A multicomponent offset VSP scale model investigation

The key to obtaining improved knowledge of the subsurface seismic structure lies in the use of multicomponent recording (multi-directional sources and triaxial detection) and vector (elastic) wavefield imaging. To this end we have assembled a two-dimensional, biaxial physical seismic model system.

The laboratory facility has been used to acquire vector seismic data over a very simple reflecting structure for both VSP and MSP (inverted VSP) array configurations. Controlled direction reception (CDR) filtering of the data yields four sections for interpretation: upgoing P, downgoing P, upgoing S and downgoing S.

The model experiment has revealed an interesting mode conversion from Rayleigh wave (or tube wave, when extended to the field situation) to scattered S wave, which dominates the seismic section. This wave could be a troublesome form of noise on scalar seismograms, but it can be eliminated by means of CDR to pass the P waves only. Alternatively, it can be viewed as a useful multicomponent diagnostic for detecting fractures or other impedance boundaries intersecting the borehole.