Quality control of picks

The easy way to QC picks is to align the data on a constant time line using the picks in the headers for static shifts. The program, bshf, will do this. For example, type the command 

bshf twave.seg 0 1 .02 

This will align the data on the .02 second timing line by applying static shifts equal to the negative of the pick value. Figure 18 shows this process (picking, insertion to headers, and alignment in time for QC) at the final alignment step. If a pick were bad, it would be evident by a misalignment of the corresponding trace, relative to its neighbors. In Figure 18, all the picks look good.

Figure 18: Alignment T-component data by first break picks for QC

It is evident that the propagating wavelet is changing shape (first motion peak stretches in time with increasing distance from the source). Such wavelet stretch may be interpreted as inelastic wave propagation, perhaps consistent with a viscoelastic, Kelvin-Voigt, constitutive model. Despite the expected velocity dispersion, one can determine a group velocity for the frequencies which dominate the amplitude spectrum of the signal.