81 2. Surface geophysical methods original state after the causes of deformation have disappeared, i.e. when the medium has not been damaged by the wave passing through it. 4. A receiver spread. It is capable to record the deformations generated by the source after propagation in the geological medium: • either by variations in the displacement, velocity, or acceleration of particles (geophones, accelerometers), • or by pressure variations (hydrophones). (a) (b) Figure 2.19 Seismic wave propagation. (a) Snell’s law, after Lavergne (1986), (b) the various types of seismic surveying versus critical angle.
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