Computer Aided Tomography

Tomos: cut (Gr.)

Extensively used to find 3D structure from surface measurements (X-ray, sound, seismic waves)

Principles of tomography

Seismic tomography

• Earthquake source & receivers

• 3D perturbation vs 1D Earth model (PREM)

• Difficulties:– Curved raypaths that depend on velocity– Poor distribution of earthquakes and receivers– Lack of high precision in earthquake source and

time.

Mantle tomography

• E.g., Bijwaard, Spakman, Engdahl, 1999.

Subducting Farallonslab

Caveats

• Low resolution

• Variable resolution

• Artifacts of inversion & smoothing

• Choice of 1D reference model