GDS has been processing three-component seismic data from a variety of geographic areas and has developed software tools for 2D pre-stack migration and velocity analysis for pure and converted waves using the Kirchhoff integral. We have developed a software module that supports stack scaling in the time domain and evaluation of spectral composition within the given interval in order to evaluate the Vp and Vs velocity ratio. 

The main known challenges (unlike in P-wave processing) are associated with asymmetrical incident and upgoing wave paths, variations in the depth of the conversion point and statics correction for converted waves.

Residual receiver point statics is another important issue in X-component processing. The interactive statics correction approach implemented in the GDS's IST-3MP software suite that is widely used for reflected wave processing also allows us to account for near-surface anomalies affecting the radial component of the converted wave. Our pre-stack migration software supports three incident and upgoing wave time calculation methods based on selected velocity models:

• Average velocity time migration
• Interval depth migration based on a grid-based velocity model
• Interval depth migration based on a grid-based velocity model, accounting for refraction at selected boundaries

The depth-velocity modeling consists of the determination of average or interval velocities using our vertical or interval migration velocity software. The software generates migrated data sets and average or interval velocity spectra (user selectable) to be used in optimization of the V (x) velocity graph. In case of interval-by-interval analysis, the software also lets us refine the interval geometry. If interval velocities are calculated, the processing takes place in a sequence, going from the upper boundary to the lower, and velocities along the selected interval are evaluated taking into account velocity distributions and boundary geometry of overlaying intervals. The procedure is subdivided into two steps. First, the incident wave velocity is determined from pure wave records. Then, the upgoing wave velocity is evaluated in a similar manner using the converted wave CSP records as inputs and taking into account the incident wave velocity.

Use of the the pre-stack migration algorithm for incident and upgoing waves ensures accurate imaging.

We have developed a unique set of software tools implementing methods of interactive migration velocity analysis for various wave types, which allows us to combine refraction and conversion data for various waves to better delineate structural features.

Vertical migration velocity analysis Horizontal migration velocity analysis Pre-stack depth migration