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Table of Contents for GEON IDV web site Introducing the GEON IDV GEON IDV Displays, and Data from UNAVCO and GEON Download & Run the GEON IDV Tutorial ... How to Use the GEON IDV ... More Tips Data Formats: How to Put Your Data in the IDV

GEON IDV Tutorial

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Part 4 - Exploring Seismic Tomography Data with the IDV, and Seismic Anisotropy plots

We will  make several displays from a seismic tomography 3D grid of Vp perturbations, i.e. the data source 
"Seismic tomography / Yellowstone ..." as follows. 

First hide the earthquake locations, focal mechanisms, GPS vectors, and 3d topography you made, by checking off the boxes to 
the left of the each display's name in the main window Displays list.

To connect to the 3D grid of tomography results, in the Dashboard's "Field Selector" window:
click on the data source file "Seismic tomography / Yellowstone ..." item loaded from the UNAVCO catalog.  
"shear velocity perturbation in Yellowstone" should appear in the "Fields" panel.  
(it's really P wave velocity; the data file has an error in the metadata.) 

In the Dashboard's "Displays" panel click on the blue "3D Surface" button, and then click "Isosurface" under that.
Click on the "Create Display" button below. A big green blob should appear in the display. This is the 3D surface of 
one Vp value; the average value of all Vp perturbation values in the grid.

To change the data value of the surface, in the Dashboard you now see the display control for the display just made. Change the 
isosurface value to negative 2.2. 
(You can use either the entry box or the slider that pops up from the tiny slider icon).  
The color and shape of the isosurface both change.

In this data set, the data units are percent, so you now see the regions that are  2.2 % slower than
the reference velocity in the area - a dual low velocity zone below the most active part of Yellowstone National Park. Rotate the
view by dragging the mouse to see the feature. 

When the view is exactly from the side, the mouse pointer shows the depth readout in the lower border.
The top is near -3.2 km and the bottom near -12.2 km. (In this data set the top of the data is at -3 km.)

To make a Plan View (horizontal cross section) of the same data, in the Dashboard's Displays panel click on "Plan View -> Color image"
and click "Create Display."  A colored-by-value image appears in the display. You can change its level (altitude) in the Display control, with the
"Levels:" choice. Set -6 and the plan view bisects the isurface. You can also make contours in a plan view.

To make a vertical cross section, in the Dashboard's Displays panel click on the "Cross sections" blue button, then click 
"Color-shaded Vertical Cross Section," 
and click "Create Display." The vertical cross section appears in both the main 3D display and in the display control window as well.

In the main display the vertical cross section display has a control line across the top of the wire frame box.
Mouse-drag  the control pointis at either end of the line, or in the middle, to position and angle the
cross section any way you like. The middle point drags the line at the same orientation; the end point controls change the
location of that one end point.

Vertical cross sections may be contoured.

You can also make a vertical probe or profile of 3D tomography data (in Dashboard's Displays panel, click on blue Probes button, then
on Vertical Profile. The profile's location is a line in the 3D display; the values are plotted in the display control. Drag the
control point on top of the vertical line in the 3D display to change the profile location.

       

There is also a "display" to let you sample the values anywhere inside a 3D grid, the "Data Probe."
Using it requires careful use of setting points of view of the display (sideways and overhead both)
to exactly position the mouse pointer in 3D.

You are now ready to explore and use the IDV. You have seen only a little of its power. For a solid grounding read the most common GEON IDV questions and answers in our How to Use the GEON IDV web page.

To see really complete use of the GEON IDV's capabilities in exploring regional geophysics,
see GEON IDV Displays of Yellowstone Park Geophysics

Yellowstone area GPS, transparent 3D topography relief, caldera outline, seismic tomography model, faults, and focal mechanisms.
Data provided by Bob Smith, Univ. Utah, et al. View is oblique from WNW.

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Seismic Anisotropy

If you do not use seismic anisotropy data, you can go on to the next part of the tutorial.

In the "GEON IDV - Map Display" window, do menu choice Edit->Remove all Displays. Then do menu choice Projections->Set->U.S.->Southwestern U.S.

To connect to an example of anisotropy data, in  the Dashboard window, click the tab "Data Chooser," then click the "URLs" tab.
Enter http://geon.unavco.org/unavco/anisotropy/Waite_WesternUS_anisotropy.nc
in the "URL" entry box and hit Add Source or the enter/return key.

In the Fields Selector that opens, click Create Display (the Displays panel should show Point Data -> Point Data Plot).

The initial plot of the seismic anisotropy data shows station locattions with blue crosses. In it's display control in the
Dashboard, choose Station Model: Seismic wave polarization. A plot like the one below appears.

Average station anisotropy observations compiled by G Waite.

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