Third-party Add-ons

 

A good number of third-party add-ons have been created for ArcGIS to address a number of problems. Go to http://www.esri.com and then click on the Support tab. Now click the Downloads tab and select Scripts. Choose ArcGIS Desktop and then type “profile” in the search box and run a search – then click on EZ Profiler for ArcMap 9.x(Multi-layers & profile lines version) – your may not be able to download this file in class, but you see how the process works. The file is included in your download file below. Unzip it – you will find a .dll file (profile91.dll) which will automatically create a new tool bar when loaded into ArcGIS. To load, go to Tools > Customize and Add from file. You then simply active the new tool in the Customize list.

This tool is now ready to use.

Problem

 

Possible new terms:

 

  1. Graben – a valley that is down-dropped, due to extensional tectonics, and is bounded on both sides by normal faults.
  2. Horst – a block that is up-thrown, relative to grabens, that is bounded on both sides by graben bounding normal faults. 
  3. Nick point – a change in stream gradient that can be caused by an earthquake or by a change in rock type or competence.

 

 

In this lab you will build on skills you have already learned, learn how to use third-party add-on software, and use the 3-D analyst. You will also solver a problem in tectonic geomorphology by mapping tectonic signals of historical earthquakes.

 

 

Here is the problem: A graben has formed between a mountain rage and some hills about 2.6 kilometers to the west. The graben is bounded by a west-dipping normal range-front fault on the east. It is bounded by a east-dipping normal fault on the west. The hills are a horst that is bounded by the previously mentioned (western graben bounding fault) on the east and a west-dipping normal fault on the west, which has taken up the energy that once activated the range-front fault which is now virtually inactive (Fig. 1a & 1b)

 

 

Figure 1. Developing fault system related to extensional pull-apart (extensional duplex). The old range front fault is becoming less active as the new major range-front fault has stepped to the west. The entire block consisting of the Hills, central graben, and mountain range is moving east in relation to the western graben. 

 

The hills are capped with alluvium that is late Tertiary in age (Pliocene ~3 to 5 Ma?). The central graben has deposits of both Quaternary (recent) alluvium and older alluvium that could represent early deposition as the graben first began to down-drop towards the end of the Pliocene epoch and into the Pleistocene. Through this time, multiple earthquakes created several displacements which are recorded as nick points in the bedrock of channels. These nick points can be found using 10 m spatial resolution digital elevation models.  

 

Your job is to find the maximum number of earthquakes that have occurred and the first earthquake that began the development of the central graben. The stream gradient upstream from this nick point should, if projected westward, nearly intersect the top of the Pliocene alluvium capped hills (a couple of million years of erosion will make the projected line pass just over the hills). This projected line will act as a surrogate for a paleosurface. This distance from the paleosurface to the valley floor will give an estimate of the distance the valley has down-dropped.

 

Determine:

 

  1. How may earthquakes have occurred?
  2. How far has the valley down-dropped on its eastern and western margins and in the middle?

 

 

 

Figure 1b – Image of study area with features.

 

INSTRUCTIONS

 

First, we will create a 3-D view to become familiar with the landscape.

 

  1. Download data here.

 

  1. Open ArcGIS and load all data into table of contents.

 

  1. Create a shaded relief map from the DEM

 

  1. Open ArcScene – in ArcCatalog to Tools > Extensions and activate 3D Analyst. Then go to Tools > Customize and activate 3D View Tools. The 3D View tool bar should now appear (Fig. 3). Click the highlighted button on the right side.

 

 

Figure 3 – 3D View Toolbar.

 

  1. Use ArcCatalog to place the Brovey, DEM, and Hillshade images in the ArcScene table of contents.

 

  1. Drag the hillshade image to the top of the ArcScene table of contents and right click it to bring up the context menu.

 

  1. Click Properties and select the Base Heights tab. Select Obtain heights from layer surface and change the input to dem. As the dem dataset is in XYZ meters, there is no need to make a Z conversion. Click on OK.

 

  1. No go to the View pull-down menu and select Scene Properties. Change the vertical exaggeration to 2. Click OK.

 

  1. You can also put the brovey_521 image at the top of the table of contents and make it appear in a 3D perspective. Give it a try.

 

The 3D images are used to help you visualize topography. Keep ArcScene open but minimize it as necessary to work in ArcGIS.

 

Taking Channel Profiles

 

You will now be guided, in class, through some options to solve problems stated above. You are also encouraged to pursue your own methodology and work with others in the class on ideas. To begin with, use the profile tool to digitize up several stream channels in the mountain range east of the central graben. Look at the profiles that are created. Do you see any nick points?

 

Turn in a one or two page report on your methodology, how many earthquakes may have occurred, how you determined the how much the central graben has down-dropped, and the problems that you see using ArcGIS and the Profiler tool as well as suggestions for improvement.