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Abstract:
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In seismic exploration, knowledge and understanding of the near surface is paramount for recovering reflectors with a high bandwidth, and uncontaminated by shallow subsurface effects such as strong statics, surface waves and scattered noise. High quality multicomponent seismic data are obtained using a vertical and two orthogonal shear-wave vibrators as seismic sources, and recorded by three-component (3-C) geophones in a two-dimensional (2-D) acquisition geometry. The vertical vibrator is predominantly a compressional wave (P-wave) source, while the inline and crossline shear-wave vibrators are predominantly SV- and SH-wave sources, respectively. Surface wave dispersion curves (Rayleigh wave and Love wave) can be interpreted from phase-velocity measurements taken from the appropriate source-receiver components, and 1-D shear wave velocity profiles derived through linearized inversion. Without a priori knowledge of the velocity distribution with depth, the inverted profiles often result in unrealistic models. A simple model with relatively few parameters to solve for then constitutes the target of the inversion. An important aspect of our work is validation of the inverted shear-wave velocity profiles using multicomponent elastic forward modeling. Inversion and modeling tests show that a relatively simple shallow profile explains the observed surface-wave phase-velocity measurements. Our results indicate that use of additional information such as reflection, refraction and borehole data are needed to more accurately invert for the shallow subsurface.
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