1. Observation methods were considered in a paper, delivered by E.I. Gal'perin, which was written by a group of authors from the Institute of Earth Physics of the Academy of Sciences of the USSR and the Research Institute of Geophysics. The paper compared DSS with other methods for studying the structure of the Earth's crust, and noted the extensive, though not yet fully exploited, possibilities of this method, which is the most detailed. The possibility of using DSS for detecting and interpreting waves reflected from deep interfaces and for utilizing different types of waves (refracted, exchanged, etc.) was emphasized.
The use of reflected waves in DSS was discussed by E. D. Tagai and N. P. Ivanova, as well as by V. Z. Ryaboi and G. G. Shteinberg.
2. Papers of the second category dealt with the results obtained by DSS in regions having different geological histories, including ancient and young shields (such as those of Karelia, the Volga-Ural regions, Turkmenia, and Kazakhstan), intermontane troughs (Fergana, Western Turkmenia, the Kura lowland), folded regions (Tien Shan and Pamir) inland seas (Black and Caspian), and the transition zone from the Asian continent to the Pacific Ocean (the northern coast, the Sea of Okhotsk, the Kurile Island Arc and its accompanying trench, and the northwestern margin of the Pacific). Papers on these subjects were presented by I.V. Litvinenko. I.V. Pomerantseva, A. V. Egorkin, K. E. Fomenko, A. A. Popov, B. S. and I. S. Vol'vovskii, B. D. Trebukova, T. L. Vasil'eva, Yu. M. Neprochnov, P. S. Veitsman, E.I. Gal'perin, N. I. Davydova, I. P. Kosminskaya, R. M. Krakshina, and others.
The majority of the authors devoted most of their attention to the characteristics of wave patterns and the determination of the physical nature of the recorded waves.
B. S. and I. S. Vol'vovskii, I. V. Pomerantseva, I. V. Margot'eva, and A. V. Egorkin reported that alongside the head waves the records often show deep waves similar to refracted ones, as well as waves reflected from Moho beyond the limiting angle.
A. S. Alekseev presented some theoretical results, while A. M. Epinat'eva and A. G. Aver'yanov presented analyses of experimental data and calcula tions for certain specific models of a medium approximating different Earth crust models in its basic features.
I. P. Kosminskaya reported on work done by several authors in the transition zone from the Asian continent to the Pacific, as well as on an analysis of the various wave patterns obtained in different areas of the investigated region. Observations on seas and oceans permit a much
more comprehensive use of the dynamic and kinematic properties of the recorded waves. The advantage derives mainly from the constant conditions for the generation and recording of vibrations as well as from similarities in the directional characteristics of the source and the detector. Analysis of the kinematic and dynamic features of the recorded wave patterns revealed, and made possible the utilization of the head waves related to deep interfaces as well as of refracted and reflected waves and those of more complex types, such as multiple and exchange waves.
Preliminary results obtained by using the entire variety of wave patterns make it possible to determine the most probable velocity sections of the Earth's crust which are characteristic of the different areas investigated, thereby isolating several corresponding types of crustal structure, the most distinct being the continental type (characteristic of shields), the oceanic, and the transitional.
Yu. N. Godin presented his concept of the multilayer structure of the Earth's crust, involving the absence of the so-called classical layers (the granite and the basalt layers), and assuming the presence in the crust of only metamorphic sedimentary complexes of various geological ages. His viewpoint was supported by I.A. Rezanov. Godin also suggested that in the near future work should be restricted to methodical experiments aiming at refining DSS. He stated that in its present form this method cannot solve practical problems concerning the distribution patterns of mineral resources, and therefore the time has not yet come for its large scale implementation for regional investigations.
A different viewpoint was developed by V.V. Fedynskii, B.A. Petrushev skii, I. P. Kosminskaya,and others who claimed that along with the search for further improvements, more extensive use be made of DSS, which has been adopted in practice as part of the efficient complex of regional geo physical investigation methods.
Petrushevskii insisted on extensive use of DSS even for determining the more general structural features of the Earth's crust for purposes of regional geotectonic zoning, which directly provides an efficient basis for the prospecting of minerals. According to this author DSS provides the most powerful tool for investigating the deep layers of the Earth's crust that has yet been invented; the failure to implement this method cannot be justified.