Fifty years of seismic anisotropy studies in Russia

This is a historic overview of seismic anisotropy studies in Russia run as part of seismic exploration work in the 1940s through the 1980s, with a focus on main research lines. At the early stage in the 1940s through 1950s, most important contributions belonged to A.G. Tarkhov, Yu.V. Risnichenko, and S.M. Rytov (averaging the parameters of stratified media), I.I. Gurvich (processing reflection and refraction traveltime curves in media with elliptical anisotropy), and N.I. Berdennikova (shear-wave velocity anisotropy). In the 1960s–1980s, there were two basic schools of thought: one of G.I. Petrashen’, with a more theoretical approach, and the other of N.N. Puzyrev dealing more with experimental work. Most of experiments addressed a newly discovered phenomenon of azimuthal anisotropy. This anisotropy appearing as “anomalous” polarization of shear and converted waves was found out to result from vertical fractures in rocks. The unusual polarization became understood owing to Klem-Musatov’s model of a subsurface with a system of aligned cracks. The problem was fully resolved after field data had been processed with an algorithm by I.R. Obolentseva and S.B. Gorshkalev, for separating the total field of interfering shear waves of two types into fast and slow phases polarized in crack-parallel and crack-orthogonal directions, respectively.