f The Feasibility Of Shear Wave Reflection Profiling Of A Shallow Bedrock Surface Buried Under Alluvium

A number of papers have been written in the last few years<br>concerning optimum techniques for adapting classical reflection<br>techniques to the shallow environment. However, despite an overall<br>successful evolution of shallow applications, two basic problems have<br>hindered the implementation in some geologic environments. One<br>problem has been the overwhelming of the weak reflection by the<br>multi-mode Rayleigh ground roll propagating along the free surface.<br>Another is that the water table forms such a great impedance<br>contrast that it is often difficult to illuminate reflectors below it.<br>Both of these problems are particularly bothersome when the<br>subsurface to be investigated involves the sequence dry<br>alluvium/wet alluvium/bedrock. The use of shear wave profiling<br>offers a possible solution to these problems. Love waves do not exist<br>on the free surface of a half-space, and if the thickness of the<br>alluvium is several times the wavelength of the Love wave, the<br>development of the shear “ground roll”. will be inhibited. Also, shear<br>waves are not sensitive to changes in type of pore fluid and do not<br>“see” the water table. Thus, we might expect to be able to propagate<br>shear energy through the water table and obtain reflections from<br>below it even though compressional waves cannot effectively<br>penetrate the air/water interface.