Advances in seismology and extensions of its application have made it increasingly necessary to perform high-sensitivity observationsonartificial earth tremors (explosions) or on natural ones. This implies in particular to investigating the seismic conditions in large industrial centres. There are many major cities with a million inhabitants or more in seismically-active regions. In the USSR, this applies to the capitals of the Union Republics such as Alma Ata, Frunze, Tashkent, Dushanbe, and Ashkhabad, as well as to dozens of local entres and cities with extensive industrial development. Seismic classification and earthquake forecasting have to be considered in relation to the extension or building of cities in such regions, and this would be impossible without detailed investigation of the seismicity, which involves upgrading the instru mental observation network. The demand for detailed information on the seismicity increases with every extension to the construction. A successful solution here can be implemented only by taking account of some specific factors, the main one being the high level of seismic noise due to the activities in large centres, which restricts the sensitivity of the apparatus and makes it impossible to record weak local earth tremors, which are of particular interest in periods of relative seismic calm. Stations at sufficiently great distances from the city do not sense the city noise, but they also fail to record weak local earth tremors. Also, the accuracy ofobservation falls for those tremors that can be recorded because of the great distances between stations."

The present book is the author's third on the subject of vertical seismic profiling (VSP). Ten years have elapsed since the pUblication of the fIrst book. During this period, VSP has become the principal method of seismic observations in boreholes and the chief method of experimental studies of seismic waves in the real earth. VSP combines borehole studies in the seismic frequency band, well velocity surveys, proximity or aplanatic surveys, all of which previously existed as separate methods. The high effectiveness ofVSP, its great practical value, the express nature and clarity of the results obtained have all contributed towards a very rapid acceptance of the method. In the USSR VSP has been used in an overwhelming majority of areas and is being used increasingly in many foreign countries as well. This has been greatly facilitated by the translation into English and the publication in the U. S. A. by the Society of Exploration Geophysicists of the book Vertical Seismic Profiling (Tulsa, Oklahoma, 1974). As the method has become more familiar, it has attracted growing interest outside the USSR This has been substantiated by the special seminar on VSP (Oklahoma, 1979) which was organized for 22 U. S. companies and universities and presented by the author.

The present book is the author's third on the subject of vertical seismic profiling (VSP). Ten years have elapsed since the pUblication of the fIrst book. During this period, VSP has become the principal method of seismic observations in boreholes and the chief method of experimental studies of seismic waves in the real earth. VSP combines borehole studies in the seismic frequency band, well velocity surveys, proximity or aplanatic surveys, all of which previously existed as separate methods. The high effectiveness ofVSP, its great practical value, the express nature and clarity of the results obtained have all contributed towards a very rapid acceptance of the method. In the USSR VSP has been used in an overwhelming majority of areas and is being used increasingly in many foreign countries as well. This has been greatly facilitated by the translation into English and the publication in the U. S. A. by the Society of Exploration Geophysicists of the book Vertical Seismic Profiling (Tulsa, Oklahoma, 1974). As the method has become more familiar, it has attracted growing interest outside the USSR This has been substantiated by the special seminar on VSP (Oklahoma, 1979) which was organized for 22 U. S. companies and universities and presented by the author.

variegated seismological conditions has been accumulated. The method has been developed further in two main directions: - the perfection of the techniques and equipment of three-component field studies incorporating a continuous control of the identity of equipment both in deep boreholes and on the surface; - the creation of efficient and straightforward software for the automatic processing of PM data. Whereas the early stages of development of the method have been conspicuous chiefly by the use of polarization for the discrimination of the wave field, in recent years the emphasis shifts to the use of polarization parameters to obtain additional information about the Earth. This is especially important, as the polarization parameters are very sensitive to inhomogeneities in cross-section and enable those parameters of the Earth to be studies which cannot be obtained from kinematics. Here one should especially mention the polarization of transverse waves, which can act as one of the most reliable parameters for identifying and studying anisotropic properties of the Earth. At present various modifications of PM are being developed applicable both to uphole - (PM RW = reflected waves method, PM CDP = common-depth-point method, PM refracted-wave method, PM of regional studies utilizing earthquakes) and to downhole observations (PM VSP = vertical seismic profiling). Not all the PM modifications are developing at the same rate. The method which has up to now been developed most extenSively is PM VSP.

Advances in seismology and extensions of its application have made it increasingly necessary to perform high-sensitivity observationsonartificial earth tremors (explosions) or on natural ones. This implies in particular to investigating the seismic conditions in large industrial centres. There are many major cities with a million inhabitants or more in seismically-active regions. In the USSR, this applies to the capitals of the Union Republics such as Alma Ata, Frunze, Tashkent, Dushanbe, and Ashkhabad, as well as to dozens of local entres and cities with extensive industrial development. Seismic classification and earthquake forecasting have to be considered in relation to the extension or building of cities in such regions, and this would be impossible without detailed investigation of the seismicity, which involves upgrading the instru mental observation network. The demand for detailed information on the seismicity increases with every extension to the construction. A successful solution here can be implemented only by taking account of some specific factors, the main one being the high level of seismic noise due to the activities in large centres, which restricts the sensitivity of the apparatus and makes it impossible to record weak local earth tremors, which are of particular interest in periods of relative seismic calm. Stations at sufficiently great distances from the city do not sense the city noise, but they also fail to record weak local earth tremors. Also, the accuracy ofobservation falls for those tremors that can be recorded because of the great distances between stations."