Offset Selective Dispersion Imaging

A 2-D wavefield transformation method commonly used to image dispersion patterns of surface waves recorded from a multichannel survey applies the summation of wavefields over the entire offset range covered by the input record to take a full advantage of the widest spatial bandwidth ever possible. In reality, however, this full-offset summation may not always be the best choice because the prevalent offset range for a particular mode may be confined within a certain fraction of the full range and other mode(s) that may prevail in the remainder of the offsets may hinder the effectiveness of the summation. A simple modification can be added to an existing transformation scheme in such a way that minimum and maximum offsets are determined as certain ratios (for example, 0.1 and 5.0) of the wavelength of the mode being calculated. If these ratios are properly chosen, the modification can improve the imaging resolution and this usually leads to an enhanced delineation of multi-modal dispersion characteristics, which is one of the critical factors contributing to an increased accuracy during the inversion. Both syntheticand field-data sets are used to demonstrate the effectiveness of the offset-selective imaging.