "7.5-minute quadrangle".
 
Using the topographic quadrangles provided, find at least one place that illustrates each of the following features.  Label and place a sticky note on one map or the other, to indicate the location of each feature.  It is necessary to find each feature only once.  
* a gentle slope
 
* a steep slope
 
* a closed depression
 
* a round hill top
 
* a ridge (elongated hilltop)
 
* a lake

* a benchmark		 * a stream; find two places where contour lines cross the same stream and put sticky notes on the map to show both places.  Tell what direction the stream is flowing.

* a “Gaging Station” along a stream
    
* a forested or undeveloped area (how can you tell?)

* an urban area (how can you tell?)
 

TOPOGRAPHIC MAPS and STREAMS

n Explain the meaning of the following terms: 

  stream               canal                        meander      oxbow (lake)                floodplain               
  watershed        drainage basin      divide            stream hydrograph    discharge

n Explain why not all streams have well-developed floodplains.

n Using the map of Major Watersheds of Illinois, determine what watersheds (more than one!) a particular Illinois town falls within.
 
n Find the following features on the topographic maps provided: 

           • two different well-developed stream floodplains: one should be the Mississippi River, and one should be another stream.  Measure their floodplain widths in miles.

• a meandering stream

• a channelized stream (or canal)

• a gaging station

• an oxbow and/or oxbow lake

• a stream that appears not to have a well-developed floodplain

• on the Clinton Illinois-Iowa map, find evidence of a former channel of the Mississippi River, now dry.

• a divide between two watersheds.  HINT:  Look for two good-sized streams, and then look for the topographically high area between them.  The Galena, Illinois map is a good one for this!

• the divide between the Lake Michigan and Mississippi River watersheds.  It appears on the River Forest Quadrangle.  It's not marked, so you'll have to use your knowledge of topographic maps to find the high area separating these two major bodies of water--Lake Michigan to the east, and the Des Plaines River/Illinois River/Mississippi River to the west.
 

Find stream records for last fall's flooding.  Follow the instructions that appear here.

n REVIEW: Explain the meaning of the following terms: 

      stream               canal                  meander                  oxbow (lake)               
      floodplain         watershed         drainage basin      divide 

 n REVIEW:  On a map of a meandering stream, show where erosion is most likely to occur, and where deposition is most likely to occur.          

n New this time: Explain the meaning of the following terms:  stream hydrograph         discharge       gage height

n Find stream records for last fall's flooding.  Follow the instructions that appear here.
 
          • Compare the stream hydrographs for the gaging stations along the Chicago River North Branch 
            OR        Compare the stream hydrographs for the gaging stations along the Des Plaines River. 

        • Compare the drainage areas of the various gaging stations.  What does this tell you about their "downstream order"?

        • Compare the gage datums (data!) of the various gaging stations.  What does this tell you about their "downstream order"?

        • Calculate the elevation of the water surface for each gaging station:

  Elevation of
the water		 = Gage
Height 		+ Datum of Gage

        • Find elevation of the water for the historical median, and also for the peak elevation during the flood.

        • Look at the topographic maps for each gaging station.  For each one, using the data from your table of values, estimate how high the water rose during the flood.  (This part is the hardest, mainly because of the need for detail on the maps.)

WEATHER FORECASTING

Examine the weather maps we have been collecting, and based on what you see there, answer the questions on the attached worksheet.

Explain the weather patterns you identified today, using the concepts of high and low pressure zones, warm and cold fronts, and precipitation, and wind directions.

Using the rules and patterns you identified, accurately forecast the weather based on the daily weather map.  In your forecast, consider wind direction, barometric pressure, precipitation, and temperature changes.
 

Department of Earth Science | Northeastern Illinois University

Copyright 2009 Laura L. Sanders.  Last updated April 28, 2009.