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Downward-continuation methods are very sensitive to velocity models (Berkhout, 1982; Yilmaz and Chambers, 1984; Claerbout, 1985; Al-Yahya, 1989; Deregowski, 1990; Liu and Bleistein, 1994; Varela et al., 1998). Using inaccurate velocity models in these methods can generate low quality images. Their sensitivity to velocity errors, however, makes them a good tool for velocity analysis. Using migration methods for estimating velocities is generally known as migration velocity analysis (MVA). Migration velocity analysis consists of the domain in which it is carried out, and the inversion scheme used to update the velocity model. There are different domains and inversions schemes for MVA. In this paper, some well known domains for migration velocity analysis will be presented and linked to each other. These domains include residual curvature analysis (RCA, Al-Yahya, 1989), depth focusing analysis (DFA, Faye and Jeannot, 1986), and the common focus point (CFP, Berkhout, 1997.a) analysis. Presenting them using the same migration method, shot profile migration, makes them easier to understand and compare. I then show how different aspects of the RCA, DFA, and CFP methods can be combined into a unified domain for migration velocity analysis. I will call this approach the common image cube analysis (CICA). Instead of just taking the zero-lag cross-correlation at each depth level as in RCA, all the cross-correlation lags are stored. The result is a cube that contains more prestack information than the other methods. This cube was first mentioned by Faye and Jeannot (1986). More recently, different slices of this cube were shown by Wang et al. (2005) to relate focusing errors to velocity updates using tomography. The CFP approach offers more prestack information than the RCA and DFA approaches, but less prestack information than the CICA approach. Since the RCA, DFA, and CFP approaches have been shown by numerous authors (see e.g. Al-Yahya, 1989; Faye and Jeannot, 1986; Berkhout, 1997b; Berkhout, 2001) as appropriate domains for MVA, the CICA is also expected to do so, since it is just the integration of different aspects of these methods. In fact, the traveltime tomography that is currently used in CFP (Cox, 2001; Thorbecke, 1997; Berkhout, 1997b; Berkhout, 2001) can be used in CICA to update the velocity model. The CICA is a promising tool for MVA, but requires developing some software in order to compare it with other approaches. |
