Why Use Shear Waves?
Published:January 01, 1999
Even if most difficulties in using shear waves today have been significantly reduced, shear waves remain more difficult to operate than compressional waves, and often do not produce a better seismic image. Shear wave use has to be justified by bringing additional information. While some advantages to using shear waves have already been identified, we can expect further shear wave applications to be revealed as technology advances, particularly processing, amplitude preservation and imaging technologies.
In practice today, and in the following text, to use shear waves means to use shear and compressional waves together, even though the final shear wave image is the object of the exercise. This mainly occurs for practical reasons:
Acquiring shear waves most often means acquiring PS converted waves, thus additional recording of P waves is of marginal cost.
Even when the shear mode version is expected to be the best one, prior P wave processing of the same survey will greatly help shear mode processing.
The following situations and examples illustrate how shear waves can make an efficient contribution. These cases will be examined in more detail in Section 6 on interpretation.
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.”