Abstract. Accurate subsurface velocity models are crucial for
geological interpretations based on seismic depth images. Seismic reflection
tomography is an effective iterative method to update and refine a
preliminary velocity model for depth imaging. Based on residual move-out
analysis of reflectors in common image point gathers, an update of the
velocity is estimated by a ray-based tomography. To stabilize the
tomography, several preconditioning strategies exist. Most critical is the
estimation of the depth error to account for the residual move-out of the
reflector in the common image point gathers. Because the depth errors for
many closely spaced image gathers must be picked, manual picking is
extremely time-consuming, human biased, and not reproducible. Data-driven
picking algorithms based on coherence or semblance analysis are widely used
for hyperbolic or linear events. However, for complex-shaped depth events,
purely data-driven picking is difficult. To overcome this, the warping method
named non-rigid matching is used to estimate a depth error displacement
field. Warping is used, for example, to merge photographic images or to match two
seismic images from time-lapse data. By matching a common image point gather
against its duplicate that has been shifted by one offset position, a
locally smooth-shaped displacement field is calculated for each data sample
by gather matching. Depending on the complexity of the subsurface, sample
tracking through the displacement field along predefined horizons or on a
simple regular grid yields discrete depth error values for the tomography.
The application to a multi-channel seismic line across the Sunda subduction
zone offshore Lombok island, Indonesia, illustrates the approach and
documents the advantages of the method to estimate a detailed velocity
structure in a complex tectonic regime. By incorporating the warping scheme
into the reflection tomography, we demonstrate an increase in the velocity
resolution and precision by improving the data-driven accuracy of depth
error picks with arbitrary shapes. This approach offers the possibility to
use the full capacities of tomography and further leads to more accurate
interpretations of complex geological structures.