| Summary: | The nature of geoacoustic waves is discussed, based on comparison of the results of seismic and acoustic studies in the Fennoscandian Shield with the drilling record of the Kola Superdeep Borehole: 12262 m (1970-1990), Russia; Gravberg 6337 m (1986-1987), Sweden; Outokumpu - 2516 m (2004-2005), Finland; Pogranichnaya - 5200 m (2004-2006), Russia; Onezhskaya - 3537 m (2007-2009), Russia. The assumption that the crystalline crust has a heterogeneous structure with gradient variations and elastic wave velocity inversions and the vertically and laterally varying degree of differentiation is wellbased. The nature of seismic boundaries depends on differences in rock composition and the physical state of the rocks. The results of geophysical studies, conducted during deep drilling in the Fennoscandian Shield, make investigators reinterpret the geological and geophysical data.
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