Fig. 5.

(a), (c) Absolute value of the axial displacements in frequency domain and (b), (d) displacements in the time domain for a three-layered medium, where Young’s modulus of the second layer (E₂) is varied from 5 kPa to 50 kPa. Shear viscosity is (a–b) 0.1 Pa s ( ${\mu }_2^1={\mu }_2^2={\mu }_2^3=0.1$ Pa s); and (c–d) 1 Pa s ( ${\mu }_2^1={\mu }_2^2={\mu }_2^3=1.0$ Pa s) for all layers. Other parameters are: E₁ = E₃ = 10 kPa, h₁ = 3 mm, h₂ = 6 mm, H = 10 mm. The case E₂ =10 kPa corresponds to a homogeneous medium. In the time domain solution the time of excitation is 5 ms.