# Dictionary:Semblance

(sem’ bl∂nz) A measure of multichannel coherence. If is the sample of the trace, then the semblance coefficient is

where channels are summed; the coefficient is evaluated for a window of width centered at . It is basically the energy of the stack normalized by the mean energy of the components of the stack. This is equivalent to the zero-lag value of the unnormalized autocorrelation of the sum trace divided by the mean of the zero-lag values of the autocorrelations of the component traces. Perfect agreement yields a value of unity.