Shear Wave Acquisition
Published:January 01, 1999
Designing a pure compressional source in elastic media is not an easy task, even in laboratory conditions—in practice marine seismic corresponds to the only situation where pure P wave sources are operated. Once a so-called P source is coupled withe an elastic material, any difference between the actual environment and a perfect spherical symmetry generates shear stresses, thus shear waves. For example, SH waves have been observed from explosions near the boundary of two media that present large impedance contrasts (Shtivelman, 1978).
A similar problem appears for designing shear sources, which should be seen as sources emitting preferably shear waves, or, in other words, minimizing the P wave emission. An additional problem with shear sources appears with coupling, as shear modes may cause lateral sliding, while compression does not.
Figures & Tables
Shear Waves from Acquisition to Interpretation
“This book, produced for use with the third SEG/EAGE Distinguished Instructor Short Course, addresses the practical aspects of multicomponent data acquisition, processing, and interpretation. The first part of the book is devoted to overcoming the difficulties associated with shear-wave acquisition. Converted-mode operation is covered in detail using real-life examples. The particularities of sea-bottom receivers also are examined. The second part reviews the processing and the main challenges of the shear-converted modes: static corrections, gathering, velocity analysis, and compensation for shear-wave splitting in axial anisotropy. The book gives a detailed description of processing sequences, and 2D and 3D results, yielding natural axis orientation of layers, are compared in shear and PS converted modes. The third part is devoted to case histories in which new attributes, such as VP/VS ratio, crack density, or fracture orientation, are illustrated in a reservoircharacterization context. These case histories can guide the geophysicist to decide if a particular geologic situation can be handled best using shear waves.”