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Summary Triplication of a wavefront, also classically known as birefringence, can and does occur in transversely isotropic (TI) media. With the growing interest in shear waves, and in particular, converted shear waves, it becomes necessary to study this phenomenon, and the bright spots that accompany it. In a plane that includes the medium’s rotational symmetry axis, there may exist a range of angles within which the qSV wave, whose polarization lies in that plane, may propagate at three distinct velocities. The region of the qSV wave curve where this can occur always corresponds to the region of the qSV slowness curve where the closed qSV curve about the origin is concave. When the range of angles is small and the three arrivals are close together, the usual situation, the qSV wave within that small range will be significantly brighter than in other directions.
- Geophysics > Seismic Surveying (1.00)
- Geophysics > Borehole Geophysics (0.87)
Summary The borehole orbital vibrator source (OVS) has many unique properties that are useful for cross-well, single-well, and borehole-to-surface imaging of both P-(compressional) and S- (shear) wave velocities of reservoir rocks. In this paper, we present an analytical source model for OVS in the frequency-wavenumber domain. Using this model, the characteristics of the body waves around the borehole and borehole-guided waves generated by a variety of vibrator motions is examined. To explain large tube wave amplitudes observed during field measurements, we also examine the effect of misalignment between OVS and the borehole axis on the generation of tube waves using the analytical model.