11 QUAL I TÉ GÉOPHYSIQUEAPPLIQUÉE Introduction 2 J.-L. Mari, C. Vergniault In the geophysics of oil exploration and reservoir studies, the seismic method is the most commonly used method to obtain a subsurface model. This method plays an increasingly important role in soil investigations for geotechnical, hydrogeological and site characterization studies regarding seismic hazard issues (Mari et al, 1999). The surface seismic method involves: • Seismic refraction (P or S waves), which provides a subsurface velocity model. This method, applied to P waves, is commonly used in the geotechnology field to identify changes in the position of the bedrock, as well as longitudinal changes of its physical state or that of its overburden (see AGAP’s Guide Sismique réfraction, O. Magnin, Y. Bertrand, 2005). • Seismic reflection, a type of two or three-dimensional subsurface ultrasound method, which initially provides an image of the acoustic impedance contrasts of the subsurface. Depending on the means implemented, an investigation can reach hundreds of meters to several thousand meters in depth. However, the method does not perform well in the first 20 to 50 meters. This chapter of Well seismic surveying and acoustic logging is published under Open Source Creative Commons License CC-BY-NC-ND allowing non-commercial use, distribution, reproduction of the text, via any medium, provided the source is cited. © EDP Sciences, 2018 DOI: 10.1051/978-2-7598-2263-8.c002
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