1. Seismic Volume Visualization using VTK
Nicholas Schwarz
29 January 2004

2. Background
Seismologists study earthquakes.
Especially interested in P and S waves.
P waves are compressional/dilatational waves, i.e. the motion of any particle in the medium through which the wave goes is in the direction of the wave propagation.
S waves are shear waves, i.e. particle motion is perpendicular to the wave direction.

3. Problem
Visualize the seismic velocity in the Earth caused by earthquakes.
Show that waves propagate and reverberate from their origin around the surface of the Earth.

4. Previous Method
2D slices of the Earth at various latitudes.
Behavior we are interested in is not immediately apparent.

5. Better Method
3D volume visualization of the Earth.
Easier to notice pattern of propagation and reverberation.

6. Visualizing in VTK?
Where the data comes from, and how it’s formatted.
Representing data in VTK.
Mapping data for the display device.
Set properties (color, opacity, etc.).
Render.
Save rendered frames.
Create final animation (outside VTK).

7. Where does the data come from, and how is it formatted?
Generated from the van Keken, Tromp and Komatitsch Bolivia (1994) earthquake model.
Represents P waves only.
169 time-steps
Raw voxel data
Time-steps formatted as Bricks-of-Bytes (BoBs).
Each time-step in a separate file.
16-bit resolution

8. Representing data in VTK
Process one time-step at a time, and combine later.
Represented as image data because data is regularly structured voxels.

9. Mapping Data for Display Device
Software based ray-casting is designed for voxel data.

10. Properties

11. Properties
Colors assigned blue to red (lower magnitude to higher magnitude), heavily weighted toward more scalars associated with blue.
Opacity assigned to accentuate higher scalars.

12. Rendering

13. Save Rendered Frames

14. Create Final Animation
Can view animation as a flip book of separate frames, or create a movie in one of the standard formats (e.g. AVI, MPEG) using other software.

15. Bolivia (1994)