Velocity-independent τ -p moveout in a horizontally-layered VTI medium a a Published in Geophysics, 76, no. 4, U45-U57, (2011) Lorenzo Casasanta and Sergey Fomel ABSTRACT Local slopes of seismic events carry complete information about the structure of the subsurface. This information is sufficient for accomplishing all time-domain imaging tasks, without the need to estimate or know the seismic velocity model. We develop a velocity-independent τ -p imaging approach to perform moveout cor- rection in horizontally-layered VTI media. The effective and interval anisotropic parameters turn into data attributes through the use of slopes and become di- rectly mappable to the zero-slope traveltime. The τ -p transform is the natural domain for anisotropy parameter estimation in layered media, because the phase velocity is given explicitly in terms of p. Therefore, the τ -p transform allows for reflection-traveltime modeling and inversion that are simpler than traditional methods based on Taylor-series expansions of traveltime in t-X domain. Syn- thetic and field data tests demonstrate the practical effectiveness of our method. INTRODUCTION macro model of the subsurface and remains one of the most labor-intensive and time- consuming procedures in the conventional approach to seismic data analysis (Yil- maz, 2000). In time-domain imaging, effective seismic velocities are picked from coherency scans. Moreover, anisotropic velocity model building requires more than just a single parameter scan for nonhyperbolic traveltime approximation (Alkhalifah and Tsvankin, 1995). This means that anisotropic velocity analysis is at least twice more computationally intensive than its traditional isotropic counterpart. Conven- tional human-aided velocity analysis takes up a significant part of the time needed to process seismic data. Even with semi-automatic picking software, this phase alone might take weeks or even months for modern 3D data sets. Several approaches have been proposed to automatize and simplify velocity analysis and traveltime picking procedures in order to reduce the time and manual work required for handpicked velocities (Lambar´ e, 2008; Lambar´ e et al., 2003; Siliqi et al., 2007). However, these tools still require significant manual inspection and editing for quality control. The idea of using local event slopes estimated from prestack seismic data goes back to the work of Rieber (1936) and Riabinkin (1957). Several following papers TCCS-1