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Topography Can Affect Linearization in Tomographic Inversions

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Sean M. Wiggins, LeRoy M. Dorman, and Bruce D. Cornuelle

Scripps Institution of Oceanography, University of California, San Diego, La Jolla
LeRoy M. Dorman, Scripps Institution of Oceanography, UCSD,
9500 Gilman Drive, La Jolla, CA 92093-0215, USA.

ABSTRACT:
Linearized inverse techniques are commonly used to solve for velocity
models from traveltime data.
The amount models may change without violating
the linearity assumption is dependent on the surface topography and parameterization.
If, in a weak velocity gradient model, rays turn beneath a valley with
topography similar to the radius of curvature of the raypaths, then
large nonlinearities will result from small model perturbations.
Hills, conversely, create environments in which the data are more
linearly related to the models for the same model perturbation.
Simple, one layer, laterally homogeneous, constant
gradient models are used to study the effect of topography and parameterization
on the linearity of the
relationship between traveltime change and velocity model change.

##### Last Revised: 18 Apr 1996