“…Sari and Salk (2002) proposed hyperbolic variation in density with distance. Recently, Kakar and Kakar (2016a, 2016b) discussed the effects of various factors, such as homogeneity, heterogeneity, initial stresses, internal friction and nonhomogeneity, on the propagation of the torsional surface wave in elastic and viscoelastic layers. Likewise, different authors have proposed different forms of density and rigidity variation with depth, such as linear, quadratic, harmonic, hyperbolic and so on, to study wave propagation inside the Earth.…”