Afar Field Trip Exercise

SO461 Lab, Fall 2008

This exercise is entirely individual effort.  It will be due at the start of  lab Tuesday 9 Sept 2008.

You are to prepare a report on the tectonic features of the Afar region, with diagrams showing how the faults are related to topography in the area.  You are to clearly describe the important characteristics of the earthquakes and faults, and relate them to larger geologic features and processes.

• Describe the strike and dip of the faults.
• Describe the orientation of ridges.
• Show profiles across at least two representative faults.

You can cut and paste any of the graphics from the screen into Word, and 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.

Afar was the home of  Lucy, Australopithecus afarensis.

The help file for MICRODEM (35 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 four data sets:

• Shuttle Radar Topography Mission (SRTM) digital elevations.  These were recorded about every 30 m for military use, and about every 90 m for civilian use, which is the version we have. The default display will be shaded relief; you can switch to elevation mode, or add elevation coloring to the shaded relief, by right clicking on the map and selecting "Display parameters".
• Landsat Thematic Mapper Imagery in 6 spectral bands (visible and infrared), at 30 m resolution.  By default this will display as a false color composite; the red is really infrared, and strong infrared reflections indicate vegetation (what little there is here).
• Landsat Thematic Mapper Imagery in 1 panchromatic band (visible) at 15 m resolution.
• Earthquake focal mechanism data from Harvard University.

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

• Open MICRODEM, and then pick the Options menu choice and pick the "Structural Geology" menu choices.  This removes many options in the program that you will not want.
• Use the leftmost button ("Open Project") and pick the Afar field trip project.  This will open the TM imagery and the SRTM DEM.
• Open the focal mechanism database with the last button on the right.
• The initial views show you the entire data set, at reduced resolution.  You can zoom in on all maps to see greater details.  In particular you will want to do this as you start looking at the individual faults.
• You can use the LOS and OpenGL buttons to get different 3D and 2D views of the terrain.  OpenGL can place the satellite imagery on top of the topography.  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?
• What is the large feature located at about N11°17',   E 41°38'?  What is its size and steepness?  Does its presence fit with the faults you can see?

Metadata on the data sets:

• 3" SRTM data from USGS, merged and holes filled with SRTM30.  Reprojected to 50 m UTM DEM with decimeter resolution.
• Landsat ETM+ downloaded from University of Maryland, and subset.
• Focal mechanisms downloaded from Harvard, and converted into a dBase table.

Download MICRODEM to your computer and install it.

Data for this lab is available.  It is a 78 MB ZIP file, which you must place in c:\ and then unzip.  This will put the data files in the correct locations on your hard disk.  You must be careful that Windows does not put the files into c:\mapdata\mapdata, in which case you must manually move them.  If the unloading is correct, you will have a "c:\mapdata\afar_field_trip" directory.

Alternate data set: Corinth.DEM

Reference: paper by Waltham, 2005, in Geology Today.