A Deep Field Trip Exercise

 SO461 Lab, Fall 2008

Due: Tues, 9/16 during the lab.

This lab is entirely individual effort.

You are to prepare a report on the tectonic features of the deep region, with diagrams showing how the faults are related to topography in the area.  You can cut and paste any of the graphics from the screen into Word.  You should aim for the equivalent of at least 1-2 pages of text double spaced.  You should answer the questions below, but should consider this a writing exercise and include your answers into a good, well-organized discussion of what  you see, and not just a simple answer to the set of questions.  You should contrast this with the Afar area.

You will put references to the sources of the data sets in your report, in the correct format from the department style manual.

The help file for MICRODEM (30 MB download at http://www.usna.edu/Users/oceano/pguth/microdem/win32/microdem.chm) explains how the program works, and has some suggestions on how to use it for looking at fault scarps in topography.  You want to start at the structural geology page, under program versions, in the table of contents.

We have several data sets:

• ETOPO5
• The Smith & Sandwell predicted bathymetry, at http://topex.ucsd.edu/marine_topo/mar_topo.html which will put this area into global context and show you the big picture. If you want to cite this data source, you should use the paper from Science that is noted on the web site.
• A file with multibeam bathymetry, c:\mapdata\adeep_field_trip\adeep_field_trip.dem.  This has 200 m spacing, so it shows less detail than we saw in Afar.  Multibeam bathymetry merged from two data files at http://ocean-ridge.ldeo.columbia.edu/general/html/home.html
• Earthquake focal mechanism data from http://www.globalcmt.org/CMTsearch.html 

Geology terms:

• Horst: an upthrown block, with normal faults on either side.
• Graben: a downthrown valley, with normal faults on either side.  Also called a rift valley when it has a specific plate tectonic setting.

We will use a modified version of Prof Guth's MICRODEM program. 

• Use the leftmost button ("Open project") and pick the DeepFieldTrip.MSC, or use the fourth button from the left ("Open DEM") and pick the deep field trip DEM. 
• The initial views show you the entire data set, at reduced resolution.  You can zoom in  to see greater details.  In particular you will want to do this as you start looking at the individual faults.
• You can use the Prof and OpenGL buttons to get different 3D and 2D views of the terrain.  The views will probably have a default vertical exaggeration, which you should consider when you are trying to visualize the topography.

Questions to consider:

• What types of faults are located in this area?  Do the strikes of the faults correlate with any topographic features?  Do the dips?  Can you suggest whether one of the focal planes is more likely the fault plane?  What does this suggest about the plate tectonic setting of this region?
• Are the ridges steeper on one side, or are they symmetrical?  Does this relate in any way to the faults?
• Is the multibeam bathymetry better than Smith & Sandwell's for performing this analysis?

This is the middle of the ocean, and these are small earthquakes.  The locations may not be perfectly accurate, so look in the vicinity when drawing conclusions.

Running this lab at home:

1.  You need to download MICRODEM from http://www.usna.edu/Users/oceano/pguth/microdem/win32/microdem_setup.exe and you should get it after 1/23/2006 for best operation.  After you install the program, you probably want to replace the excutable program file with the newer version at http://www.usna.edu/Users/oceano/pguth/microdem/win32/microdem.exe 

2.  You need to get the data files at  www.usna.edu/Users/oceano/pguth/website/so461web/mapdata/adeep_field_trip/adeep_field_trip.DEM .  The DEM file should be placed in c:\mapdata\dems, and the earthquake file must be placed in c:\mapdata\database

3.  If you want a small scale map showing a large region around this area, get the ETOPO5 DEM at http://www.usna.edu/Users/oceano/pguth/microdem/data/ETOPO5.zip  and should place it in  c:\mapdata\dems.  To get the earthquakes to plot on this map, you will need to go to the Options menu option, go to the Import/Export tab, and uncheck the Wrap ETOPO5 check box.