Wavepath eikonal traveltime inversion: theory

The paper presents a general formula for the back projection of traveltime residuals in traveltime tomography. For special choices of an arbitrary weighting factor this formula reduces to the asymptotic back-projection term in ray-tracing tomography (RT), the Woodward-Rocca method, wavepath eikonal traveltime inversion (WET), and wave-equation traveltime inversion (WT). This unification provides for an understanding of the differences and similarities among these traveltime tomography methods. The special case of the WET formula leads to a computationally efficient inversion scheme in the space-time domain that is, in principle, almost as effective as WT inversion yet is an order of magnitude faster. -from Authors