Velocity analysis using semblance |

Since its introduction by Taner and Koehler (1969), the semblance measure has been an indispensable tool for velocity analysis of seismic records. Conventional velocity analysis of seismic gathers scans different values of effective moveout velocity, computes semblance of flattened gathers and generates velocity spectra for later velocity picking (Yilmaz, 2000) .

While effective in most practical situations, semblance becomes troublesome in the case of strong variation of amplitudes along seismic events (Sarkar et al., 2001). A particular example is class II AVO anomalies (Rutherford and Williams, 1989) that cause seismic amplitudes to go through a polarity reversal. To address this problem, Ratcliffe and Adler (2000) and Sarkar et al. (2002,2001) developed algorithms for correcting the semblance measurement for amplitude variations.

In this paper, I interpret the semblance attribute as a correlation
with a constant and derive an explicit mathematical expression for the
measure which corresponds to correlation with an amplitude trend. This
measure is equivalent to *
semblance*
proposed by
Sarkar et al. (2002,2001). It reduces, in the case of
constant amplitudes, to the conventional semblance. I analyze the
statistics of the
semblance attribute and quantify the loss of
resolution associated with it. Numerical experiments with synthetic
and field data demonstrate the effectiveness of the
semblance as a
robust velocity analysis attribute, which is applicable even in the
presence of strong amplitude variations and polarity
reversals. Moreover, the ratio of the
and conventional semblances
serves as a useful AVO indicator attribute.

Velocity analysis using semblance |

2013-03-02